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Subcommittee on Hydrology (SOH) Extreme Storm Events Work Group (ESEWG)

Workshop Synthesis Report

Workshop to Define Needed Extreme Precipitation Products

May 15, 2014, National Weather Service Offices, Silver Spring, MD

Introduction

The Extreme Storm Events Work Group (ESEWG) held a workshop to define needed extreme storm products on May 15, 2014 at the NOAA, National Weather Service Headquarters, Silver Spring, Maryland. The workshop was in response to a request from the Advisory Committee on Water Information (ACWI) to prepare a detailed proposal identifying needed extreme storm products for the nation. The requested proposal aims to incorporate the needs of the Federal and State agencies for assessing extreme storm events, and the resources needed to satisfy those identified agencies’ needs. The workshop was developed by the ESEWG over a six month period, and in consultation with the Subcommittee on Hydrology (SOH) leadership.

As directed by the ACWI secretariat, the workshop was open to the public. Victor Hom, SOH Chair and NOAA/NWS representative to SOH was the workshop host. Victoria Sankovich-Bahls, U.S. Bureau of Reclamation was the workshop facilitator. Robert Mason, SOH Vice-Chair and U.S. Geological Survey representative to SOH was also present. Mark Perry, Dam Safety Engineer, State of Colorado led the discussion of the State dam safety officials on their current application of extreme precipitation data and information from their States’ perspective. The workshop agenda and participant list are included as attachments.

The workshop objective was to clearly define extreme storm products that are needed for deterministic and risk-informed infrastructure decision making by State and Federal agencies, now and in the future. In meetings prior to the workshop, the ESEWG had discussed a range of product needs: primarily, updating the Hydrometeorological Report (HMR) series which provide estimates of Probable Maximum Precipitation (PMP); completing NOAA Atlas 14 which provides precipitation frequency estimates; further developing and completing a national storm catalogue which provides detailed maps of precipitation distribution over a watershed, and meteorological analysis for historic storms that produced rainfall likely to influence estimates of PMP.

Questionnaires

To facilitate the workshop objective, the ESEWG prepared and sent to the SOH leadership, two questionnaires, one for the Federal Agencies (attachment #3); and one for the State agencies

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involved in dam safety assessments (attachment #4). Victor Hom and Robert Mason sent the questionnaires to all of the Federal agencies on the SOH, and to the State agencies identified by the Interagency Committee on Dam Safety (ICODS) and National Dam Safety Review Board (NDSRB). Victor Hom and Tom Nicholson, Chair, ESEWG had earlier met with and presented to the ICODS and NDSRB members on April 24, 2014 at their quarterly meeting, to inform them of the planned ESEWG workshop and questionnaires to be circulated prior to the workshop. These questionnaires were developed earlier by the ESEWG members through many teleconferences, along with a review of the Federal and State surveys in Appendix D of FEMA’s “Summary of Existing Guidelines for Hydrologic Safety of Dams,” in FEMA report P-919 issued in July 2012.

The Federal questionnaire (see attachment #3) provided a preamble to inform the Federal agencies as to the reason for the questionnaire, and the utility of its responses in developing the proposal requested by ACWI. The preamble states:

“Extreme storm hydrometeorology studies impact extreme flood estimates and assessments for dams, nuclear power plants, levees, and other high-hazard structures within the United States. Additionally, environmental impacts from extreme storm events are of increasing concern. The Extreme Storm Events Work Group is responsible for reviewing and improving methodologies and data collection techniques used to develop design precipitation estimates of large storm events up to and including the Probable Maximum Precipitation. The charter for the Work Group states that it will develop a detailed scope of work/plan of study and determine the necessary funding requirements to update the Catalog of Extreme Storms and Hydrometeorological Reports (HMRs). The Work Group is also tasked with developing a list of individual Federal Agency extreme storm product needs. From ongoing discussions and recent advances to probabilistic methodologies for risk-assessment, it is evident that updates to the Catalog of Extreme Storms and Hydrometeorological Reports may not fully address the national needs. This questionnaire asks each Agency to critically evaluate their views, methods, data sources, tools, etc. regarding extreme storm events and to identify any needs and/or gaps in extreme storm event information. In a Writing Workshop scheduled for later this year, the answers to the questionnaires will be synthesized to define extreme storm product(s) that are needed for deterministic and risk-informed infrastructure design. The product(s) and corresponding schedule(s) and cost(s) will be presented in a proposal to ACWI-SOH.”

For example, the Federal questionnaire requested the responder to:

“Discuss your agency methods and extreme precipitation needs for decision making, assessments, and designs (extreme precipitation is defined as those events with a return period of 1,000-years or greater, up to and including PMP):

a. What extreme precipitation data do you use in your decisions?

b. How is this extreme precipitation data used?

c. What is the scale and resolution of this data (regional, site-specific, watershed-specific)?

d. What is the spatial extent to which this data is applied?

e. Would it be beneficial if this data were updated? And why is that?

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f. What decisions are made by utilizing this data? Discuss your agency methods and extreme precipitation needs for decision making, assessments, and designs (extreme precipitation is defined as those events with a return period of 1,000-years or greater, up to and including PMP).”

These and other questions set the focus and content of the Federal agencies’ responses which was reflected in their presentations at the workshop.

Similarly, the State questionnaire (attachment #4) provided a preamble and list of questions to the State dam safety officials to learn of their needs for extreme storm information and analysis. This information was discussed in the afternoon’s panel discussion by the State dam safety officials lead by Mark Perry.

Workshop Presentations

Victor Hom’s opening remarks identified the mission of the SOH and the history of the ESEWG. He described the ESEWG charter (http://acwi.gov/hydrology/extreme-storm/ESEWG_Charge_SOW_final_24July2008.pdf) and the reason for the workshop.

He mentioned that the overall purpose of the Extreme Storm Events Work Group is to coordinate studies and databases for reviewing and improving methodologies and data collection techniques used to develop design precipitation estimates of large storm events up to and including the Probable Maximum Precipitation (PMP).

As stated in the ESEWG Charter, ACWI has charged the Work Group to develop a detailed scope of work/plan of study, and determine the necessary funding requirements to update the Catalog of Extreme Storms and Hydrometeorological Reports (HMR) for estimating PMP.

Victor also referenced the recommendations that came out of the Workshop on Probabilistic Flood Hazard Assessment (proceedings posted at: http://www.nrc.gov/reading-rm/doc-collections/nuregs/conference/cp0302/) which was supported by many of the SOH agencies. These recommendations were:

Explore the use of “Expert Assessments (Elicitation)” to formulate flooding scenarios, estimate modeling parameters;

Work cooperatively with other Federal Agencies to develop PFHA strategies for coastal storm surges and riverine flooding at the site-specific and watershed scales;

Investigate available hydrometeorological databases and analysis methods related to NOAA Atlas 14 and the USACE Storm Catalogue for use in PFHA; and

Review U.S. and international technical approaches to identify strategies to fill information gaps in PFHA (e.g., paleofloods, paleo-oceanography, dam and levee failure analyses).

Victoria Sankovich-Bahls provided an overview of the workshop objective, goal, program and expected products to be discussed. She identified the general areas of mutual interest as:

• Extreme Storms Catalog

• Probabilistic Flood Hazard Approaches

• Probable Maximum Precipitation

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• Site-Specific Guidelines for Estimating PMP

The workshop activity is to refine these general areas into the following tasks:

• Determine the product needs and requirements for a National Catalog of Extreme Storms;

• Determine a path forward for updating Hydrometeorological Reports (HMR); • Develop recommendations and gather requirements for site-specific PMPs; and • Develop national recommended guidelines for Probabilistic Flood Hazard Assessment in

design, analysis, or safety evaluations.

Each Federal agency presenter presented their responses to the Federal questionnaire with a focus on current application of extreme precipitation data and information.

1. Natural Resources Conservation Service (NRCS)

The first presenter was Claudia Hoeft, National Hydraulic Engineer, NRCS. She provided a short history of NRCS’s predecessor, the Soil Conservation Service (SCS). The SCS was formed in 1935 to address soil erosion due to severe drought conditions. To stabilize the soil during the “Dust Bowl” years, SCS encouraged development of conservation plans. These plans would assist in addressing many natural resources problems including soil erosion; flooding; animal waste management; wetland and wildlife habitat preservation, and restoration and management. In the 1940s and 50s, the SCS, now the NRCS, assisted in the design and construction of over 11,000 dams to reduce flooding and minimize erosion. The peak of dam construction was in 1963. 605 dams reached their 50 year life in 2013. Victor Mockus, an early hydrologist working for the Civilian Conservation Corps and SCS, was known as the father of SCS hydrology. He focused on rainfall and runoff issues.

In 1956, ARS and SCS, began to develop standardized hydrologic procedures for small, ungaged, agricultural watersheds which led to the publication of Section 4 of the National Engineering Handbook in 1964 (now the National Engineering Handbook, Part 630 - http://directives.sc.egov.usda.gov/viewDirective.aspx?hid=21422). The concepts in the National Engineering Handbook, Part 630 included: (1) a system for grouping soils according to infiltration capacity; (2) a standard system of determining runoff potential of watersheds according to soils and land use (Runoff Curve Number procedure); and (3) use of a dimensionless unit hydrograph in estimation of peak rates of runoff. Victor Mockus, who started his career with the CCC is responsible for the development, or at least the refinement of many of the NRCS hydrology procedures in use today. While the runoff curve number procedure in particular has received a lot of scrutiny and review by the scientific and academic communities, it seems to be withstanding the test of time and is still probably the most widely used procedure for making estimates of runoff volume. Today, NRCS maintains a number of documents which have become standard hydrology references world-wide.

Approximately 160 NRCS conservation practice standards provide information on and where the NRCS practices are applied. The NRCS standards set forth the minimum quality criteria including hydrologic criteria where applicable. (http://www.nrcs.usda.gov/wps/portal/nrcs/main/national/technical/cp/ncps/)

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For example, the minimum auxiliary spillway capacity for POND (Conservation Practice Standard Number 378) is provided in the table below:

Drainage area (acre)

Effective height of dam1 (ft)

Minimum design storm2

Storage (acre-ft)

Frequency (Years)

Minimum duration (hours)

20 or less 20 or less < 50 10 24

20 or less > 20 < 50 25 24

> 20

< 50 25 24

All others

50 24

NRCS Technical Release (TR) 60 “Earth Dams and Reservoirs” issued in July 2005 sets their policy on design of dams. TR60 describes design procedures and provides minimum requirements for planning and designing earth dams and associated spillways. It is essential that these dams be constructed with uniform criteria to ensure consistent performance. TR-60 specifies the PMP event to generate freeboard hydrograph (FBH) for High Hazard Dams; to analyze the integrity, or erosion resistance, of earthen materials in auxiliary spillway; and to set top of dam elevation. http://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=24937.wba

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The TR-60 Minimum Auxiliary Spillway Hydrologic Criteria is provided in the table below:

1 P100 = Precipitation for 100-year return Period. PMP = Probable maximum precipitation 2 Dams involving industrial or municipal water are to use minimum criteria equivalent to that of Significant

Hazard Class. 3 Applies when the upstream dam is located so that its failure could endanger the lower dam

Claudia stated that there is a need for updated/current PMP (and other) rainfall data to address: (1) flood hazard and other studies that rely upon hydrologic analyses; (2) project design; (3) the need to use the most current and available information; (4) climate change considerations; (5) questions from project sponsors and others about why NRCS may not be using the must currently available data; and (6) questions about using Special Studies developed outside the Federal realm.

NRCS issues and concerns are: (1) NRCS is a technical Agency providing assistance to landowners; (2) NRCS is a consumer of rainfall data, including PMP studies, and (3) Very few personnel within NRCS have knowledge or ability to develop or evaluate PMP studies.

NRCS Primary Needs are: (1) Updated PMP estimates; (2) Access to studies and accompanying background information (such as historical extreme storms databases); and (3) access to and support in using tools developed by other Federal Agencies (HEC-MetVue); and

Class of Dam

Product of storage x effective height

Existing or planned upstream dams

Precipitation data for 1

Auxiliary spillway hydrograph

Freeboard hydrograph

Low2

less than 30,000

none

P100 P100 + 0.12(PMP - P100)

greater than 30,000

P100 + 0.06(PMP - P100)

P100 + 0.26(PMP - P100)

all any3 P100 + 0.12(PMP - P100)

P100 + 0.40(PMP - P100)

Significant all none or any

P100 + 0.12(PMP - P100)

P100 + 0.40(PMP - P100)

High all none or any

P100 + 0.26(PMP - P100)

PMP

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(4) clear guidance on development of regional and site-specific studies to ensure consistency of studies developed outside of the Federal realm.

2. U.S. Geological Survey (USGS)

Robert Mason, USGS discussed the uses of extreme precipitation estimates by the USGS. The USGS operates and maintains over 8,000 streamgages across the U.S. There are 24,000 sites with historical records (annual peaks dating to 1700’s). The USGS also deploys temporary gages and sensors as part of its observational system. To provide effective situational awareness to the public, government agencies, and industry, the USGS maintains numerous online Websites: WaterWatch, WaterAlert, WaterNow, Flood Inundation Mapping (FIM), and many contributions to the missions of other agencies. The USGS also conducts studies and surveys for fundamental understanding of hydrology through research and interpretation, and methods development. The USGS also provides regional characterization and regionalization data and information through StreamStats.

Robert explained that regionalization was a systematic process of explaining flood-frequency characteristics (1-percent chance flood, 7Q10, etc.) by linking them to basin characteristics through regression. The regression analysis was a statistical analysis that defines a relationship between a dependent variable and one or more explanatory variables. An example dependent variable would be the 1-percent chance flood. The example explanatory variables include: drainage area, mean annual precipitation, and main channel slope. This analysis is used to estimate flows for ungaged sites. The potential errors are defined when applied within known bounds.

The Regression Equation is:

Q100 = 5.39DA0.874(E/1000)-1.13P1.18

where:

Q100 is the 100-year flood, in cubic feet per second

DA is Drainage Area, in square miles

E is mean basin elevation, in feet

P is mean annual precipitation, in inches

Precipitation is strong explanatory variable in only 40 regression equations (out of about 5,000). It is used only in 18 States, generally for a 24-hour duration with 2, 25, 50, 100-year Recurrence Intervals in approximately equal frequency.

3. Federal Energy Regulatory Commission (FERC)

Ken Fearon, FERC, discussed FERC’s application, need and support of ESEWG products. FERC has responsibility for regulating non-federal dams with hydroelectric power plants. FERC reviews the design, construction, operation, maintenance, use, repair, or modification of any project works which are subject to FERC jurisdiction under the supervision of the Regional Engineer or any other authorized Commission representative for the purpose of:

(i) Achieving or protecting the safety, stability, and integrity of the project works or the ability of any project work to function safely for its intended purposes, including navigation, water power development, or other beneficial public uses; or

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(ii) Otherwise protecting life, health, or property.

FERC is responsible for the safety and adequacy of 2,523 non-Federal, jurisdictional dams (i.e., 803 high-hazard potential dams, 176 significant-hazard potential dams and 1,544 low-hazard potential dams). The Commission, through its dam safety program requires jurisdictional dams to have adequate spillway capacity to pass the project’s Inflow Design Flood (IDF).

The IDF is the flood flow above which the incremental increase in flow and water surface elevation due to a failure of a dam or other water impounding structure is no longer considered to present an additional, unacceptable threat to downstream life or property.

Spillway adequacy determinations are based on the results of an IDF, Probable Maximum Flood (PMF), and site-specific PMP studies. The IDF is selected based on hydraulic computer modeling and uses an incremental hazard potential evaluation to determine the consequences of dam failure. The PMF is considered the upper limit of an IDF analysis.

The PMF is determined using the guidance in Chapter 8 of FERC’s Engineering Guidelines (see: http://www.ferc.gov/industries/hydropower/safety/guidelines/eng-guide/chap8.pdf ), and utilizes the appropriate Hydrometeoroglical Reports (HMRs) to estimate the PMP. The general and local PMP values chosen are those for the 6, 24 and 72-hour durations. In some cases, a licensee may request to perform an optional site-specific PMP study to determine the PMP. These studies may be approved when refinement of PMP values in HMR is considered beneficial, particularly for areas considered less reliable due to orographic effects (also known as the Stippled Region); or when new extreme storm data is available and was not included in the existing HMR.

FERC requirements for site-specific PMP studies are: (1) the studies must be performed by a qualified hydrometeorologist; (2) the studies must be reviewed by a Board of Independent Consultants (BOC) consisting of three or more qualified professionals that usually include a meteorologist, hydrologist, and civil engineer; (3) approval of the BOC by FERC; and (4) FERC representatives must be involved throughout the study and BOC process. Several site specific PMP studies have been performed at FERC jurisdictional projects including but not limited to the following: Deerfield-Harriman Dam, 1987; Upper and Middle Dams, 2002; Brassua Dam, 2012; and Santa Felicia, 2012. In addition, a series of state-wide studies have been completed, including Nebraska, 2011; Ohio, 2012; and Arizona, 2013 with additional state studies underway (Wyoming and Virginia),

FERC’s site-specific studies methodologies follow procedures outlined in the HMR’s with updated procedures including: (1) updated rainfall analysis of recent extreme events; (2) use of Hybrid Single Particle Lagrangian Integrated Trajectory (HYSPLIT) model; (3) use of average dew points; (4) use of Sea Surface Temperatures; (5) use of the Storm Precipitation Analysis System (SPAS); (5) use of Next Generation Weather Radar (NEXRAD); (6) consideration of orographic influences; and (7) use of GIS tools.

Additional extreme storm resources used by FERC include: (1) NOAA Atlas 2 is used for 100-yr frequency estimates for those areas not covered by NOAA Atlas 14; (2) NOAA Atlas 14 is used for 100-yr and 1,000-yr frequency estimates; and (3) State-wide site-specific studies provide updated storm information and methodology.

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FERC identified the benefits of updated HMR’s as: (1) inclusion of additional storm records; (2) Inclusion of advancements in science and technology; (3) nationally consistent application of PMP methodology; (4) uniform application by HMR users; and (5) reduced agency and dam owner costs.

Improvements sought by FERC are: (1) an updated storm catalog presently being developed by USACE; (2) reduced subjectivity in procedures; (3) transparent and consistent procedures; (4) an ability to assess large basin areas; (5) provide seasonal guidance; (6) consideration of snowmelt; (7) assess orographic effects; (8) provide full documentation; (9) estimate frequency of PMP values for use in risk analyses; and (10) development of more consistent methodologies. Although FERC has no budget provisions for funding research, FERC could provide r technical and peer review assistance.

Thus the Federal Energy Regulatory Commission has an interest in any coordinated effort to review extreme storm data and update HMR’s for use in extreme storm development. Currently the engineering profession is developing PMF values for extreme storm events based on outdated storm information. The Commission supports the efforts of the Extreme Storm Events Work Group to promote the cooperation and coordination among agencies to improve methodologies and data collection techniques to develop estimates of large storm events up to and including the Probable Maximum Precipitation (PMP).

4. U.S. Nuclear Regulatory Commission (NRC)

Joseph Kanney, NRC discussed NRC’s goal of developing and implementing risk-informed and performance-based regulation. Dr. Kanney used the following diagram to illustrate the relationship between the traditional deterministic approach and the increased value of risk-informed, performance-based regulations.

What can go wrong?

How likely is it?

What are the consequences?

What performance is needed?

Risk Information

Traditional Deterministic Approach

Risk-informed

Performance-based

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NRC regulations require that structures, systems, and components (SSCs) of nuclear facilities important to safety be designed to withstand the effects of natural phenomena (e.g., earthquakes, tornadoes, hurricanes, floods, tsunami, and seiches) without loss of capability to perform their safety functions. The design bases for these SSCs must reflect: (1) appropriate consideration of the most severe of the natural phenomena that have been historically reported for the site and surrounding area, with sufficient margin for the limited accuracy, quantity, and period of time in which the historical data have been accumulated; (2) appropriate combinations of the effects of normal and accident conditions with the effects of the natural phenomena; and (3) the importance of the safety functions to be performed.

The types of facilities/sites for which extreme precipitation estimates are needed to support flood hazard assessments covers a wide range (e.g., nuclear power plant sites and designs, fuel cycle facilities, interim spent fuel storage facilities, nuclear waste repositories, watersheds in which nuclear facilities are located, reservoirs and dams upstream of nuclear facilities, and tailings dams).

Analysis of flooding hazards submitted for licensing of new facilities is currently almost entirely deterministic, commonly applying a progressive refinement of conservative assumptions referred to as the Hierarchical Hazard Assessment (HHA) approach. Concepts such as Probable Maximum Precipitation (PMP) and Probable Maximum Flood (PMF) are typically used. NRC regulatory guidance and standard review plans specifically call for use of PMP estimates developed using NWS Hydrometeorological Reports (HMRs).

For new reactor licensing using the HHA approach, PMPs from the HMRs used to construct extreme flood scenarios for two common scenarios: (1) application of the PMF for riverine flooding; and (2) local intense precipitation (LIP) for evaluation of site drainage. PMP values from the HMRs are also used to determine design basis loads on structures due to rain, ice and snow events. The 48-hour cool season PMP is typically used for estimating snow/ice loads. HMR 51 and 52 are used most often HMR 49, 53, 55A, 57 and 59 have also been used. Recently NRC licensees have submitted “site-specific” PMP analyses performed under contract by private consultants, which pose a challenge for NRC staff reviewers.

Oversight of operating nuclear facilities uses more a explicitly risk-informed approach known as the significance determination process (SDP). SDP is used for decision-making in light of new information that comes up after initial licensing. SDP activities have often included attempts to quantify risks due to natural hazards such as extreme precipitation and flooding. NOAA Atlas 14 and its precursor, Weather Service Technical Report 40, have been used to review frequency estimates of extreme precipitation at the facility site. With respect to flooding hazards, the SDP focus is on estimating the frequency of an initiating event. The initiating event frequency is combined with system fragility information to obtain risk insights (often qualitative, and not rigorous).

In summary, the decisions being made that rely on extreme precipitation estimates involve licensing of proposed projects and oversight of operating facilities. Licensing decisions for proposed projects focus on the suitability of specific sites and the design basis of facilities at those sites (e.g., design basis flood estimates, and design loads on structures due to both liquid and solid precipitation). For the oversight of operating facilities under the SDP process, decisions involve assigning a significance/severity to identified deficiencies. Depending on the identified severity, orders to modify facilities can be issued and fines can be assessed.

Following the earthquake and severe tsunamis flooding of the Fukushima Daiichi nuclear plants in Japan in March 2011, NRC issued a “Request for Information” instructing all licensees of

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operating commercial nuclear power plants to develop and report updated earthquake and flood risk information for comparison against original licensing information. For sites where flood elevations and associated effects exceed the original licensing basis, licensees are expected to perform an integrated assessment to evaluate their flood protection features and procedures, as well as any flood mitigation strategies. The flood hazard reevaluations and integrated assessments will form the basis for regulatory decisions. The potential decisions range from changes in regulations regarding hazard assessment, protection and mitigation to modification of individual licenses.

For the requested Post-Fukushima flood re-evaluations, licensees and their contractors use PMP values from the HMRs in some cases and in others, rely on site-specific PMPs. During this review period, some licensees are actively revising protection and mitigation measures that depend in part on the HMR’s PMP estimates. Licensees are interested in using probabilistic methods to support integrated assessments.

Dr. Kanney stated that an “update” to the HMRs, and particularly HMR51, which applies to the majority of NRC-licensed facility locations would be beneficial for NRC’s current deterministic methods. These updates should include a review of potential storm model improvements that could be used to improve estimates. Simply plugging new data into an old method without considering adjustments to that method based on decades of experience since the last update of the HMR 51-52, for example, doesn’t seem appropriate. The updating should address limitations on basin size and the questionable applicability in the “stippled” regions affected by orographic effects. Other recommendations include; (1) more focus on the probabilities associated with PMP estimates (critical component to risk informed decision making); (2) give attention to cool season precipitation (useful for determining design basis snow and ice loads on structures); (3) provide guidance with regard to site-specific PMP values (an increasing regulatory challenge); and (4) provide online digital product similar to the NOAA Atlas 14 Precipitation Frequency Data Server.

With respect to NOAA Atlas 14, NRC currently makes limited use of the precipitation frequency estimates it provides in safety oversight of operating commercial nuclear facilities. Concerning extrapolation of NOAA Atlas 14 estimates beyond the currently available average return intervals of 1,000 years, they are performed on a limited basis and as a risk-informed exercise to evaluate information submitted to the NRC, since multiple licensees have performed such extrapolations on NOAA Atlas 14 and other hydrologic databases, as a way to respond to NRC regulatory activities. NRC staff is not necessarily interested in pursuing these limited credibility extrapolations, but rather responding to requests to consider risk insights based on submitted information. NRC staff is aware of the limited technical justification for doing so and therefore uses significant caution in these cases. In order for NOAA Atlas 14 to be of broader use to NRC staff, it would need to address more useful return periods usually in excess of 1,000 years (i.e., up to and beyond 1,000,000 years) of interest to the NRC.

Research efforts are being implemented to develop probabilistic flood hazard assessment (PFHA) technical basis to support risk-informed design basis flood estimation guidance.

5. Tennessee Valley Authority (TVA)

Mike Eiffe, TVA portrayed the Tennessee River system and watershed to include its numerous dams and reservoirs. He identified the HMRs and special study reports used by TVA. The list included: (1) HMR-41 issued June 1965; 6- to 72-hour TVA and PMP estimates for two watersheds above Chattanooga; (2) HMR-47 issued May 1973; 6- to 72-hour TVA and PMP estimates for two watersheds below major tributary dams; (3) Special study issued in 1979 and

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revised in 1983; 6- to 72-hour PMP estimates for Cherokee Dam watershed (3428 mi2); (4) Special study issued in 1984; 6- to 72-hour PMP estimates for Douglas Dam watershed (4541 mi2); (5) HMR-56 issued in October 1986; 1- to 72-hour TVA and PMP estimates for TN River basins < 3,000 mi2; which replaced HMR-45 issued in May 1969.

Tennessee River watershed showing tributaries, dams and reservoirs locations.

The primary usage of HMRs at TVA is to provide the design rainfall basis for PMF evaluations at TVA’s high hazard dams and nuclear power plants. The HMRs and special study reports provide the design rainfall basis for MPF evaluations at TVA’s significant and low hazard dams. Mike Eiffe noted that the PMF and MPF probabilities are not known.

An important challenge for TVA is the reduced staffing levels of hydrologists over the years. In September 1979, the Flood Control Branch had 15 staff in hydrology, 20 staff in hydraulics and 15 staff in floodplain management. Today, there is only 4 staff in river management to cover the same topics as in 1979. These staffing changes were due to reductions in the operations and management budget.

The current ESEWG-related work at TVA includes: (1) updating PMP and TVA Precipitation Estimates by TVA’s contractor, Applied Weather Associates which is on schedule and within budget. This effort is scheduled for completion in calendar year 2014, and provides input for the assessment of 27 dams involving five nuclear power plant locations. Work is also underway for the development of basin-average precipitation frequency relationships by TVA’s contractor, Riverside Technology Inc. Phase 1 of this work is on schedule and within budget, whereas, Phases 2 and 3 have not yet been funded. This work is likely to be completed in fiscal year 2015 depending upon funding levels. The work targets 10 watersheds in the Tennessee River system.

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Recent studies involve basin-averaged rainfall estimates using observed precipitation from the Lower Mississippi River Forecast Center’s (LMRFC) multi-sensor precipitation estimates (MPE), National Severe Storm Laboratory’s (NSSL) next generation (Q2) quantitative precipitation estimation (QPE) product; and climatology-weighted gage interpolation. This study will provide forecasted precipitation using the LMRFC quantitative precipitation forecasts (QPF), and the high-performance computing (HPC) products at the 5% and 95% levels.

TVA is developing and utilizing new runoff models in conjunction with the LMRFC. These models include the Sacramento – Soil Moisture Accounting (SAC-SMA) runoff model, and the Lag and K (Lag/K) routing model. The earlier-mentioned precipitation studies will provide input to these models for assessing floods. For hydraulics modeling, TVA is applying the HEC-RAS model (version for major rivers involving dam break analysis) to the 1900 miles of river courses of the Tennessee River Basin which includes 28 dams. TVA plans to calibrate the model across a range of flows, and will incorporate the calibrated model into their river management operations.

TVA’s short term goals include: (1) complete the PMP update study; (2) revise PMF estimation as required; (3) complete the precipitation frequency study; (4) complete the SAC-SMA model calibration; (5) complete the HEC-RAS model calibration; and (6) begin development of the Risk-Informed Decision Making (RIDM) simulation models.

6. NOAA/National Weather Service (NWS)

Geoffrey Bonnin, NWS, discussed lessons learned from the development, publication and application of NOAA Atlas 14 (http://www.nws.noaa.gov/oh/hdsc/index.html). NOAA Atlas 14 begun in 2000 was developed by the NWS on behalf of the Federal Government to provide precipitation frequency (PF) estimates for various durations (less than 1 hour; between 1 and 24 hours; and beyond 24 hours through 60 days) for various areas of the U.S. These estimates are published as volumes in the NOAA Atlas 14 series by States/Territory. The status of the published volumes (at the time of the workshop) (see: http://www.nws.noaa.gov/oh/hdsc/currentpf.htm) is provided in the map below:

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Along with NOAA Atlas 14, the NWS has developed and maintained a “Precipitation Frequency Data Server” (PFDS) (see http://hdsc.nws.noaa.gov/hdsc/pfds/index.html) which is web-based interface developed to deliver NOAA Atlas 14 precipitation frequency estimates and associated information. Upon clicking a State on the map above or selecting a state name from the drop-down menu, an interactive map of that state will be displayed. From there, a user can identify a location for which precipitation frequency estimates are needed.

Estimates and their confidence intervals can be displayed directly as tables or graphs via separate tabs. Links to supplementary information (such as ASCII grids of estimates, associated probabilistic temporal distributions of heavy rainfall, time series data at observation sites, cartographic maps, extensive documentation, etc.) can also be found.

NOAA Atlas 14 is a single source which supersedes various publications developed since late 1940s including earlier Technical Papers, Technical Memoranda and special papers which contained the superseded information.

The first lesson learned was that funding is the controlling factor. NWS had to line-up reimbursable funding from various sources such as Federal, State and local government agencies to develop the piecemeal projects (e.g., Volumes 1, 2, 3, etc.). This piecemeal funding caused great difficulties. The same science was developed, and applied area by area with no guarantee of achieving full coverage for the U.S. NWS applied state-of-the art methodologies in preparing NOAA Atlas 14 and provided information (such as confidence limits) that was not provided in previous publications. The primary changes in methodology involved new statistical techniques, improved methods for spatial interpolation between observing locations, new approaches to data quality control, and a much larger set of historical observations, both spatially and temporally and from a variety of new data sources. The funding approach necessitated Volumes based on State boundaries rather than watersheds or geographic climate

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regimes. The analysis for each Volume was extended beyond each Volume’s geographic domain, so that overlapping analyses between adjoining Volumes could be used to provide continuity at Volume boundaries.

The second lesson learned was that assembling funds from many sources was tricky in that it was difficult to identify a specific, separable work package for each funding source. To work through this challenge, funding agencies often collaborated through existing formal mechanisms so that a single Memorandum of Understanding and project plan could be developed and executed. For example, the Ohio River Basin Commission provided a vehicle for collaboration on Volume 2 for the Ohio River Basin and surrounding States. The Federal Highway Administration’s Pooled Fund Program was used for combining resources for Volumes 8 through 10.

The third lesson learned focused on project management. There needed to be a critical mass of management expertise dedicated to that role in the long term to ensure completion in accordance with the vision. In addition, the production of the precipitation frequency estimates involved combining skills from a variety of disciplines. As a result, project management needed a proper (multi-disciplinary) grasp of all aspects of the project. Project management also needed the usual attributes of properly understanding the users, the products they rely on and the different communities being served.

The fourth lesson learned focused on technical capabilities. Similar to project management, there needed to be a critical mass of technical expertise, namely: hydrology, meteorology, statistics, software development, configuration management, and quality control. The people providing the expertise needed to be dedicated to their roles for the duration of each project in order to meet project schedules and quality. Again, these experts had to have a proper grasp of the product(s), the users and the communities being served.

Mr. Bonnin also discussed the historical development and status of NWS’s Hydrometeorological Reports (HMRs) (http://www.nws.noaa.gov/oh/hdsc/studies/pmp.html).

The following table provides a listing of the HMRs with a document link, title, date and electronic document size.

Document link Title Date Size (MB)

Hydrometeorological Report No. 39

Probable Maximum Precipitation in the Hawaiian Islands

1963 3.4

Hydrometeorological Report No. 41

Probable Maximum and TVA Precipitation over the Tennessee River Basin above Chattanooga

1965 5.7

Hydrometeorological Report No. 46

Probable Maximum Precipitation, Mekong River Basin

1970 16.2

Hydrometeorological Probable Maximum Precipitation and Snowmelt Criteria For Red River of the North Above

1973 1.6

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Report No. 48 Pembina, and Souris River Above Minot, North Dakota

Hydrometeorological Report No. 49

Probable Maximum Precipitation Estimates, Colorado River and Great Basin Drainages

1977 6.2

Hydrometeorological Report No. 51

Probable Maximum Precipitation Estimates, United States East of the 105th Meridian Digitized maps

1978 3.5

Hydrometeorological Report No. 52

Application of Probable Maximum Precipitation Estimates - United States East of the 105th Meridian

1982 7.8

Hydrometeorological Report No. 53

Seasonal Variation of 10-Square-Mile Probable Maximum Precipitation Estimates, United States East of the 105th Meridian

1980 3.3

Hydrometeorological Report No. 54

Probable Maximum Precipitation and Snowmelt Criteria for Southeast Alaska

1983 4.6

Hydrometeorological Report No. 55A

Probable Maximum Precipitation Estimates - United States Between the Continental Divide and the 103rd Meridian

1988 103.5

Hydrometeorological Report No. 56

Probable Maximum and TVA Precipitation Estimates With Areal Distribution for Tennessee River Drainages Less Than 3,000 Mi2 in Area

1986 8.5

Hydrometeorological Report No. 57

Probable Maximum Precipitation - Pacific Northwest States. Columbia River (including portions of Canada), Snake River and Pacific Coastal Drainages

1994 28.3

Hydrometeorological Report No. 58

Probable Maximum Precipitation for California - Calculation Procedures

1998 10.9

Hydrometeorological Report No. 59

Probable Maximum Precipitation for California HMR58 and HMR59 shapefiles (2.9 MB)

1999 21.4

NOAA Technical Memorandum NWS HYDRO 39

Probable Maximum Precipitation for the Upper Deerfield River Drainage Massachusetts/Vermont

1984 1.9

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NOAA Technical Memorandum NWS HYDRO 41

Probable Maximum Precipitation Estimates for the Drainage Above Dewey Dam, Johns Creek , Kentucky

1985 1.4

Technical Paper No. 42 Generalized Estimates of Probable Maximum Precipitation and Rainfall-Frequency Data for Puerto Rico and Virgin Islands

1961 4.2

Technical Paper No. 47 Probable Maximum Precipitation and Rainfall-Frequency Data for Alaska

1963 3.1

Regions covered by different NWS HMR documents (as of 2012).

The HMRs do need updating since many of the existing studies are old and some predate current understandings of the causal meteorological processes. The data used in the HMRs are several decades old or older, and need updating to consider recent storm data, and advances in hydrologic, meteorologic, and geospatial analytical techniques.

Geoff suggested new ideas to consider when updating the PMP estimation guidance: should a new form of guidance be developed to include automated estimation tools; should a new web-based publication/delivery mechanism similar to the PFDS for NOAA Atlas be developed? If this work proceeds, should it provide Annual Exceedance Probabilities (AEP) between those provided in NOAA Atlas 14 and the PMP.

Geoff suggested any new effort should focus on: (1) socialization of the project and the need for appropriate resources among funders and users; (2) major project elements; (3) governance of

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the activities; (4) funding sources and agreements; and (5) project plans. The socialization and resourcing success path should be to first obtain SOH and ACWI approvals which includes buy-in from the various resource sources. Next, the project must also obtain buy-in directly from each agency through agency approval and resourcing mechanisms. These new efforts also need support from non-Federal stake-holders.

He foresees the first major project element as: (1) update the science starting with literature reviews to help define a well-targeted and time limited research program; then fund grants and in-house research for a period of approximately 2-4 years; consolidate the research findings; and then, synthesize the new approach(es). (2) re-analyze historical storms, probably with new science, and adding relevant rain events not already included. Finally, (3) modernize the Severe Storms Catalog with an understanding of the community’s needs for availability, usability and product integrity.

The second major project element is to: (1) define the new products; (2) apply the new methodology with the focus on producing new products while transitioning from research to production; (3) define new publication/delivery mechanism(s) and build and test mechanisms; (4) publish new products; and (5) provide training on the new methodology and products.

With regard to governance and funding issues, first determine who the community is, then develop collaborative governance and funding mechanisms. The project(s) must obtain community acceptance. It is important to build-in opportunities for formal public review and comment. Project plans and accountability should be established and documented. Funding is fundamental to the process. Do not proceed without the prospect of funding success since second chances are rare. The governance needs to realize the need for a long-term commitment, and an understanding how costs will be shared.

The final challenge will be to determine who does the work activities, and what will be the relationship between the separate agency efforts, both current and planned? The project management needs to be integrated and coordinated within established accountability checks. To succeed, it needs strong management to avoid diffusion of responsibility, and community acceptance that requires integrity of the process and results. Geoff thinks it is better to have single project manager through the long-term.

7. U.S. Army Corps of Engineers (USACE)

Doug Clemetson, Chief, Hydrology Section, USACE/Omaha District and Aaron Byrd, USACE/ERDC, Vicksburg, MS discussed the work of the USACE’s Extreme Storm Team. Doug Clemetson is its Team Leader. The extreme storm data needs for the USACE can be grouped into three principal areas: the dam safety program; the levee safety program; and the developing program for the extreme storm database.

For the dam safety program, the needs center on site-specific PMP studies; Hydrometeorological Reports (HMR’s) updates; and the HMR tools. For the levee safety program, the needs are for updating the Standard Project Storm Criteria, and precipitation frequency data derived from NOAA Atlas14 and its predecessors, Technical Paper (TP) 40, and

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NOAA Atlas 2. Finally, for the extreme storm database program, the needs related to extreme storm data archiving/retrieval; analysis of recent extreme storm events; and linking of the database to the USACE Hydrologic Engineering Center (HEC) models such as HEC-HMS, HEC-MetVue, and other models. Other USACE data needs relate to computation of areal reduction factors (ARF); calibration of various hydrologic models; the Stochastic Extreme Flood Modeling (SEFM); and atmospheric modeling of extreme precipitation.

The current extreme storm applications involve: (1) for the Extreme Storm Database development, use of process radar imagery and digitize the historic isohyetal maps from the HMRs; (2) for the site-specific PMP Studies, studies have been completed on the Moose Creek, Bluestone and Whittier Narrows projects, and studies are in progress for the Martis Creek, Fort Peck, Garrison, and Kajaki projects; (3) the HEC-MetVue Tool is being developed to process storms by developing Depth-Area-Duration (DAD) relationships, isohyetal maps, and gridded precipitation estimates. It will also be used to rotate, transpose and maximize extreme storm data, and link the results to the USACE’s Data Storage System (HEC-DSS), and Hydrologic Modeling System (HMS). HMR 51/52 and the HMR55A plugins will be incorporated into the HEC-MetVue tool. The HMR 57 Tool is also used in extreme storm applications. A relatively new aspect is the use of atmospheric modeling to better understand extreme storms.

The development of the “Extreme Storm Database” is intended to provide a common database to be shared with all Federal and State agencies, academia, and private consultants. The database will include both historic (e.g., Extreme Storm Catalog and HMR storms) and future extreme storms, depth- area-duration tables, isohyetal maps, mass rainfall curves, meteorological characteristics of the storm event, radar data, and enabling interface with hydrologic models (e.g., HEC-RAS) and tools.

The Extreme Storm Database will incorporate information from the Extreme Storm Catalog developed by the USACE in cooperation with the U.S. Weather Bureau (USWB) and the U.S. Bureau of Reclamation (USBR).

Cover of Extreme Storm Catalog

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The catalog consisted of a two-page Pertinent Data Sheet for each of the extreme storms analyzed. The Pertinent Data Sheet contained summary information on the Part I and Part II storm studies conducted for each storm including approval dates by the USWB and USACE. Also included were summaries of the depth-area-duration tables, mass rainfall curves and isohyetal maps for each of the storms. More detail on each of the storms is contained in the Part I and Part II storm studies. Updates to the Extreme Storm Catalog with additional storm analyzed were published by USACE in 1962 and 1973. Some additional storms were analyzed by the USWB and USBR for inclusion in HMR55A, HMR57, and HMR58/59 but were not included in the USACE Storm Rainfall publication.

Sample Pertinent Data Sheet in Extreme Storm Catalog

The new Extreme Storm Database will include a "Data Archiving and Analysis System" which incorporates scanned images of original data collected from each storm event including the original ‘bucket survey’ forms, hand drawn isohyetal maps, and basic data collected from each storm event. This will allow the user to confirm the original data for each storm event. Also, the original isohyetal maps will be digitized into a GIS format for use in storm transposition studies and for computing depth area relationships. A schematic of the Data Archiving and Analysis System is shown below.

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Extreme Storm Database Data Archiving and Analysis Schematic

The database will also include additional extreme storms that have occurred since 1973.

A major addition to the database is the radar data for the storms. NWS radar data can be downloaded from the NWS at: http://dipper.nws.noaa.gov/hdsb/data/nexrad/nexrad.html .

Another source of precipitation estimates used by USACE is the Stage III precipitation data developed by the Hydrometeorological Analysis and Service (HAS) forecasters at the River Forecast Centers (RFC). Stage III data are derived from the Digital Precipitation Array (DPA) products, operational hourly rain gauge data, and interactive quality control by the RFC forecasters. USACE cooperates with the NWS and other Federal agencies at the various RFC across the U.S. Precipitation data used by USACE includes the Multisensor Precipitation Estimate (MPE) which is a combination of radar and actual precipitation gauge recordings. MPE is valuable for estimating precipitation in areas between precipitation record gauges.

The following table provides the time periods covered by the Stage III and MPE information for the 12 River Forecast Centers.

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Stage III MPE

ABRFC May 1993-Dec 2004 Jun 2003-Sep 2014

APRFC Jul 2002-Sep 2014

CBRFC Sep 1996-Mar 2002 Feb 2002-Sep 2014

CNRFC Sep 1996-Jan 2005 May 2003-Sep 2014

LMRFC Apr 1996-Aug 2003 Aug 2003-Sep 2014

MARFC Oct 1995-Dec 2001 Oct 1999-Sep 2014

MBRFC Nov 1994-Jun 2003 Jan 2003-Sep 2014

NCRFC Dec 1994-Apr 2002 Feb 2002-Sep 2014

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NERFC Feb 1996-Aug 2002 Aug 2002-Sep 2014

NWRFC Jan 1996-Nov 2002 Nov 2002-Sep 2014

OHRFC Dec 1995-Jun 2003 Dec 2001-Sep 2014

SERFC Dec 1995-Sep 2002 Jan 2002-Sep 2014

Table of Stage III and MPE information for the 12 River Forecast Centers

Recently the USACE began development of a prototype web site and database to aid in the initial development of the Extreme Precipitation Database. The web site will include electronic versions of the HMRs, site specific PMP studies, and other pertinent references for extreme storm studies that will be available for download. The layout, format and location of the web site for long term maintenance will be developed by the federal interagency Extreme Storm Events Work Group.

A sample screen shot from the existing web interface is shown below:

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Doug provided examples of how the June 9 – 10, 1972 Rapid City, SD storm and flood; and the September 9 – 16, 2013 storm in Colorado along the Rocky Mountain front in the vicinity of Boulder would capture the precipitation data, radar and storm characteristics. He identified the data sources for these and other extreme storm database analyses to be posted on the USACE Website: U.S. Storm Rainfall (1882-1973); Bucket Surveys (USACOE, USBR, NWS); NOAA COOP Observations (1753-2014); NWS Radar Estimates (1993-2014); CoCoRaHS (1998-2014); and local and regional precipitation networks (NERain, SD-AWDN, NDAWN, DOT, ALERT, etc).

He discussed the planned database enhancements which could include: a latitude/longitude search box or use of location and radius descriptors; identify the storm type (e.g., synoptic, convective, etc.); conditions on how non-USACE users could access (read-only, edit, add rights); identify who entered/edited data; provide an entire DAD Table; ability to search and interpolate any area or duration; plot DAD curves; show reference location on map; extract Dew Points from storm map; extract PMP from map; and compute % of PMP.

Doug discussed the HEC-MetVue code and how it is used to catalogue historic storms and apply synthetics storms. HEC–MetVue is an Arc GIS-based meteorological/visualization model which accepts Shapefiles in any coordinate system (e.g., precipitation, basin). The model utilizes “Drop and Drag” or menu driven options. Its inputs include: QPE, QPF (XMRG, NetCDF) and rain gage data (ASCII, DSS). Its outputs include: DSS Hyetographs/ Gridded Precipitation (HRAP,SHG). The model is used to analyze historic storms; compute DAD; translate, rotate, and maximize storms; calibrate QPE to gage data or PRISM data; and aggregate/segregate storms. HEC-MetVue is also used to develop Design Storms whether for Hypothetical Frequency Based or PMP based using estimates in HMR51/52, HMR55A, HMR58/59. The model provides linkage with HEC-HMS and the Extreme Storm Database.

Dr. Aaron Byrd discussed an ongoing project that focuses on enhancing the ability of USACE engineers to conduct extreme event hydrologic studies. This project is part of the Water Resources Infrastructure Technology (WRITe) research program. The overall goal of the project is to create tools and techniques that enable extreme event flow frequency analysis, including uncertainty in the models and extreme precipitation estimates. As an initial step, the work will focus on enhancing the HEC-MetVue code to easily incorporate extreme event estimates from the online NOAA Atlas 14 data. Subsequent stages of the work will focus on stochastic weather simulators to estimate extreme events as well as sequences of events, that may or may not be extreme events, which together make for extreme flow situations. Tools to quickly estimate extreme flows based solely on the historic flows will also be developed to give another check on the results. The results will be a tool that can conduct studies for a range of extreme flood flows based on extreme precipitation events and place those results in the context with other extreme flow estimates, including PMF estimates. The figure below shows the overall parts of the project and how they fit together.

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Overall picture of the proposed work for the WRITe extreme flow estimation work unit.

8. U.S. Bureau of Reclamation (BoR)

John England and Victoria Sankovich-Bahls, BoR discussed BoR’s needs in extreme precipitation data and methods. This information supports their risk analysis and dam safety program, specifically their hydrologic hazard analysis (HHA) hierarchy and levels of study with a focus on the Issue Evaluation (IE) extreme precipitation, and Corrective Action Study (CAS) extreme precipitation. They identified numerous opportunities in the development and analysis of extreme rainfall observations and databases. These include the coupling of point rainfall data with the significant use of radar data to provide better spatial and temporal correlations, and the need to establish and maintain a national extreme storm catalog. They also discussed opportunities to incorporate advances in statistics and data processing methods using regionalization techniques, storm spatial and temporal patterns, mapping larger regions, accounting for seasonal variability, and quantifying uncertainty estimates. They also discussed possible improvements in physical and numerical modeling through the use of radar data resulting in better resolution models for better results; the use of models for hypothesis testing; modeling to evaluate past events such as the September 1970 and May 2010 storms in the Nashville, TN area. Finally, BoR addressed the needs to handle technical complexities related to watershed size and different storm mechanisms; create and utilize evolving computing resources; training of skilled personnel to conduct hydrometeorological studies needed to update the HMRs and risk analysis.

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9. State Perspectives on Extreme Precipitation Uses in Dam Design Analyses

As discussed above under the Questionnaires heading of this Synthesis report, an Extreme Precipitation Needs questionnaire was distributed to State Dam Safety agencies. The State Needs questionnaire was developed by the Extreme Storm Event Work Group in support of the National Dam Safety Program, under which the Federal government supports State dam safety agencies to protect the public from dam failures.

During preparation of the State Needs questionnaire, Victor Hom and Tom Nicholson presented to the Interagency Committee on Dams (ICODS) and the National Dam Safety Review Board (NDSRB) on April 24, 2014 at their quarterly meeting, to inform them about the questionnaire prior to making an information request of the State agencies. ICODS and NDRSB requested that the ESEWG review FEMA P-919, Summary of Existing Guidelines for Hydrologic Safety of Dams (July 2012) to eliminate redundancy and minimize the burden on State respondents caused by the ESEWG questionnaire.

The Work Group reviewed FEMA P-919, specifically Section 9 Summary of Current State Hydrologic Design Guidelines, Section 10, Receptiveness of States to Changing Guidelines, and Appendix C, Hydrologic Safety of Dams Surveys. After review, the Work Group eliminated several redundant questions from their questionnaire, but in general determined the FEMA P-919 questionnaire dealt more generally with spillway sizing regulations, whereas the ESEWG’s questionnaire deals specifically with Extreme Precipitation needs of the States to help them enforce such regulations. The States Needs survey was developed with input from Mark Perry, State of Colorado Dam Safety Branch and ESEWG member, and based on consultation with other State Dam Safety agencies.

Victor Hom and Robert Mason distributed the States Needs questionnaire to numerous State agencies participating in the NDSBR. Mark Perry worked with the Association of State Dam Safety Officials (ASDSO) to distribute the State Needs questionnaire to remaining State Dam Safety agencies. Due to the need for multiple levels of communication prior to distribution of the State Needs questionnaire there was a relatively short turnaround for State respondents. The States Needs questionnaires were distributed between April 25, 2014 and May 1, 2014, and responses were requested by May 6, 2014. Nevertheless, a strong showing was made by State Dam Safety agencies with 21 States responding, namely: Arizona, California, Colorado, Connecticut, Idaho, Maryland, Massachusetts, Minnesota, Mississippi, Montana, Nebraska, New Mexico, New York, Oklahoma, Pennsylvania, Tennessee, Texas, Utah, Virginia, Washington, and Wyoming. The number and quality of State responses clearly communicated the importance of Extreme Precipitation Needs to State Dam Safety agencies. Following is an example State Questionnaire response:

6. Please discuss applicability of current Federal extreme precipitation publications, databases and tools:

a. Hydrometeorological Reports

xiv. Is updating the HMRs a priority to your State/agency? YES - AZ DWR considered updating of HMR-49 to be such a priority that it cost-shared with two dam-owning agencies and the State NRCS Office to independently fund 3-year, nearly $900,000 study to produce more reliable PMP depths for all regions of the State. AZ encourages the NWS to support the needs of its neighboring states, including Colorado, New Mexico, Nevada, CA and Utah by updating the woefully outdated HMR-49.

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All State questionnaires were reviewed by Mark Perry and Victoria Sankovich-Bahls prior to the ESEWG’s May 15, 2014 Workshop and were summarized for presentation to Workshop participants. The Workshop agenda was distributed to State Dam Safety agencies prior to the meeting, and they were invited to participate either on-site or remotely via webinar. Five (5) State agencies (AZ, CA, CO, AZ and PA) were asked to present results to the questionnaire in order to represent the nature of State Extreme Precipitation Needs.

During the May 15th Workshop, Mark Perry moderated a panel discussion of State Dam Safety officials. Mr. Perry began by thanking the ACWI SOH, ESEWG, ICODS, NDSRB, ASDSO, State questionnaire respondents, and FEMA for recognizing the importance of the States’ Extreme Precipitation Needs. He also qualified the States Needs summary by acknowledging that State Dam Safety agencies are independent and has unique needs; neither the ESEWG nor any Workshop participants claim to speak for all State agencies. With that qualifier, he presented the following general summary of State Extreme Precipitation Needs from the questionnaire (see Appendix D for a detailed summary of State questionnaire responses):

• Probable Maximum Precipitation (PMP) estimates are very important to the States; in most cases State spillway sizing regulations are based on NOAA Hydro-Meteorological Report (HMR) PMP. In some cases the requirement for States to use NOAA HMR PMP is codified in State statute. Around the year 2000 NOAA decided to no longer support its HMR PMP products, leaving the States in a difficult situation.

• Extreme Precipitation products included in the ESEWG’s proposal to the ACWI need to consider workload of the State, which is generally hundreds of dams per staff member. Detailed site specific hydro-meteorological studies for each dam are simply not practical.

• States need Extreme Storm products that are technically and politically defensible to private dam owners and State legislators. Currently NOAA HMRs developed in the 1970s and early 1980s are difficult for States to defend while trying to enforce spillway safety regulations that could cost dam owners millions of dollars in modifications.

• A nationwide Extreme Precipitation product would be good for the dam safety industry and may help make regulations more defensible, as opposed to the piecemeal approach to Extreme Precipitation products by individual States that is currently occurring.

• The importance of updated Extreme Precipitation products, specifically updated PMP estimates, is urgent. At least eight States have moved forward with individual Extreme Precipitation or PMP studies in the absence of Federal action and more States are considering it. In some States the level of opposition to the outdated and unsupported NOAA HMR PMP has risen to the political level with one State legislature reportedly threatening to place a moratorium on its Dam Safety agency until the issue is resolved.

Mr. Perry highlighted the following specific State questionnaire responses:

• HMR 49, which covers parts of the Western U.S. including the Colorado Plateau and Great Basin States was published in 1977 and did not use modern PMP methods. The State of Arizona recently completed its own Statewide PMP updated study; their questionnaire response states that their 2008 study “concluded that PMP depths published in HMR 49 are outdated, unreliable, and not supported by data” and “the State of Arizona does not rely on PMP depths published in HMR 49 and discourages its continued use for other states.”

• HMR 51 & 52 need to be updated due to their large areal coverage of the eastern U.S. • States regulate many small dams, often with small drainage areas (<100 square miles).

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• States have seen an increase in Site Specific PMP (SSPMP) studies due to the outdated and unsupported NOAA HMRs. SSPMP studies put a burden on understaffed State Dam Safety agencies, which typically do not have in-house meteorological experts.

• Outdated and unsupported NOAA HMRs make it politically difficult for States to regulate spillway size

• Regarding questions about use of Risk-based Extreme Precipitation Products: Some States expressed doubts about whether risk can be determined accurately

for extreme hydrologic events Some States questioned the practicality of risk-based methods in light of

continually increasing development below many dams (so called, “hazard creep”) States may be constrained to use PMP, PMF, and specifically “NOAA HMR”

PMP estimates by State statute, code, or regulations. States may be receptive to a Risk-based Extreme Precipitation Product if it is

accompanied by clear Federal guidelines on how to apply it to spillway sizing. Following Mr. Perry’s summary of States’ Extreme Precipitation Needs, the following State panelists discussed their State-specific needs and questionnaire responses:

1) Michael Johnson, PhD, P.E., Arizona Department of Water Resources (by webinar): The State of Arizona, Division of Water Resources, Dam Safety Section commissioned a 2008 study by Applied Weather Associated LLC and Metstat Inc. that concluded HMR 49 PMP estimates are outdated, unreliable and not supported by data. The State of Arizona does not rely on HMR 49 PMP estimates and discourages the use of HMR 49 by other States. Arizona DWR considered updating HMR-49 to be such a priority that it cost-shared a Statewide PMP update study along with the NRCS. The study cost was $900,000 and duration was three years.

The Arizona PMP Study was performed by Applied Weather Associates with review by various State and Federal Agencies. A companion report is publically available at the Arizona DWR website: http://www.azwater.gov/AzDWR/SurfaceWater/DamSafety/

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The 2013 AZ DWR study included development of a publically-available GIS-based application (ESRI add-on) for computation of basin-specific PMP depths for any user-defined drainage area within the State:

http://www.azwater.gov/AzDWR/SurfaceWater/DamSafety/DamSafetyTechnicalReferences.htm

Fifty-one extreme rainfall storm events were identified during the Arizona PMP Study, having rainfall centers with similar characteristic to extreme rainfall events that could control PMP values at locations within our state. This included 12 general winter storms, ten remnant tropical storms, and 29 local convective storms. Each of the 51 storms was analyzed using the Storm Precipitation Analysis System, which produced Depth-Area-Duration (DAD) values, mass curves, and total storm isohyetals. NEXRAD data was incorporated when available. NOAA Atlas 14 precipitation frequency data was used to calculate the Orographic Transposition Factor. HYSPLIT model trajectories and Sea

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Surface Temperature (SST) data from NCAR and NOAA were also used in the storm adjustment processes. To house, analyze, and produce results from the large data set developed in the study, the PMP Evaluation Tool was developed. This tool uses a combination of Excel and GIS to query, calculate, and derive PMP values for each grid cell, for each duration, and for each storm type. For local convective storms, the durations analyzed were 1-, 2-, 3-, 4-, 5-, and 6-hours. For remnant tropical and general winter storms, the durations analyzed were 6-, 12-, 18-, 24-, 48-, and 72-hours. The figure to the right shows Local Storm 6-hour PMP estimates at 10 mi2 resolution for the entire State.

Arizona DWR supports national guidelines for Extreme Precipitation Products but not national standards, stating that no single national standard would result in consistent levels of risk when applied to the range of human development and meteorological hazards across all fifty states.

Arizona DWR encourages the National Weather Service (NWS) to support the needs of California, Colorado, New Mexico, Nevada, and Utah by updating HMR 49.

2) Ronald Mease, P.E., Pennsylvania Department of Environmental Protection, Division of Dam Safety (on-site participant): Pennsylvania Division of Dam Safety understands that HMR 51 PMP estimates may be high due its handling of the extreme rain event at Smethport, PA, in the 1940s. High PMP estimates (generally about 36 inches in 24 hours) make it difficult for dam owners to comply with PA dam safety regulations for spillway sizing. Because the NOAA HMRs are outdated and unsupported, it makes it hard for State regulators to convince dam owners that spillway improvements are needed.

PA Dam Safety Regulation Chapter 105, Section 105.98, uses the Probable Maximum Flood (PMF) as the basis for spillway sizing; the regulations define PMF as being “derived from the probable maximum precipitation (PMP) as determined on the basis of the most recent data available from the National Oceanographic and Atmospheric Administration (NOAA).”

PA Dam Safety is holding discussions with meteorological consultants about performing a Statewide PMP update study (similar to what was done in Arizona and at least seven other states); however, funding and regulatory constraints need to be resolved.

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Specifically, Regulation Section 105.98 would need to be changed to remove dependence on NOAA HMRs.

PA Dam Safety recently changed its regulations to require Incremental Damage Analysis for spillway sizing, which is a form of risk analysis. Their concern with using a true risk-based extreme precipitation product is that they regulate nearly 800 high hazard dams; so any new risk-based spillway sizing procedure would need to be simple to apply. It would also require changes to State regulations, for which it would be beneficial to have Federal guidelines.

Finally PA Dam Safety said it would be helpful to have a web-based PMP tool similar to the USGS Stream Stats, which could delineate a drainage basin and calculate the PMP hyetograph for the user. They cited the difficulty of applying HMR 52 and said they currently have to rely on an outdated MS DOS program to run HMR 52.

3) Robert Bennett, P.E., R.A., C.F.M., Virginia Department of Conservation & Recreation (by webinar): In 2008, Virginia Dam Safety began a program requiring dam owners to create or update dam breach inundation mapping. That effort exposed many cases of increased hazard potential due to recent downstream development (so called “hazard creep”) and the need for increased hazard classification at many dams, which in turn resulted in increased spillway size requirements for those dams. There was political opposition from dam owners to the increased spillway size requirements. In response Virginia Dam Safety incorporated Incremental Damage Analysis and other alternatives into its regulations for spillway sizing. Nevertheless going into the commonwealth’s 2014 legislative session, three Virginia legislators were proposing legislation to put the Dam Safety program under a moratorium until the spillway sizing issue could be resolved. The Dam Safety agency was able to negotiate a solution whereby a Statewide PMP study would be performed to replace NOAA HMR 51 and obtain modern, defensible PMP estimates; the Virginia Legislature funded the PMP update study. A contract was awarded to Applied Weather Associates, LLC (also performed the Arizona PMP update study) and has a Dec. 1, 2015, delivery date. Virginia Dam Safety is assembling a board of consultants to review their Statewide PMP update study and expressed their interest in Federal agency participation.

Regarding risk-based approaches, Virginia Dam Safety has discussed it internally but does not have any plans to implement regulations based on risk. The biggest need for them is updated PMP.

4) Melissa Collord, P.E., California Department of Water Resources, Division of Safety of Dams (by webinar): California Division of Safety of Dams (CA DOSD) explained their partial risk-based method for spillway sizing, whereby the design rainfall varies between the minimum 1000-YR Average Recurrence Interval (ARI) and PMP, depending on the hazard classification of the dam. CA DOSD has traditionally used frequency storm data compiled internally, but has recently began allowing use of NOAA Atlas 14.

CA DOSD expressed concern that they are receiving more Site Specific PMP studies for spillway sizing and attributes it to outdated and unsupported NOAA HMRs. They explained the burden SSPMP studies put on State agencies, which typically do not have in-house meteorological expertise. CA DOSD recently rejected a SSPMP study

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performed by Applied Weather Associates LLC, which was performed under FERC Part 12 D. CA DOSD believes updated NOAA HMRs would preclude the need for most SSPMP studies.

CA DOSD made the point that a national Extreme Precipitation product and Federal guidelines would benefit dam owners who are regulated by both CA DOSD and the Federal Energy Regulatory Commission (FERC). Without a Federally supported product, such dual-regulated dam owners may be in a position where a State adopts new PMP estimates, but FERC does not accept the State study.

Regarding Risk-based Extreme Precipitation products, CA DOSD considers risk-based approaches to be complex and believes they are generally not valuable because of very large uncertainties in computing extreme precipitation and runoff at the large return intervals needed for risk analysis. They suggest that any risk-based Extreme Precipitation product needs to include an understanding of uncertainty. They do use a simplified risk-based spillway sizing method (described above).

CA DOSD pointed out that they do not use percentages of PMP to design spillways, as the resulting values may vary in terms of probability of occurrence. FEMA P-919 noted that many State dam safety agencies currently allow use of percentages of PMP (e.g. 50% PMP for a Significant Hazard Dam), and the FEMA report recommends discontinuing this practice.

Finally, CA DOSD is currently updating its procedures for hydrologic analysis and is very interested and supportive of the efforts being undertaken by the ESEWG.

5) Mark Perry, P.E., Colorado Division of Water Resources, Dam Safety Branch (on-site participant): The State of Colorado Dam Safety Branch (CO DSB) has a long history of trying to improve PMP estimates at high elevations and in mountainous terrain. Following is an abridged list of CO DSB efforts:

• 1984: CO DSB questions the applicability of NOAA HMR 55 at high elevations, at least in part contributing to release of the revised report, HMR 55A, which allowed a greater elevation reduction for PMP Local Storms.

• 1989: CO DSB hosted a Workshop on Hydrologic Aspects of Dam Safety at Colorado State University to elicit expert discussion on high elevation extreme precipitation. (The workshop report reference is included at the end of this Synthesis report).

• 1997: CO DSB funded the Extreme Precipitation Data Study by Colorado State University Atmospheric Science Dept (CSU), which resulted in the publication of Climatology Report 97-1 (see References).

• 1999-2003: CO DSB funded numerical modeling study by CSU using their Regional Atmospheric Modeling System (RAMS) to develop a new method to estimate PMP in mountainous terrain (see References). In the end, the CO DSB decided not to pursue the numerical modeling method, likely because it was perceived as being too theoretical for regulatory purposes.

• 2005-2008: CO DSB contracted with HDR Engineering Inc. to develop a GIS-based Site Specific PMP program that became known as the Extreme Precipitation Analysis Tool (EPAT). The main contributions of EPAT were to be incorporating recent extreme rain events and NEXRAD data into the storm database, limiting storm transposition limits in mountainous terrain based on climate zones identified in CSU Report 97-1, and eliminating the HMRs reliance

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on the complicated Storm Separation Method to account for orographic forcing. The following figures show storm analysis in EPAT, EPAT Climate Zones, and an example storm in EPAT’s GIS storm library.

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EPAT Storm 34 (Pueblo/Penrose 1921) from EPAT’s GIS storm library.

• 2013: The CO DSB completed Phase II of a quality control & independent meteorological evaluation of EPAT performed by Applied Weather Associates, LLC. Unfortunately the study found EPAT to be plagued by numerous errors (e.g. in-place maximization factors), inconsistencies (e.g. different durations used for storm reference dew points vs. maximum persisting dew points), unsupported deviations from NOAA HMR and WMO PMP procedures (e.g. barrier elevations were not accounted for in the storm transposition process), and unsupported deviations from the state of the practice (e.g. the narrow storm transposition limits are not supported by current meteorological knowledge).

• 2014: Based on results of the EPAT Phase II study the CO DSB is no longer using EPAT. Due to studies in neighboring states showing inadequacy of NOAA HMRs, specifically HMR 49, CO DSB is at a decision point and is considering whether to move forward with a Statewide PMP update study similar to that completed by Arizona and at least 7 other states.

CO DSB cited specific possible improvements for PMP estimates at high elevations & mountainous terrain that should be addressed in new Extreme Precipitation products:

• Better understanding of storm transposition limits based on physical processes, possibly numerical modeling, at work in mountainous terrain.

• Better elevation adjustments for General and Local storms (see discussion above about the revision made between HMR 55 and HMR 55A)

• Better aerial reduction factors based on actual storm data at high elevations and in mountainous terrain

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• Finer resolution analysis to account for topographic barriers to moisture supply in highly variable mountainous terrain

Finally, CO DSB listed some of its specific Extreme Precipitation Needs:

• HMR 49 update • Modern, improved methods for Extreme Precipitation estimates at high elevations

including numerical modeling, paleo-hydrology, etc. (reference “Estimating Bounds on Extreme Precipitation Events: A Brief Assessment”, National Research Council, 1994)

• Guidelines for Site Specific PMP Studies (CO regulations currently allow Site Specific PMP studies for spillway sizing, but CO has no guidelines for such studies. FEMA P-919 indicates that CO is not alone in the situation).

• CO DSB may be open to using Risk-based Extreme Precipitation products if they are accompanied by Federal guidelines on how to apply them to spillway sizing and are simple to use in light of our large number of regulated dams per staff person.

• Risk-based methods could help CO address the perceived disparity between urban and rural dams under current prescriptive approaches to spillway sizing, and could help us prioritize many needed repairs in the aging inventory of regulated dams.

Following the above State panel presentations; opportunity was provided for comments by other States participating remotely by webinar, namely Kentucky, Montana, and New Mexico dam safety agencies. Mr. Shane Cook of Kentucky, Division of Water, explained that Kentucky statute specifically requires use of NOAA HMR PMP for spillway sizing. Kentucky Dam Safety would like to pursue their own PMP update study, but they are caught in a regulatory dilemma: they cannot get funding for a PMP update study that cannot be used under current state statute, but at the same time the statute cannot be changed to allow use of a PMP update study that does not yet exist. Mr. Cook welcomed any feedback from other States that have dealt with this problem. Finally, at least eight States have completed PMP update studies performed by consulting meteorologists, reviewed by boards of Federal and State experts, and funded by consortiums of State governments, regulatory agencies, and dam owners. Mr. Perry suggested these States have demonstrated an effective model for updating PMP. Possible problems to be solved are that no consistent PMP study guidelines exist, there are a limited number of meteorological consultants performing the work, and boundary issues between States exist. As a solution to these challenges, Mr. Perry proposed Federal oversight of the statewide PMP update process including the following:

• Cost-share grant program to the States for PMP update studies through FEMA’s National Dam Safety Program, similar to funding mechanism of NOAA Atlas 14

• Create Federal guidelines for Statewide PMP studies that would be a condition of Federal grants and would allow Federal agencies to accept Statewide studies

• Procedures for dealing with boundary issues between States • A grant program may help generate interest by more meteorological consultants

Conclusions and Recommendations

Victoria Sankovich-Bahls, workshop facilitator summarized the candidate products identified during the workshop presentations and discussions as:

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• U.S. Extreme Precipitation Database (including its long-term maintenance and hosting) to include electronic archiving of storm paper records that were the basis of the HMRs;

• Extreme Precipitation Estimates beyond 1:1,000-year (also known as the “Extreme Precipitation Analysis Tool”);

• Completion of NOAA Atlas 14 (not beyond 1:1,000-year);

• Streamlined Updating of PMPs using statistical methods (workshop is recommended to fully develop);

• Interagency business process to analyze after-event data (an example would be the tornado damage assessment process as a model) tie to the Extreme Storm Catalogue; and

• Synthesis of workshop discussions on needed products.

References:

Cotton, William R., Development of New Methodologies for Determining Extreme Rainfall, Final Report for Contract ENC #C154213, State of Colorado Department of Natural Resources.

Doesken, N. and Thomas McKee, Colorado Extreme Storm Precipitation Data Study, Climatology Report #97-1, Colorado State University Dept. of Atmospheric Science, May 1997.

Federal Energy Regulatory Commission, Engineering Guidelines for the Evaluation of Hydropower Projects, Washington, DC, June 28, 2010, https://www.ferc.gov/industries/hydropower/safety/guidelines/eng-guide.asp

Hydrologic Aspects of Dam Safety, Report of Workshop held on November 16, 1989, Ed. Neil S. Grigg, Colorado Water Resources Research Institute, Information Series No. 62.

Natural Resources Conservation Service, NRCS Technical Release (TR) 60 “Earth Dams and Reservoirs,” Washington, DC, July 2005 http://directives.sc.egov.usda.gov/OpenNonWebContent.aspx?content=24937.wba

Tomlinson, Edward M., William D. Kappel, Michael Johnson, Tye Parzybok, Douglas Hulstrand, Arizona Statewide Probable Maximum Precipitation (PMP), Improving HMR 49, http://www.appliedweatherassociates.com/uploads/1/3/8/1/13810758/arizona-statewide-probable-maximum-precipitaiton-improving-hmr49.pdf

U.S. NRC, “Standard Review Plan for the Review of Safety Analysis Reports for Nuclear Power Plants: LWR Edition,“ NUREG-0800, U.S. Nuclear Regulatory Commission, Washington, DC, July 14, 2014 http://www.nrc.gov/reading-rm/doc-collections/nuregs/staff/sr0800/

U.S. NRC, “Design Basis Floods for Nuclear Power Plants”, Regulatory Guide 1.59, U.S. Nuclear Regulatory Commission, Washington, DC, 1977

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Appendix A: Federal Agency Questionnaire

Appendix B: Summary of Questionnaire Reponses by Federal Agencies

Appendix C: State Dam Safety Agency Questionnaire

Appendix D: Summary of Questionnaire Responses by State Dam Safety Agencies

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APPENDIX A

Advisory Committee on Water Information (ACWI) Subcommittee on Hydrology (SOH)

Extreme Storm Events Work Group (ESEWG)

Federal Agency Questionnaire for Needs in Extreme Precipitation

Preamble: Extreme storm hydrometeorology studies impact extreme flood estimates and assessments for dams, nuclear power plants, levees, and other high-hazard structures within the United States. Additionally, environmental impacts from extreme storm events are of increasing concern. The Extreme Storm Events Work Group is responsible for reviewing and improving methodologies and data collection techniques used to develop design precipitation estimates of large storm events up to and including the Probable Maximum Precipitation. The charter for the Work Group states that it will develop a detailed scope of work/plan of study and determine the necessary funding requirements to update the Catalog of Extreme Storms and Hydrometeorological Reports (HMRs). The Work Group is also tasked with developing a list of individual Federal Agency extreme storm product needs. From ongoing discussions and recent advances to probabilistic methodologies for risk-assessment, it is evident that updates to the Catalog of Extreme Storms and Hydrometeorological Reports may not fully address the national needs. This questionnaire asks each Agency to critically evaluate their views, methods, data sources, tools, etc. regarding extreme storm events and to identify any needs and/or gaps in extreme storm event information. In a Writing Workshop scheduled for later this year, the answers to the questionnaires will be synthesized to define extreme storm product(s) that are needed for deterministic and risk-informed infrastructure design. The product(s) and corresponding schedule(s) and cost(s) will be presented in a proposal to ACWI-SOH.

1. Discuss your agency methods and extreme precipitation needs for decision making,

assessments, and designs (extreme precipitation is defined as those events with a return period of 1,000-years or greater, up to and including PMP):

a. What extreme precipitation data do you use in your decisions? b. How is this extreme precipitation data used? c. What is the scale and resolution of this data (regional, site-specific, watershed-specific)? d. What is the spatial extent to which this data is applied? e. Would it be beneficial if this data were updated? And why is that? f. What decisions are made by utilizing this data?

2. Describe your agency views on the recommendations and priorities from “Estimating Bounds on

Extreme Precipitation Events” NRC 1994 report (pp 19-21), including: http://www.nap.edu/openbook.php?record_id=9195

a. Continued use of PMP, or alternatives? b. Use of Numerical models? c. Assessment of radar accuracy?

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d. Estimating probabilities of extreme rainfall? e. Storm-based analyses? f. Is there a need for a national standard for consistency?

3. Discuss your thoughts and views on the priorities (risk analysis, standards, meteorology) from

the “Hydrologic Research Needs for Dam Safety” FEMA workshop USACE 2001 report (pp. 171-176) (also published by FEMA in 2005), including these three from the top 10: http://www.hec.usace.army.mil/publications/SeminarProceedings/SP-29.pdf

a. Historical database of storms and floods? b. Precipitation Analysis needs? c. Extend frequencies?

4. Describe what your agency would like to incorporate and support that came out of the

Probabilistic Flood Hazard Workshop held at the Nuclear Regulatory Commission in January 2013 http://www.nrc.gov/reading-rm/doc-collections/nuregs/conference/cp0302/ (pp. 10-4 to 10-7)

a. Focus on extreme rainfall observations and improve databases b. Explore advances in data-processing methods c. Develop regionalized techniques d. Stochastic methods

5. Discuss applicability of current Federal extreme precipitation publications, databases and tools:

a. Hydrometeorological Reports i. What information do you glean from the HMRs? And how do you use this

information exactly? ii. Which information is most useful?

iii. Do you use the spatial and temporal storm patterns provided? iv. Do you use the DAD tables? v. Do you use the HMRs to compute PMP?

vi. Do you use the HMRs to compute a percentage of PMP? Which percentage? vii. Do you use the areal reduction factors provided in the HMRs?

viii. Do you consider storm seasonality in your studies? ix. Which HMR do you consult the most often? x. Are the HMRs easy to use? If not, why?

xi. Do you use the digitized HMR 51 plates? Or the shapefiles available for HMR 58 and 59?

xii. What would you change about the HMRs when/if updated? xiii. What additional information would you want to see included? xiv. Do you use any other studies besides the HMRs for PMP? xv. Do you estimate PMP probabilities? If so, how?

b. NOAA Atlas 14 i. NOAA Atlas 14 is being updated to include the Northeastern states (from TP40).

Funding has not yet been found to update estimates for Texas (from TP40) or

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the Northwestern states (from NOAA Atlas 2). How important is it to your organization to have NOAA Atlas 14 volumes for Texas and the Northwestern states?

ii. What information do you glean from NOAA Atlases 2 and 14? And how do you use this information exactly?

iii. Which return period is most useful to your studies? iv. Do you extrapolate beyond the 1,000-year return period (not recommended by

NWS)? If so, how? v. Which duration(s) is most useful to your studies?

vi. How do you determine your storm duration(s)? vii. NOAA Atlases 2 and 14 contain point-based precipitation. Do you need areal

information? viii. Do you currently compute areal estimates based on the point values from NOAA

Atlas 2 or 14? If so, how? And where/how do you obtain your areal reduction factors if you use that method?

ix. Which region of the United States is of most interest to you for precipitation frequency estimates?

x. Did you use NOAA Atlas 2 or TP40 before NOAA Atlas 14 volumes were published?

xi. Do you still use NOAA Atlas 2 or TP40? Where for? And for what purpose? xii. To what extent is NOAA Atlas 14 information incorporated into design guidance

or regulations that govern what you do? xiii. Are there elements in NOAA Atlas 2 or TP 40 missing in NOAA Atlas 14? xiv. Is NOAA Atlas 14 easy to use? How could it be improved? xv. Do you input latitude/longitude values into the web interface?

xvi. Do you consult the isopluvial maps of precipitation frequency estimates for a particular exceedance probability and duration? If so, what value do they provide beyond the GIS compatible grids of the same information?

xvii. Of what value are the temporal distribution curves in NOAA Atlas 14? xviii. Of what value are the seasonal curves in NOAA Atlas 14?

xix. There is a difference between precipitation frequency estimates more frequency than about 15-20 years ARI for estimates derived from annual maximum series and estimates derived from annual maximum series and estimates derived from partial duration series. How important is it for NOAA Atlas 14 to provide both? Which of the two is your preference and why?

xx. Do you consult the report documentation of NOAA Atlas 14 for any purpose? xxi. Do you use any of the background information that the NWS used to compute

the precipitation frequency estimates? If so, what exactly? (e.g., gauge data, clusters)

c. National Storm Catalog (USACE big black book of storms) i. Do you have a copy of this book?

ii. What information from this book do you use? iii. If the book was digitized, would you use the information?

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iv. Do you consult DAD tables in your safety analyses? v. Are storm spatial patterns needed in your safety analyses?

6. What other extreme precipitation resources does your agency utilize?

a. Non-Federal technical documents on extreme storms or PMP? b. Other non-Federal documents? c. Data? d. Software?

7. Discuss any gaps or further needs

a. What precipitation/extreme storm information do you need that you don’t have now? b. For data gaps, what is the most pressing piece of information that needs to be created

or updated?

8. Please identify Agency representatives and other attendees willing to participate in the Extreme Storm Events Work Group’s Writing Workshop, currently scheduled for May 15-16, 2014, in Washington, D.C., either on-site or remotely via webinar. Please include contact information.

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APPENDIX B

Summary of Questionnaire Responses by Federal Agencies

1 Discuss your agency methods and extreme precipitation needs for decision making, assessments, and designs (extreme precipitation is defined as those events with a return period of 1,000‐years or greater, up to and including PMP):

NRC: US NRC uses a “risk-informed” regulatory framework, although the manner and degree to which risks due to natural hazards are quantified varies. For example, the agency has used probabilistic seismic hazard analysis form many years. However, analysis of flooding hazards submitted for licensing of new facilities is almost entirely deterministic. Deterministic analysis via progressive refinement of conservative assumptions (called Hierarchical Hazard Assessment (HHA)) is commonly used. Concepts such as PMP and PMF are commonly used. On the other hand, a more explicitly risk-informed significance determination process (SDP) is being used for decision-making in light of new information that comes up after initial licensing. The SDP activities have often included attempts to quantify risks due natural hazards such as extreme precipitation and flooding.

More and more, applicants and licensee are submitting probabilistic flooding hazard assessments. US NRC is currently developing a research plan aimed at providing the technical basis for development of regulatory guidance for probabilistic flood hazard assessment (PFHA), including extreme precipitation. The goal is to develop an overall PFHA framework that can be used in both licensing and oversight activities.

NOTE-1: The types of sites and facilities for which extreme precipitation estimates are needed is varied: 1) nuclear power plant sites; 2) fuel cycle facilities; 3) interim spent fuel storage facilities; 4)nuclear waste repositories; 5) watersheds in which facilities are located; 6) reservoirs and dams upstream of nuclear facilities; and 6) tailings dams.

NOTE-2: The main question as written above appears predicated on cutting estimates off at the PMP. This does not seem to be compatible with a true probabilistic assessment.

NOTE-3: Many of the questions below refer to extreme precipitation “data”, when, in reality, the values in question are model-based estimates derived from actual data. We sometimes use these estimates as if they are data, but one should not lose sight of the fact that they are estimates with considerable uncertainties. Methods applied to develop estimates from the actual data and attendant uncertainties need attention too.

NOTE-4: Many of the sub-questions below seem to be targeted at deterministic approaches. While advances in deterministic approaches may be usefully applied to current NRC methods, it’s not the direction in which the agency is headed.

NWS: NOAA NWS generally isn’t a user of this information. Rather, historically, we’ve created it for the users and we’ve made the key documents available to users.

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1a What extreme precipitation data do you use in your decisions?

FERC: HMR based PMPs, site-specific PMPs, and NOAA Atlas 1000-yr 72hr values.

USACE: Probable Maximum Precipitation is used to develop the Inflow Design Flood for the design of spillways at USACE Dams. Dam safety studies require an estimate of the reservoir stage frequency curve defined out to the PMP/PMF event. One method for defining the frequency curve is rainfall-runoff simulation. Tools are being added to USACE software to sample precipitation data in a Monte Carlo analysis and then run hydrologic and reservoir models. Both estimates of magnitude and hyetograph temporal pattern are required. We use the HMR’s along with site-specific studies to define the Probable Maximum Precipitation. Site specific studies require extreme historical storms to be transposed over a watershed. Sources of data include NOAA, USACE, USGS and CoCoRAS. Flood risk reduction project studies typically require precipitation frequency data from the 2-year to 500-year event. We typically use NOAA data from NOAA-14, NOAA 2, TP-40 and HYDRO-35 for this information.

USBR: Reclamation uses point and basin-average precipitation frequency relationships with AEPs ranging from 10-3 to 10-7, up to and including PMP. Spatial and temporal extreme storm patterns are used to distribute the extreme storm precipitation over specific watersheds.

NRCS: PMP, NOAA Atlas

TVA: PMP data published in: HMR-41 (1965) for the Tennessee River Basin above Chattanooga; HMR-47 (1973) for Tennessee River basins above Wheeler and Kentucky Dams; and HMR-56 (1986) for watershed areas up to 3000 mi2. In addition, TVA uses PMP estimates prepared by the National Weather Service in special studies conducted in the early 1980’s for the watersheds above Douglas Dam (4541 mi2) and Cherokee Dam (3428 mi2).

TVA is currently funding a study being conducted by Applied Weather Associates to generate site specific estimates of PMP for a long list of critical watersheds in the Tennessee River Valley.

NRC: Consistent with US NRC’s Hierarchical Hazard Assessment (HHA) approach and Standard Review Plan (SRP), US NRC relies primarily on the PMP data “product” represented by HMRs. However, US NRC is increasingly faced with licensee reports that involve site-specific PMPs for flood hazard re-evaluations at existing nuclear power plants that are currently underway [1]. In addition, US NRC has a risk informed regulatory framework and reviews of probabilistic flood hazard assessments (PFHA) are expected as part of flood hazard re-evaluations at some existing sites. Currently available precipitation data and “data products” does not readily support probabilistic approaches for extremely rare events or for reviews of site specific PMPs (both basin-wide and for highly localized flooding). It should be noted that both issues require greater focus on the probabilities associated with the PMPs in both the HMR and site-specific PMP studies. Site-specific PMP estimates are sometime considerably lower than values in the HMRs which naturally raises the question of the level of conservatism implied by earlier and new proposed estimates.

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Loads on structures due to liquid and solid precipitation are derived from PMPs obtained from the HMRs.

The SDP activities have also included used of precipitation frequency estimates from NOAA Atlas 14 (or precursors).

[1] SECY‑11‑0124, “Recommended Actions to be Taken without Delay from the Near-Term Task Force Report,” and SECY‑11‑0137, “Prioritization of Recommended Actions to be Taken in Response to Fukushima Lessons Learned”.

USGS: The most common extreme precipitation data that is used by the USGS is the 24-hour, 2-year precipitation and other similar depth-duration-frequency information, commonly obtained from NOAA Atlas 14, although some local and regional studies of depth-duration frequency of precipitation have be completed by USGS programs.

1b How is this extreme precipitation data used?

FERC: Used to estimate PMP and resulting PMF.

USACE: The extreme precipitation is used along with hydrologic modeling simulations to determine design floods for our reservoirs and levee projects.

USBR: Data are used as input to rainfall-runoff models.

NRCS: Flood hazard studies; Auxiliary spillway and Freeboard design storms for small watershed dams

TVA: PMP data are used to drive hydrologic simulations to define design basis flood levels at dams and various other critical locations such as nuclear power plants.

NRC: In new reactor licensing extreme precipitation estimates (generally PMPs) are used to construct extreme flood scenarios. Two typical scenarios are: 1) the probable maximum flood (PMF) for stream and river flooding; and 2) local intense precipitation (LIP) for evaluation of site drainage. These scenarios are applied within the HHA approach outlined above.

PMP values from the HMRs are also used to determine design basis loads on structures due to both liquid and solid precipitation.

The SDP activities have also included used of precipitation frequency estimates from NOAA Atlas 14 (or precursors). The focus here is on estimating the frequency of an initiating event. The initiating event frequency is combined with system fragility information to evaluate risk.

USGS: These data are used as precipitation or weather indices in USGS regional regression equations that link basin characteristics data to estimates of flood frequency quintiles.

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1c What is the scale and resolution of this data (regional, site‐specific, watershed‐specific)?

FERC: Watershed-specific or site-specific

USACE: Multiple scales are necessary due to the various sizes of the watersheds being evaluated.

USBR: For moderate to detailed assessments, site-specific and watershed-specific information is developed. Regional information is used for PMP (HMRs) and depth-area relationships for screening-level assessments.

NRCS: Watershed specific; Site-specific if available

TVA: Watershed specific, although watershed sizes range from less than 100 mi2 to over 25,000 mi2. In addition, for nuclear plant site local drainage studies, PMP estimates for 1 mi2 areas are used.

NRC: The scale and resolution of “data” from the HMRs vary from very large watersheds (thousands of square miles) for river flooding down to 1-mi2 for evaluation of site drainage.

Licensees are also submitting “site-specific” PMP estimates for both large and small area sizes.

USGS: Watershed specific.

1d What is the spatial extent to which this data is applied?

FERC: Drainage areas associated with a dam.

USACE: The spatial extent is the watershed being modeled. Required information is area-reduction information. Typically, extreme historic storms are used to develop area-reduction factors.

USBR: Watershed scale, from point to > 10,000 mi2, usually at 4km2 or finer cell size. Custom information is developed for nearly all watersheds exceeding this scale.

NRCS: Drainage area above dams and below dams to assess effects of dams on downstream areas, flood hazard areas

TVA: For a given watershed, PMP is typically assumed to be centered over that watershed, with concurrent rainfall on adjacent watersheds also being considered and analyzed as necessary. Fixed patterns which define the spatial orientation of PMP for larger watersheds are used when specified in a given HMR.

NRC: Application falls under two categories: 1) LIP (local intense precipitation) on a resolution can be a small sub-watershed or even as small as tens of acres (approaching point precipitation) and 2) basin-wide riverine flooding and dam failure flooding for upstream

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watersheds. This latter can have a spatial extent that varies dramatically sometimes going well beyond the area sizes in the NWS HMRs.

USGS: The data are used in regionalization work done at the state level for every state, but have been shown to be highly significant in only 18 states.

1e Would it be beneficial if this data were updated? And why is that?

FERC: Yes. Updating the HMR’s would be beneficial to the dam engineering community. Potential changes to PMP values may impact the hydrologic safety and adequacy of the nations’ high and significant hazard potential structures. An additional benefit would be unbiased and uniform PMP values developed by the NWS.

USACE: Yes, Up to date data means precipitation frequency estimates contain recent historic storms. This data should be updated periodically.

USBR: Yes, it would be beneficial if the data bases used for the regional information were updated. In this way, data for magnitudes and probabilities used in site-specific and watershed-scale estimates could be improved. Regional extreme estimates would also be improved, by updating the data and including uncertainty estimates.

NRCS: Yes. Current HMR data is dated. NRCS criteria allows the use of special site-specific PMP studies, however, having updated PMP would, in many cases negate the need for special studies and greatly expedite design and decision-making processes.

TVA: TVA design basis flood levels are based on rainfall databases and meteorologic analyses that are now approaching 50 years old. TVA believes regular updates to PMP estimates and extreme rainfall in general would be beneficial to state and federal agencies and to the engineering community.

NRC: Yes, an update to the HMRs, and particularly HMR51, which applies to the majority of our sites would be beneficial. The HMRs referenced in our general guidance documents are often criticized due their limitations on basin size, questionable applicability in “stippled” regions affected by orographic effects, by their lack of consistency in methodology, and generally by their age. We are currently being requested to review site-specific PMP values on an increasing basis creating a regulatory challenge. In addition to “updating” the data with new storms, radar related data and rigorous review of previous storms, more focus on the probabilities associated with PMP estimates is a critical component to risk informed decision making. Any update should include a review of potential storm model improvements that could be used to improve both “updates” to values and additional probabilistic analysis of the updates. Just plugging new data into an old method without considering adjustments to that method based on decades of experience (since the last update of the HMR 51-52, for example) doesn’t seem appropriate. It’s also important start thinking about probabilistic characterization as an essential element of such extreme precipitation estimates.

Additional attention to cool season precipitation would be useful for determining design basis snow and ice loads on structures.

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USGS: The extreme precipitation data are used in regional regression equations that often yield estimates of flood frequency qualities used by many states in the design of routine transportation infrastructure such as culverts, bridges, and rural and urban drainage projects. The practical impact of an improvement in the precipitation data would be improved (more accurate) and reliable flood estimates for these projects.

1f What decisions are made by utilizing this data?

FERC: This data is used to make decisions concerning the safety and adequacy of existing or proposed spillways of jurisdictional dams.

USACE: Precipitation frequency data is used to access risk from USACE dams and for spillway design. It is also used in the design and analysis of new and existing flood risk reduction projects.

USBR: Risk-based dam safety decisions and designs, for Reclamation's dam safety program and other Department of Interior dams (BIA, NPS, FWS).

NRCS: Data are used to size auxiliary spillways and set top of dam elevations for small watershed dams constructed by NRCS. The data are also used to evaluate safety and adequacy of existing structures to determine rehabilitation designs. For flood hazard studies, NRCS uses data to estimate extents of inundation areas.

TVA: Use of PMP estimates to date has been driven by the need to show compliance with NRC and with TVA dam safety guidelines using a deterministic approach. Looking to the future, the development of extreme rainfall frequency data, and the use of improved hydrologic assessment capabilities will allow TVA to adopt a more rigorous approach to risk-informed analyses.

NRC: For proposed projects, the HMR data products are used to determine the suitability of specific sites and the design basis at those sites. The HMRs are used for design basis flood estimates as well as estimating design loads on structures due to both liquid and solid precipitation.

As part of the agency’s response to the Fukushima accident, US NRC has issued a “Request for Information” instructing all operating nuclear power plants to develop and report updated flood risk information for comparison against original licensing information. For sites where flood elevations and associated effects exceed the original licensing basis, licensees are expected to perform an integrated assessment to evaluate their flood protection and mitigation features and procedures Licensees’ evaluations use PMP values from the HMRs in some cases and in others, rely on site-specific PMPs. During the review period, licensees are actively engaging and revising protection and mitigation measures that depend in part on the HMR PMP estimates. The flooding reevaluations and integrated assessments will form the basis for regulatory decisions. The potential decisions range from changes in regulations regarding hazard assessment, protection and mitigation to modification of individual licenses.

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In the SDP process (described above), decisions include the assigning a significance/severity to identified deficiencies. Depending on the severity, orders to modify facilities can be issued and fines can be assessed.

USGS: See response to question 1.e.

2 Describe your agency views on the recommendations and priorities from “Estimating Bounds on Extreme Precipitation Events” NRC 1994 report (pp 19‐21), including: http://www.nap.edu/openbook.php?record_id=9195

NRC: The recommendations present probability-based standards as an alternative strategy particularly applicable to high-risk/high-complexity problems faced by U.S. NRC and other regulators. This strategy appears to have not advanced significantly since the 1994 report and obstacles are of key concern. The recommendations also focus on the need to find meaningful ways to apply PMP approaches to smaller geographic and shorter time scales. This should drive a focus on the “practices” of estimating intense rainfalls and the “processes” associated with reviewing the results. One obstacle that combines both probability based standards and practical applications is the paucity of practitioners for the work related to low probability/high events making the development and evaluation of technically defensible models a key constraint to this strategy. Advancements have clearly been made in the use of radar data, the extension of flood frequencies based on paleo-hydrology but the process of peer review needed for individual studies remains a key constraint.

The question regarding a national standard for consistency is complicated. There is a lack of consistency regarding both practices and peer review processes between Federal agencies, and it has created some problems. But the real question is consistency in what? And how would the consistency apply in light of differing risk tolerances? And could a standard be written without inhibiting innovation?

2a Continued use of PMP, or alternatives?

FERC: Continuously using PMP

USACE: Currently, the PMP is a design standard for USACE Dams. Alternative methods for developing PMP such as atmospheric modeling should be investigated, especially in the mountainous regions of the western U.S.

USBR: Reclamation uses alternatives to PMP, specifically including stochastic storm transposition and extreme precipitation frequency analysis.

NRCS: PMP will continue to be used as the design standard for NRCS dams.

TVA: The continued use of the development of Probable Maximum Precipitation is recommended. Advancements should be concentrated on a) ongoing maintenance of an extreme storms database, b) refinement of the mechanics of maximization and transposition, in

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keeping with the spirit of the HMRs, and c) estimating the probability of extreme rainfall events over watersheds.

NWS: NWS supports the continued use of PMP as an upper limit. We also recognize the need for risk based approaches relying on annual exceedance probabilities between the limits of NOAA Atlas 14 and PMP. And that methods for estimating those probabilities are not yet within the realm of common practice.

USGS: The USGS takes no official position on this issue, but notes that many experts in the field advocate a middle ground in which PMP methods may be available, but that efforts should be used to develop frequency-based estimates of extreme precipitation.

2b Use of Numerical models?

FERC: No

USACE: It would be beneficial if we could incorporate regional atmospheric models in the estimation of PMP, in addition to methods used to originally develop PMP index maps. Particularly along the West Coast, we could look at varying the angle of attack and sea surface temperatures from historical storms which could expand our knowledge of maximum precipitation potential.

USBR: Reclamation uses numerical models (WRF, MM5-class) for exploring science-based questions on extreme precipitation. We have been doing this on occasion since the early 1990s under the US GCRP (PMP sensitivity), and site-specific studies. Through several recent published studies (i.e. Green Mountain Dam), and ongoing research, we are committed to using this class of models to study and eventually estimate extremes. We are embarking on some ensemble-based case studies this year with NOAA-CIRES.

NRCS: Modeling in mountainous regions is problematic. While PMP issues are a part of that picture, one of the other major challenges is modeling snowmelt runoff and particularly rain on snow events.

TVA: Numerical models should continue to be researched as to their use in modeling extreme storm events, and once they are validated as accurate compared to empirical observation should be considered an option in extreme storm analysis.

NWS: NWS recognizes that the methods used in the HMRs are empirical with empirical extrapolations. Some of the assumptions have been shown to be questionable in certain circumstances. This leads to need to better understand the physics of the rainfall producing mechanisms in order to produce better estimates. We support investigation of physics based numerical models as a means for making better estimates.

USGS: The USGS generally limits its use of numerical models of rainfall and runoff processes to situations for which there is an adequate means of calibrating the model for the specific study basin and range of flow or precipitation.

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2c Assessment of radar accuracy?

FERC: No

USACE: Radar accuracy can be very poor to very good. Over the mountainous west, radar accuracy is poor. It can be very good over the eastern US particularly if the z-r relationships are calibrated to ground measurements. It is very beneficial for determining the spatial coverage of the storm. Radar accuracy has been improving and we should continue to use it over the eastern portion of the US

USBR: It is Reclamation's view that radar data (and more broadly gridded precipitation data) are essential to estimate extreme precipitation. We utilize multisensor estimates (MPE) in many studies. These blended products of gage (point) observations and radar reflectivity, with retrospective (reanalysis) processing with corrections (bias, bright band, AP, etc.) are essential. Recent work on accuracy and uncertainty estimates (done at Univ. of Iowa and Princeton) can really help in quantifying accurate estimates.

NRCS: Radar data is used within NRCS mainly as a way to evaluate effects of specific storm events. NRCS uses NEXRAD data as a major component of NRCS DamWatch software.

TVA: This is of particular interest to TVA, as ongoing reductions in our Operations and Maintenance budget effect the reality that fewer and fewer rainfall stations are maintained in the Valley. However, uncalibrated radar accuracy is a major problem in deriving rainfall accumulation and should not be used for analyses which are highly sensitive to these data. Private consultants and government agencies have been trying to improve the accuracy of radar data through post-analysis calibration of the information and this has shown to be reliable in determining rainfall accumulation.

NWS: Quantitative precipitation estimation (QPE) is fundamental to NWS operations. We have lots of experience, including multi-sensor precipitation estimation (MPE) which involves using other sensors to improve the quality of purely radar based QPE. There are several primary lessons learned from this experience:

i. The quality of radar based QPE without the use of other sensors is quite problematic. This also includes the use of model based land data assimilation systems.

ii. The effective coverage of NEXRAD radars is insufficient to provide full spatial coverage for QPE purposes, particularly in the west.

iii. Spatial resolution of the NEXRAD radars may not be sufficient to properly characterize PMP type events.

There are efforts under way to reconstruct rainfall estimates back in time, but they start to get problematic for years older than NEXRAD implementation.

USGS: The USGS takes no official position on this issue.

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2d Estimating probabilities of extreme rainfall? Currently no, however Commission is developing procedures to consider risk in dam safety analyses.

USACE: It is more important to estimate the probability of the flow or reservoir stage.

USBR: As previously noted, Reclamation estimates extreme rainfall probabilities using some of the techniques mentioned in this NRC report (e.g. ARR), as well as others (Hosking and Wallis, 1997). We require these estimates for dam safety risk analysis.

NRCS: Used within NRCS to evaluate effects of specific storm events

TVA: Absolutely. TVA is currently funding an effort to develop regional precipitation frequency relationships for several critical watersheds in the Tennessee Valley as a critical component to the ability to assign frequencies to extreme hydrologic events. Ongoing research to validate the utility of efforts to regionalize data is needed.

NWS: Research is needed. Methods for estimating those probabilities are not yet within the realm of common practice

USGS: The USGS sees the merit of developing probability-based estimates of extreme precipitation, but notes the required necessity of using short records relative to the rarity of the events for which estimates are sought.

2e Storm‐based analyses?

FERC: No

USACE: Publically available tools that do not rely on private software (ArcGIS) are needed to analyze historic storms. USACE is working on a tool called HEC-MetVue that will be extremely valuable in analyzing extreme storms.

USBR: Reclamation uses storm-based analyses based on older analyses, and conducts our own storm-based studies for individual watershed-scale studies. Newer storm-based studies are needed as well as studies that cover a wide geographic area to expand the data base. Reclamation's individual studies have limited coverage to transfer effectively to other sites.

NRCS Used within NRCS to estimate watershed scale project benefits and to evaluate effects of specific storm events

TVA: The availability of adequate storm-based data is perhaps the key element in conducting extreme rainfall analysis.

NWS: Storm based analysis is fundamental to understanding the physics of rare rainfall producing mechanisms. It’s therefor necessary to improving upon the methods used in the current HMRs.

USGS: The USGS takes no position on this issue.

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2f Is there a need for a national standard for consistency?

FERC: Yes

USACE: Yes, but methods may need to vary by geographic location

USBR: Yes, national standards are needed on extreme storm methodologies and basic data.

NRCS: Yes. Having a national standard, particularly for site-specific PMP would be beneficial. NRCS needs confidence in PMP data and methods.

TVA: Yes. TVA’s efforts to interpret the guidance in the various relevant HMRs have led to the conclusion that a clear national standard would be helpful to the hydrologic engineering community. TVA believes the development of a national standard should include efforts by all who have made valid contributions to the study of extreme rainfall, and not be limited to any one sector. TVA also believes that a national standard must recognize that variations in topography and meteorology cause large regional variations in extreme storm dynamics.

NWS: Yes, without a trusted national standard, users will be tempted to make independent estimates of PMP, and these may vary quite a bit in quality. Consistency is necessary to equitable funding among projects.

USGS: Yes. General guidelines are needed to drive application of analyst’s judgment and permit the comparability of estimates from different sources.

3 Discuss your thoughts and views on the priorities – risk analysis, standards, and meteorology, from the “Hydrologic Research Needs for Dam Safety” FEMA workshop, USACE 2001 report (pp. 171‐176) (also later published by FEMA in 2005), including these three from the top 10: http://www.hec.usace.army.mil/publications/SeminarProceedings/SP‐29.pdf

NRC: Generally all three areas are important, however, a fourth area associated with U.S. NRC needs for extreme rainfall data is development of appropriate peer review processes to handling all three areas. This is relevant to needs at individual sites whether they be dams, flood prone sites, existing nuclear power plants, etc. It should be noted that considerable advancement has occurred related to both paleo-hydrology and use of NEX-RAD data since that report was prepared.

It should also be noted that there are differences in risk tolerances for nuclear facilities compared to dams, so that U.S. NRC has a somewhat different perspective on some of the priorities: 1) U.S. NRC is interested in hazard curves that extend significantly beyond the 1 in 10,000 year ARI; 2) simply extrapolating frequencies does not seem appropriate since this ignores potentially significant epistemic uncertainties

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Also, for U.S. NRC’s needs associated with high-risk/high-complexity issues, and the trend towards PFHA, greater focus on the peer review associated with these advancements is critical. The document’s focus on risk analysis, rather than risk-informed decision making oversimplifies the challenges that U.S. NRC, and presumably other agencies, face.

3a Historical database of storms and floods?

FERC: Yes, but not for every project. FERC uses available publications issued by the NWS or any other credible supporting information published by other entities.

USACE: The USACE Extreme Storm Team is in the process of developing a storm database. When this is completed, a tool will be necessary to extract information from this database and apply it to a hydrologic model. Our current plan is to link the HEC-MetVue tool with the database and the HEC-HMS model.

USBR: This is still priority 1, and needs to be completed. The historical storms should be digitized and made available in an electronic format. More current storm analyses also need to be included. We are performing individual storm studies for this effort, but do not yet have a repository. USACE is making progress on a larger data base, and has a prototype. We will be sharing data with USACE and anticipate using their data base.

NRCS: NRCS relies upon other federal agencies for precipitation estimates and extreme storm event data; and could make good use of such data and tools were they available to us.

TVA: There is no substitute for good observational data of historic storms and floods. A historical database should be continually updated and made available to all in the engineering community.

NWS: A historical database is necessary to the storm based analysis mentioned above

USGS: The database on which the extreme precipitation estimates are based should be updated to include more recent storms. In particular, the database should include the storms for which estimates of aerial distributions and intensities can be developed using Doppler radar and other remotely sensed sources, as well as, point or gaged estimates

3b Precipitation Analysis needs?

FERC: Yes

USACE: The Corps is developing a GIS based meteorological software tool (HEC-Methuen) that can be used to catalog historic storms and apply the storms to a geographical area to create different alternatives (what-if scenarios). HEC-Methuen will be linked to HEC-HMS to develop flow estimates for the precipitation events.

USBR: This is an important priority and work needs to be done in this area. If precipitation analysis and hydrometeorology is done on a finer regional scale, and cover the entire nation, it could help refine critical storm types, durations, spatial scales, define homogeneous regions, and transposition zones and probabilities.

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NRCS: NRCS relies upon other federal agencies for precipitation estimates and extreme storm event data; and could make good use of such data and tools were they available to us.

TVA: The systematic analysis of major storms should be preserved, and continually built upon. Much work has been done in this area over the last couple of decades by private consultants, and TVA believes this has resulted in a contribution to the profession that should be recognized by the entire community.

NWS: Storm based analysis mentioned above includes precipitation analysis.

USGS: The USGS has no position on the topic.

3c Extend frequencies?

FERC: Yes

USACE: The USACE has a draft document for extending frequency curves out to the PMF event. Currently under development are software tools that will provide the ability to follow recommendations in the draft document.

USBR: We have methods to do this, and are happy to share them. More efforts are certainly needed.

NRCS: NRCS relies upon other federal agencies for precipitation estimates and extreme storm event data; and could make good use of such data and tools were they available to us.

TVA: TVA believes this is a critical element to establishing probabilities of, and reducing the uncertainty associated with, flood discharges and elevations for extreme events, and should be a high priority for ongoing research and development.

NWS: As mentioned above, NWS recognizes the need for risk-based approaches relying on annual exceedance probabilities between the limits of NOAA Atlas 14 and PMP. And that methods for estimating those probabilities are not yet within the realm of common practice.

USGS: The USGS has no position on the topic.

4 Describe what your agency would like to incorporate and support that came out of the Probabilistic Flood Hazard Workshop held at the Nuclear Regulatory Commission in January 2013 http://www.nrc.gov/reading-rm/doc-collections/nuregs/conference/cp0302/ (pp. 10-4 to 10-7)

NRC: The list that follows seems limited. Development of a more global framework (similar to the framework used for other hazards such as seismic) for specific flood hazards (in this case PMP) that can be used more consistently should be pursued.

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NWS: The PFHA provided broad coverage of potential state of the art approaches. Most all of them should be further examined as part of the research necessary to improve the science.

USGS: The USGS would endeavor to support these activities through participation in any advisory or oversight committee that ACWI wishes to form. In particular, the USGS could offer some expertise in the regionalization and stochastic modeling process but any such support would either be limited in scope or duration or require funding assistance.

4a Focus on extreme rainfall observations and improve databases

FERC: Yes

USACE: The USACE extreme storm team is developing a database of historic extreme storms. This will provide a common database for all agencies to share extreme storm data. Long term plans need to be developed to determine which agency maintains and updates the database once it is complete.

USBR: We can contribute our existing data to this, and other ongoing data analyses.

NRCS: NRCS relies upon other federal agencies for precipitation estimates and extreme storm event data; and could make good use of such data were they available to us.

NRC: This is necessary but not sufficient. The database of extreme storms will always be sparse and in need of supplemental approaches. Simply updating the storm catalogue and applying 40-year old methods does not seem like a technically defensible approach.

4b Explore advances in data-processing methods

FERC: Yes

USACE: Currently, USACE is using Arc-GIS along with other tools to analyze and process historical storm information. We are also developing a tool called HEC-MetVue to streamline the data processing.

USBR: We can share our current methodologies, and collaborate on efforts using numerical models. Our focus is on gridded precipitation data at a fine resolution.

NRCS: NRCS relies upon other federal agencies for precipitation estimates and extreme storm event data; and could make good use of such data were they available to us.

NRC: We don’t know what this means.

4c Develop regionalized techniques

FERC: Yes

USACE: The USACE Hydrologic Engineering Center (HEC) is in the process of adding a regional frequency analysis tool to HEC-SSP.

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USBR: We are happy to share techniques we are using and discuss ways to improve them.

NRCS: NRCS relies upon other federal agencies for precipitation estimates and extreme storm event data; and could make good use of such data were they available to us.

NRC: Regionalized approaches for estimating precipitation frequency exist and are commonly used, although not for “PMP-scale” precipitation. It seems reasonable that regionalization would play some role in estimating magnitude and frequency for extreme precipitation.

4d Stochastic methods

FERC: Yes

USACE: HEC is also adding Monte Carlo simulation capabilities to sample meteorologic, hydrologic, and reservoir operation parameters. These tools can be used to extend flow and reservoir stage frequency curves out to the PMF event.

USBR: We are also happy to share techniques we are using and ways to improve them.

NRCS: NRCS relies upon other federal agencies for precipitation estimates and extreme storm event data; and could make good use of such data were they available to us.

TVA: TVA is certainly not philosophically opposed to any of the above research areas. In a world characterized by shrinking budgets, it is critical that funding to support the development of these and perhaps other techniques be justified by reasonable expectations of cost savings and efficiencies. Sharing “success stories” associated with the application of these methodologies may benefit the entire community.

NRC: Stochastic methods (both event-based and continuous modeling) should be pursued. In order to apply a more risk-informed regulatory approach to flooding (an agency priority) better estimation of the probabilities associated with extreme events is needed.

However, a risk-informed regulatory approach also requires the development of processes to rigorously evaluate controversial and ambiguous information associated with both data and methodologies. The need to address uncertainty regarding the interpretation and use of such data is equal to the uncertainty of the data itself.

Right now, it seems like probabilistic evaluations are performed in rather ad hoc ways. It also seems that different individuals are doing PFHA rather differently and there’s not much focus on developing an overall framework. This doesn’t seem like an appropriate approach to developing a broadly accepted methodology that reflects the collective community of knowledge.

5 Discuss applicability of current Federal extreme precipitation publications, databases and tools:

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5a HydroMeteorological Reports (HMR)

5a.i What information do you glean from the HMRs? And how do you use this information exactly?

FERC: PMP values. Following FERC Engineering Guidelines, PMF Determinations use the PMP value for hydrologic modeling to determine the PMF value.

USACE: Within USACE, the HMR reports are used to develop the PMP storm. We follow the procedures outlined in the HMR to develop the PMP storm in 1 to 6 hour time increments. The storm data are used with a hydrologic model to develop the PMF hydrograph.

USBR: We use PMP estimates, DAD tables and ancillary storm data used in the PMP estimates, depth-area curves, area reduction factors, and snowpack information (where available). Focus is usually on general storms. We utilize the individual storm analyses (and DAD tables) used in estimating PMP for historic storm spatial and temporal patterns for scaling up from basin-average precipitation frequency relationships.

NRCS: PMP values.

TVA: Rainfall data and techniques on how to develop and apply PMP rainfall over basin sizes ranging from point (1 mi2) to large (over 25,000 mi2) watersheds. Rainfall data thus derived are used to drive hydrologic and hydraulic simulation models to determine PMF levels at critical locations.

NRC: PMP values and guidance. PMP values at watershed scale are used to develop PMF estimates. 10-square mile PMP values are used with HMR 52 to estimate local intense precipitation.

The 48-hour probable maximum winter precipitation (PMWP) is used for design ice and snow loads on structures.

USGS: The response to question 1B.

5a.ii Which information is most useful?

FERC: General/local PMP values

USACE: The PMP Index maps, DAD tables, temporal distribution, examples

USBR: The individual storms that are the basis of PMP

NRCS: Estimates of PMP

TVA: Rainfall depths and application guidance.

NRC: PMP values and HMR52 guidance.

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USGS: Site-specific and watershed estimates of the depth-duration-frequency estimates. The most commonly used duration is 24 hours, but the frequency interval ranges typically are from 2–100 year events.

5a.iii Do you use the spatial and temporal storm patterns provided?

FERC: Yes

USACE: Yes for PMP, Sometimes the spatial patterns are also used for frequency based storms for large watersheds.

USBR: Yes, typically for screening-level studies and comparisons. For more detailed studies, we derive these relationships.

NRCS: Typically for NRCS small watersheds, point values are used. Temporal storm patterns are evaluated, but NRCS criteria provides guidance on temporal distributions used within NRCS.

TVA: Yes

NRC: Yes

USGS: Only to estimate watershed specific precipitation estimates per the response to questions 5A-ii.

5a.iv Do you use the Depth-Area-Duration (DAD) tables?

FERC: Yes

USACE: Yes, we also use them for developing depth-area reduction factors for frequency based storms for large watersheds.

USBR: Yes

NRCS: Yes

TVA: Yes

NRC: No

USGS: No

5a.v Do you use the HMRs to compute PMP?

FERC: Yes

USACE: YES, unless we do a site-specific PMP study.

USBR: Yes, in most situations.

NRCS: Yes. Unless more current special studies are available.

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TVA: Yes

NRC: Yes

USGS: No

5a.vi Do you use the HMRs to compute a percentage of PMP? Which percentage?

FERC: No

USACE: Yes, in the western US we use 50% of PMP to represent the Standard Project Storm.

USBR: We do not use PMP percentages.

NRCS: Yes. Most often when evaluating state-specific criteria compared with NRCS criteria for freeboard design storms. (Generally 0.5PMP or 0.75 PMP).

TVA: No

NRC: No

USGS: No, N/A.

5a.vii Do you use the areal reduction factors provided in the HMRs?

FERC: Yes

USACE: Yes

USBR: Yes. For detailed studies, we usually derive a site-specific relationship.

NRCS: Yes.

TVA: Yes.

NRC: Yes.

USGS: No.

5a.viii Do you consider storm seasonality in your studies?

FERC: Yes

USACE: Yes, for some areas that may have a combination of snowmelt and rainfall for the probable maximum flood.

USBR: Yes. This factor is critical in the western US.

NRCS: Yes. Mainly in areas where snowmelt and rain on snow are factors.

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TVA: Yes - primarily due to the variation in seasonal flood storage allocation at TVA reservoirs.

NRC: Yes.

USGS: No.

5a.ix Which HMR do you consult the most often?

FERC: HMR 51/52 and HMR 58/59

USACE: HMR51/52 since 80 percent of USACE dams are located in this region.

USBR: We use HMR 49, 55A, 57 and 59 equally in the western US, and HMR 51 to a lesser extent.

NRCS: HMR 51 and 52. Most NRCS dams are located in this region. However, all are used.

TVA: 41 and 56.

NRC: We rely most heavily on PMP values in HMR 51 and HMR 52 guidance which cover regions applicable to the majority of the sites US NRC regulates. Other HMRs are used for sites outside of the HMR51 regional coverage.

For snow and ice loads on structures, our Standard Review Plan references HMR 49, 53, 55A, 57 and 59.

USGS: Atlas 14.

5a.x Are the HMRs easy to use? If not, why?

FERC Yes, except snowmelt estimations.

USACE: No, they are all slightly different in application. We are developing tools to perform the calculations to simplify. Currently we have a tool for HMR51/52 and HMR57.

USBR: No. The lack of gridded, electronic versions of the plates, maps, etc. impedes efforts to import the plates, maps, etc. into a GIS environment. The challenges with portions of HMR 49 are somewhat involved.

NRCS: No. Procedures vary somewhat region to region.

TVA: No. TVA’s experience is that the HMRs contain little information on how data were analyzed and used, and the available guidance is such that replication of results from one analyst to another is problematic.

NRC: Yes though HMR52 is less so.

USGS: Yes.

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5a.xi Do you use the digitized HMR 51 plates? Or the shapefiles available for HMR 58 and 59?

FERC: Yes

USACE: We use the HMR 58/59 shapefiles. It would have been helpful to have the shapefiles for all of the figures in HMR 59 available (and not just the index PMP). However, we have had success in digitizing the figures that we do need that aren’t available.

USBR: Yes we use both.

NRCS: Yes.

TVA: No.

NRC: No.

USGS: No.

5a.xii What would you change about the HMRs when/if updated?

FERC: Updating PMP value, clarifying snowmelt procedures, additional work and methods to address orographic effects, etc.

USACE: Have an automated tool to work with each HMR.

USBR: Complete numerical database to reproduce results. All gridded information, on a much finer scale than the generalized estimates. Full uncertainty, and estimates of exceedance probabilities blending with full precipitation frequency curves. Enhanced spatial patterns for orographic regions.

NRCS: Update PMP values. Expand database. Make HMR shapefiles available for the entire nation.

TVA: Carefully review and include all relevant work done since the HMRs were published, whether done in the public or private sector, incorporating advancements and updated storm data bases. Ensure the updated HMRs are clearly written, produced in coordination with the user community, and make available all background data/information/materials for verification and understanding of results.

NRC: Address “stippled areas” in HMR 51

Address area limitations

• Large watersheds (e.g., Missouri, Mississippi rivers) • Bridge gap between point estimates and existing 10-sqaure mile estimates

Provide precipitation estimates that are more suitable for design snow and ice load calculations in relevant regions (i.e. cool season, or winter months; 48-hour durations)

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NWS: We’d like, as much as possible, to see standard tools or “services” that automate the procedures in the HMRs

USGS: The USGS has specific suggestions to offer.

5a.xiii What additional information would you want to see included?

FERC: Remove subjectivity that is in most of the HMR’s.

USACE: We should look at atmospheric modeling particularly along the western US for aiding development of PMP estimates.

USBR: See previous answer.

NRCS: Automated procedures

TVA: More consistent guidance on a) the development of antecedent and subsequent rainfall amounts, including a discussion of resulting combined probabilities, and b) the existence and location of the zero rainfall isohyet.

NRC: An online digital product similar to the NOAA Atlas 14 Precipitation Frequency Data Server. Probabilities and confidence intervals associate with estimates

USGS: The USGS has specific suggestions to offer.

5a.xiv Do you use any other studies besides the HMRs for PMP?

FERC: Yes, site specific PMP studies, particularly in the stippled regions.

USACE: Yes, site specific PMP studies.

USBR: Yes, we use Reclamation's design storm studies for individual dams (if available, as these past studies were used for design (in most cases), rather than PMP. These estimates are used for comparisons.

NRCS: Special studies for site-specific PMP as available. Regional PMP studies developed by others if available and generally accepted by state dam safety agencies.

TVA: No.

NRC: We are currently faced with reviewing site-specific PMPs developed by licensees (i.e., by their consultants).

USGS: N/A.

5a.xv Do you estimate PMP probabilities? If so, how?

FERC: Currently, no.

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USACE: No, but we do estimate probabilities of the PMF using several different methods including 1) extrapolation of volume probability curve, 2) rainfall runoff modeling to the 1000 yr event to guide extrapolation, 3) regional precipitation method, 4) GRADEX method, 5) Stochastic Extreme Flood Modeling.

USBR: Yes, using ARR, regional precipitation frequency analysis for the dam and region of interest, and stochastic storm transposition (in a few cases).

NRCS: No.

TVA: TVA does not currently attempt to define PMP probabilities.

NRC: No but we occasionally have licensee’s attempt doing this without established guidance or methodologies.

USGS: No.

5b NOAA Atlas 14

NWS: As the producer of NOAA Atlas 14, we’re looking forward to user comments here.

5b.i NOAA Atlas 14 is being updated to include the Northeastern states (from TP40). Funding has not yet been found to update estimates for Texas (from TP40) or the Northwestern states (from NOAA Atlas 2). How important is it to your organization to have NOAA Atlas 14 volumes for Texas and the Northwestern states?

FERC: NOAA Atlas 14 is important to FERC, especially to those projects in the northwestern part of US to help determine reasonableness of a PMP or site-specific PMP estimate. Frequency estimates are compared to PMP/PMF determinations to determine reasonableness of computed values.

USACE: It is extremely important that NOAA update frequency precipitation for remaining areas. Otherwise, engineers will continue to use outdated information. The NWS is a better alternative to private consultants and other state/local agencies for performing frequency precipitation updates due to experience, practice in other regions, and independence from the application of the updated frequency precipitation data.

USBR: It is important to have NOAA 14 for the Northwestern states, as we have many facilities in that region. We are less interested in Texas, because there are very few DOI facilities in that state.

NRCS: NRCS uses Precipitation-frequency data for design of engineering based conservation practices as well as dam designs. In those areas where NOAA Atlas 14 is updated, we are using those values. In areas where NOAA Atlas 14 is not updated, we still rely upon the old TP-40 data, NOAA Atlas 2 data or data developed by others than NWS, if available.

TVA: Not important to TVA as these areas lie outside the Tennessee River watershed.

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NRC: This would be of low to medium importance for US NRC (but could change based on what applications are submitted). There are a number of licensed facilities operating in Texas and Northwestern states. However, for the applications of interest for operating large commercial U.S. nuclear reactors, the ranges of precipitation needed may be outside those justified for extrapolation by NOAA and other entities. Hence, while the information can be useful up to 1000 years to justify that less intense, more frequent precipitation events not impact a site severely, most ranges of interest may exceed 1000 years and, therefore, may need additional methodologies/data for full use in risk assessment. However, US NRC would be very interested in the result of additional NOAA Atlas 14 studies.

USGS: The USGS has conducted an extensive Texas-specific analysis of depth-duration frequency with data through 1994. The results are published in two USGS Scientific Investigations Reports. The USGS is trying to fund a study into coefficients by county in Texas to implement intensity-duration estimation into framework used by Texas Department of Transportation (TxDOT). Other agencies or investigators have periodically looked at more modern time periods and have found agreement with existing depth-duration frequency. Whereas, the USGS cannot speak directly for TxDOT, it seems a lack of interest exists for funding further statistical studies of precipitation.

5b.ii What information do you glean from NOAA Atlases 2 and 14? And how do you use this information exactly?

FERC: 100-year precipitation from both NOAA Atlases 2/14; 100-yr and 1000-year values from NOAA Atlas 14. The ratio of the NOAA 14 to NOAA 2 (100-yr, 24 hr) values can be considered as an important index to update HMR-59 PMP estimates.

USACE: Typically, USACE studies obtain the depth-duration frequency precipitation data and develop hypothetical design storms (generally less than 400 square miles). If the storm is greater than 400 square miles then area reduction is a big concern and depth area reduction factors are based on historical storms or from the HMR’s. The NWS depth area reduction factor study currently under way will be valuable for us.

USBR: We use the published point precipitation frequency (1/50, 1/100, 1/1000 if available) for each site, and use ARR or other methods to extrapolate. We also extensively use the time series data behind NOAA 14 to conduct site-specific or regionalized precipitation frequency for an individual dam or project.

NRCS: Point values for 1- to 100-year return intervals. Used as design storms for hydrologic sizing of engineering based conservation practices

TVA: Occasional reference to NOAA Atlas 14 is made to estimate the probability of observed rainfall events.

In addition, TVA’s PMP consultant uses data from NOAA Atlas 14 as part of the site-specific PMP study to help define the effects of topography on rainfall and in defining transposition limits. In addition, the PMP values are compared to the NOAA Atlas 14 values as one of several comparisons to help define reasonableness of PMP values.

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NRC: As mentioned above, for risk assessment purposes, NOAA Atlas 14 data may provide an initial assessment of the potential impact of precipitation on an area surrounding a licensed facility, such as a nuclear reactor. The information would not be used as a final answer for decision-making since most ranges of interest for flooding events impacting nuclear reactors exceed 1,000 years, but may be used in a risk-informed manner. If an issue is identified where NOAA Atlas 14 may indicate an area of additional regulatory oversight is warranted, this information would be used to then couple any precipitation impact with an evaluation of plant response in an integrated system/human probabilistic risk assessment model for follow-up regulatory activities.

USGS: See response to question 1b.

5b.iii Which return period is most useful to your studies?

FERC: 100-yr for a low hazard dam; 1000-yr for a high/significant dams.

USACE: Typically we look at full range of frequency storms from 2-yr to 500-yr or 1000-yr.

USBR: We focus on a full distribution, rather than individual return periods. AEPs of most interest are 10-3 to 10-6.

NRCS: Point values for 1- to 100-year return intervals.

TVA: 100- and 500- year frequencies are most important because of their relevance to floodplain management.

NRC: The full hazard curve, usually in excess of 1000 years (up to and beyond 1,000,000 years) is of interest.

USGS: 2-100 year.

5b.iv Do you extrapolate beyond the 1,000‐year return period (not recommended by NWS)? If so, how?

FERC: No

USACE: Extrapolation beyond the 1000yr might be necessary when running Stochastic models simulations to define flow and stage frequency curves out to the PMF event.

USBR: Yes. See presentations at the NRC PFHA workshop, Reclamation's Hydrologic Hazard Guidelines, and previous answers. Our current preferred way is basin-average regional precipitation frequency.

NRCS: No.

TVA: No.

NRC: In a limited basis and as a risk-informed exercise to evaluate information submitted to the NRC, since multiple licensees have performed such extrapolations on NOAA

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Atlas 14 and other hydrologic databases, as a way to respond to NRC regulatory activities. In this sense, the NRC is not necessarily interested in pursuing these limited credibility extrapolations, but rather responding to requests to consider risk insights based on submitted information. The NRC is aware of the limited technical justification for doing so and therefore uses significant caution in these cases.

USGS: USGS does not extrapolate precipitation estimates.

5b.v Which duration(s) is most useful to your studies? 6/24/72-hour durations.

USACE: All durations are necessary, shorter duration drive the peak flow for smaller watersheds and longer durations are important for volume.

USBR: Typically general storms (48 hrs to 72 hours); we also examine storm sequences over longer (12 day) periods. In some cases, thunderstorms (<6 hours) are of interest. Duration is highly dependent upon the conditions specific to the watershed.

NRCS: 6-hour and 24-hour

TVA: N/A.

NRC: All durations (short, long) are of interest.

USGS: 24-hour.

5b.vi How do you determine your storm duration(s)?

FERC: 72-hr for general storm or 6-hr for local storms.

USACE: Storm durations are typically determined by evaluating the critical duration of the study area (time of concentration, reservoir characteristics, downstream operation).

USBR: Analysis of historical extreme storms, and integrate watershed and reservoir characteristics.

NRCS: NRCS criteria specifies use of 24-hour durations for most conservation engineering based practices (typically designed on the 10-year to 50-year return interval). NRCS criteria for dam designs specifies use of 6-hour and 24-hour durations in evaluation of auxiliary spillways. However, NRCS criteria for dam designs also requires checking of other durations to assure that the critical storm duration is used for design.

TVA: N/A.

NRC: For new facility license applications use:

1) time of concentration for watershed; 2) analysis of historical events. For operating facilities usually evaluated against an existing design bases or other flooding scenario.

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USGS: USGS primary hydrologic computations involving storm duration are associated with concepts such as the characteristic time of a watershed for modeling purpose. The USGS does not engage in site-specific design computations so seldom is a need to use administratively incorporated storm durations in "design manuals."

5b.vii NOAA Atlases 2 and 14 contain point‐based precipitation. Do you need areal information?

FERC: Yes

USACE: Yes, area reduction information is necessary.

USBR: Yes, areal estimates are required for most of our projects.

NRCS: Occasionally. NRCS includes guidance on making areal adjustments (based on old TP-40 recommendations).

TVA: Yes.

NRC: Yes, areal information has become an issue of discussion in recent regulatory activities.

USGS: Yes, for specific watersheds.

5b.viii Do you currently compute areal estimates based on the point values from NOAA Atlas 2 or 14? If so, how? And where/how do you obtain your areal reduction factors if you use that method?

USACE: Yes, for watersheds less than 400 sq mi area reduction comes from TP40. For larger watersheds we use area-reduction information from historic storms or as contained in the HMR documents.

USBR: Yes, we compute areal estimates. We use ARFs from other NOAA published reports, HMRs, USDA-ARS research watersheds (e.g. Walnut Gulch, Reynolds Creek), and site-specific estimates we prepare for individual studies. Storm data, DAD tables, analysis of new storms, and transposed storms are used in making basin-average precipitation estimates. Some details were presented at the NRC PFHA workshop.

NRCS: Currently based on old TP-40 recommendations.

TVA: No.

NRC: Licensees have submitted areal estimates on point values from NOAA Atlas 14 and the NRC had to evaluate the implications of this information for reactor oversight purposes. ARF guidance from NOAA Atlas 14, NOAA Atlas 2, NOAA TP-40, state and federal drainage manuals, as well as various studies reported in literature.

USGS: Use the plates in and interpolate to center of watershed or rely on USGS publications on areal reduction factors.

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5b.ix Which region of the United States is of most interest to you for precipitation frequency estimates?

FERC: Entire country

USACE: We have projects in all regions of the US so all areas are important. The highest priority now would be the areas not covered by NOAA14, the northwest, northeast and Texas.

USBR: The 17 western states are of most interest. Other states (coterminous) are of secondary interest, and are needed for assessing DOI facilities.

NRCS: All.

TVA: The southeast.

NRC: The NRC licenses and regulates licensees throughout the U.S., hence, all regions are of interest. However, current nuclear facilities, such as large commercial nuclear reactors, are concentrated on the East Coast, South, Northeast, and West Coast.

USGS: All regionals are equally important now, but going forward those regionals near coasts and subject to hurricanes will likely gain in importance.

5b.x Did you use NOAA Atlas 2 or TP40 before NOAA Atlas 14 volumes were published?

FERC: Yes for 100-yr precipitation

USACE: Yes, we used both NOAA 2 and TP40, also HYDRO-35 for short duration storms.

USBR: Yes, extensively. NOAA Atlas 2 provides the base spatial pattern in HMRs 57 and 59, and was useful for isopercentile analysis.

NRCS: Yes.

TVA: Yes.

NRC: Used TP40 before NOAA Atlas 14 was available.

USGS: Yes.

5b.xi Do you still use NOAA Atlas 2 or TP40? Where for? And for what purpose?

FERC: Yes, for the areas not covered by NOAA Atlas 14 for dam safety analyses.

USACE: We still used NOAA 2 for the northwest, TP40 for the northeast and Texas

USBR: Yes. We use Atlas 2 and TP-40 on occasion for point frequency estimates at sites not covered by NOAA 14. Estimates are made and extrapolated (usually with ARR) for dam safety screening-level studies.

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NRCS: NOAA Atlas 2 still used for the Northwest (those states not yet updated). TP-40 still used for Texas (not yet updated). For design of engineering based conservation practices and for dam design.

TVA: No.

NRC: No.

USGS: No.

5b.xii To what extent is NOAA Atlas 14 information incorporated into design guidance or regulations that govern what you do?

FERC: 100-yr storm

USACE: We typically use the most recent precipitation frequency information from NOAA.

USBR: Reclamation design guidance is flexible and not prescriptive. We mention NOAA 14 as useful and show examples in our Hydrologic Hazard Guidelines for dam safety.

NRCS: NRCS engineering policy requires use of available existing hydrometeorological data for planning, design, and operation of water-related structures and systems; and provides a prioritized list of data sources. In policy, that list is as follows:

(1) NRCS National Water and Climate Center (NWCC).

(2) U.S. Geological Survey (USGS).

(3) National Oceanic and Atmospheric Administration (NOAA).

(i) National Weather Service (NWS).

(ii) National Climatic Data Center (NCDC).

(4) Regional climate centers (RCCs).

(5) State climatologists.

(6) USDA sister agencies.

(i) Agricultural Research Service

(ii) Forest Service

(7) Other Federal, State, and local agencies having planning responsibilities for water-related projects, operational responsibilities, or both.

NRCS dam design criteria (TR-60) specifies use of NWS data unless special studies are used.

TVA: N/A.

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NRC: It is not. Limited information has been used for oversight of current operating nuclear reactors. NOAA Atlas 14 was not available during original licensing in almost all cases.

USGS: N/A.

5b.xiii Are there elements in NOAA Atlas 2 or TP 40 missing in NOAA Atlas 14?

FERC: Unknown

USBR: Nothing of major substance.

NRCS: Unknown

TVA: Areal adjustment factors.

NRC: Don’t know.

USGS: No.

5b.xiv Is NOAA Atlas 14 easy to use? How could it be improved?

FERC: Yes

USBR: It is very easy to use. Improvements could be made to include realistic, storm-based temporal and spatial patterns, and extrapolation to AEPs of interest. Distribution choices could be refined for specific durations. The inclusion of distribution uncertainty would be an improvement, as extrapolation estimates are largely a function of distribution choice.

NRCS: NRCS uses NOAA Atlas 14 downloaded data to derive temporal rainfall distributions for the 1- through 100-year return intervals. Maintaining a consistent format for that downloaded data would be extremely beneficial.

TVA: Yes.

NRC: Availability and flexibility of using original data, including publication of parameters for fitted extrapolations would be useful.

5b.xv Do you input latitude/longitude values into the web interface?

USACE: Yes

USBR: Yes, on occasion.

NRCS: Yes.

TVA: Rarely.

NRC: Sometimes.

USGS: Yes.

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5b.xvi Do you consult the isopluvial maps of precipitation frequency estimates for a particular exceedance probability and duration? If so, what value do they provide beyond the GIS compatible grids of the same information?

FERC: Yes. The maps can provide quick rough estimates.

USACE: Yes, sometimes they are simpler to use for quick estimates.

USBR: We use the GIS grids. The maps are not very helpful, other than to have a quick look at a regional pattern or some drainage.

NRCS: Occasionally.

TVA: No.

NRC: No.

USGS: No.

5b.xvii Of what value are the temporal distribution curves in NOAA Atlas 14?

FERC: Unknown

USACE: This area needs to be improved. The temporal distributions are not valuable because they wash out the intensity of actual rainfall events. Averaging a number of precipitation events together to get a generalized pattern results in lower intensities. Instead, time-patterns from historic events would be more useful.

USBR: They are a somewhat useful starting point for temporal patterns. We typically rely on individual gages or patterns from an individual extreme storm (or ensemble of storms).

NRCS: NRCS procedures were developed for deriving temporal distributions from the rainfall values. These procedures differ from the procedures used by NWS to develop temporal distributions. We do not typically use the temporal distribution curves in NOAA Atlas 14.

TVA: N/A.

NRC: They are of value in terms of comparing different contributors from a combined risk perspective (i.e., as opposed to evaluating a single extreme storm of very low exceedance probability).

USGS: N/A.

5b.xviii Of what value are the seasonal curves in NOAA Atlas 14?

FERC: Unknown

USACE: They are useful for rain on snow events.

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USBR: They are somewhat helpful for a starting point to examine the maximum extreme storm/flood season. We don't use them in much detail.

NRCS: We not use them. They may be helpful for evaluating rain on snow events.

TVA: N/A.

NRC: They are of value, since many licensees have submitted information assessing the probability of flooding impacts based on seasonal information arguments. Having this information available in advance is greatly beneficial.

USGS: N/A.

5b.xix There is a difference between precipitation frequency estimates more frequency than about 15‐20 years ARI for estimates derived from annual maximum series and estimates derived from annual maximum series and estimates derived from partial duration series. How important is it for NOAA Atlas 14 to provide both? Which of the two is your preference and why?

FERC: It is important to provide both for which the conservative one is chosen.

USACE: We typically do not use the partial duration series unless we are computing agricultural flood damages.

USBR: Given PDS and AMS estimates typically converge at about 1/20 AEP, and our estimates are 10-3 to 10-6, we prefer AMS for tradition and simplicity. Site-specific and custom studies can alleviate any potential issues, if there is a cluster of extreme storms within a year.

NRCS: In general partial duration series estimates are more valuable to us for design of engineering based conservation practices because these designs rely upon the 10- to 50-year return interval events.

TVA: Important. 100- and 500- year frequencies are most important because of their relevance to floodplain management.

NRC: NOAA should provide both estimates for short ARIs. For short ARI’s, PDS would provide more complete risk information (i.e., the threshold set in the PDS could be set with the facility fragility in mind).

USGS: Use of partial duration series analysis remains in the realm of individual investigation circumstances.

5b.xx Do you consult the report documentation of NOAA Atlas 14 for any purpose?

FERC: Yes, for 100-yr storm and procedures.

USACE: Yes – It is important to understand the data used and methodology for developing index precipitation maps

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USBR: Absolutely; the documentation is invaluable and required in order to extrapolate any of the regional distributions.

NRCS: Yes. It is important to understand how the data was developed in order to use it properly.

TVA: No.

NRC: Occasionally. For the basis on the extrapolated precipitation curves in the NOAA Atlas 14 interface website

USGS: Yes, it provides background needed to select specific frequencies.

5b.xxi Do you use any of the background information that the NWS used to compute the precipitation frequency estimates? If so, what exactly? (e.g., gauge data, clusters)

FERC: No

USACE: We use extreme storm data in site specific PMP studies and will be using it to update our Standard Project Storm criteria.

USBR: We extensively use the gage data that are the basis for the estimates. We also use the regions, for those studies that relied on geographically-fixed regions (as opposed to the newer ROI estimates).

NRCS: Yes. The background information, particularly gage data, is important for us in calibrating models.

TVA: No.

NRC: No.

USGS: N/A.

5c National Storm Catalog (USACE big black book of storms)

5c.i Do you have a copy of this book?

FERC: No

USACE: Yes

USBR: Yes. Hard copy and electronic (pdf) versions.

NRCS: No.

TVA: No.

NRC: Yes, but seldom consulted.

USGS: No.

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5c.ii What information from this book do you use?

FERC: N/A

USACE: Primarily the Depth Area Duration tables.

USBR: DAD tables, storm orientation, maximization factors, etc.

TVA: N/A.

NRC: Not really used.

USGS: N/A.

5c.iii If the book was digitized, would you use the information?

FERC: N/A

USACE: We have scanned the book and have a digital copy. We also have the 2-page summaries for each storm as a pdf in our Extreme Strom database. We plan to enter the DAD tables in the database so they can be searched and exported by duration and area for specific regions.

USBR: Yes. We already are, for the most part. Individual DAD tables are digitized as needed. We are collaborating with USACE on this, and supplying many of Reclamation's storm DAD tables that are not in the National Storm Catalog.

NRCS: Probably.

TVA: N/A

NRC: Not sure.

USGS: N/A.

5c.iv Do you consult DAD tables in your safety analyses?

FERC: N/A

USACE: Yes

USBR: Yes.

TVA: N/A

NRC: Seldom.

USGS: N/A.

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5c.v Are storm spatial patterns needed in your safety analyses?

FERC: N/A

USACE: Yes

USBR: Yes, and are required for most watersheds.

TVA: N/A

NRC: Yes.

USGS: N/A.

6 What other extreme precipitation resources does your agency utilize?

NRC: U.S. NRC is seeing a rapidly increasing trend of licensee’s sponsoring “site-specific” PMP studies that involve all of the above. US NRC is faced with reviewing these submittals.

6a Non‐Federal technical documents on extreme storms or PMP?

FERC: No except FERC approved site-specific PMP study results

USACE: For site specific PMP studies, we use the World Meteorologic Organization (WMO) Manual for the Estimate of the Probable Maximum Precipitation.

USBR: We use much of the past and new published literature (journal articles) for methods, ideas, and techniques. We use WMO publications. We use state publications for basic data.

NRCS: Special site specific PMP studies – if accepted by state dam safety agency.

TVA: TVA is currently using extreme storm analyses and site-specific PMP estimates from private consultants.

USGS: There are other studies of storm statistics available for some parts of the country and some studies by USGS. These are used on an individual investigation basis.

6b Other non‐Federal documents?

FERC: No

USACE: Academic research and studies particularly on atmospheric rivers and atmospheric modeling.

USBR: See above answer.

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TVA: TVA is currently using extreme storm analyses and site-specific PMP estimates from private consultants.

USGS: There are some studies of storm statistics by USGS. These are used on an individual investigation basis.

6c Data?

FERC: No

USACE: Precipitation data from USACE, NWS, USGS, CoCoRAS

USBR: We use much data from NCAR, NOAA (CFS-R, other reanalysis), NCDC, and some CoCoRAHs.

TVA: TVA is currently using extreme storm analyses and site-specific PMP estimates from private consultants.

NWS: For developing NOAA Atlas 14, we try to capture precipitation information from as many sources as possible. We then QC the data to derive data sets to be used in analysis. We publish the QC’s data sets on the web.

USGS: Mostly commonly NWS data is used in USGS studies but some local or regional precipitation networks operated by USGS or others could be used.

6d Software?

FERC: No

USACE: USACE uses the HEC-HMR52 program to develop PMP storm events in the Eastern U.S. We also have developed a new tool to provide HMR57 calculations for the Pacific Northwest. Working a new tool called HEC-MetVue to perform storm analysis and combine the HMR computations for various regions of the US. HEC-MetVue will be linked with the HEC-HMS model and the Extreme Storm database.

USBR: We use scripts and capabilities in R, custom FORTRAN programs, etc.

TVA: TVA is currently using extreme storm analyses and site-specific PMP estimates from private consultants.

USGS: There are various software tools and libraries available for analysis of extreme events. The choice of software is a made on an individual investigation basis.

7 Discuss any gaps or further needs

7a What precipitation/extreme storm information do you need that you don’t have now?

FERC: Updated HMRs

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USACE: Need to update the extreme storm database to include more recent extreme storms. We are currently working on this. It would also be good if more atmospheric modeling studies were performed to improve our understanding of the Probable Maximum Precipitation, particularly in the mountainous west.

USBR: We could use an updated extreme storm data base with spatial information, such as an update to Shipe and Riedel (1976). We could use improved methods for combining estimates from atmospheric models (e.g. WRF) with gage-based techniques. Uncertainty of the precipitation field (magnitudes and probabilities) in space and time would be a nice enhancement. Hydrometeorological definition of explicit and implicit stochastic storm transposition would be valuable.

NRCS: Updated PMP estimates.

NRC: U.S. NRC faces several challenges that include: 1) age and limitations of NWS’s HMR reports that are referenced in our general guidance, 2) lack of an overall framework and practical experience for PFHA given the diversity of data and approaches (see below) and 3) a lack of established approaches to appropriate peer review of individual studies given the paucity of experts in the field.

In our view an overall framework for extreme precipitation estimates (and PFHA in general) is lacking. By framework, we mean a structured approach that includes formal consideration of both aleatory and epistemic uncertainties and formal consideration of all technically defensible interpretations of data, models, and methods.

Lastly, we are being pushed to consider the potential for accelerated climate change to affect hazard assessments (for specific facilities), including hazards due to extreme precipitation. There seems to be little definitive information at the site or even regional scale upon which to base guidance.

USGS: The USGS has no official position.

7b For data gaps, what is the most pressing piece of information that needs to be created or updated?

FERC: The historical extreme storms that have occurred after the HMRs were published.

USACE: Depth-Area-Reduction curves in TP40 are typically applied across the U.S. and are often applied to watersheds greater than 400 square miles. Up-to-date area-reduction information is needed as well as guidance for developing hypothetical storm events.

USBR: Improved techniques for spatial patterns in orographic terrain, and defining extreme storm moisture pathways within the intermountain west.

NRCS: Updated PMP estimates and accompanying background information such as historical extreme storms database.

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TVA: Critical review and evaluation of historic extreme storm analysis performed by others, with usage of such as deemed appropriate.

NRC: Data collection and analysis of significant storms seems to be the most pressing data gap. Such information would be needed to 1) simply update PMPs using existing methods; 2) update PMPs with modified methods; or 3) develop a probabilistic alternative to PMP.

USGS: The USGS has no official position.

8 Please identify Agency representatives and other attendees willing to participate in the Extreme Storm Events Work Group’s Writing Workshop, currently scheduled for May 15‐16, 2014, in Washington, D.C., either on‐site or remotely via webinar. Please include contact information.

FERC: Ken Fearon; on-site; kenneth.fearon@ferc.gov, 202/502-6015

Samuel Lin; on-site; Shyangchin.Lin@FERC.gov; 202/502-8881

Other potential FERC Regional Office participants via webinar

USACE: Doug Clemetson – douglas.j.clemetson@usace.army.mil 402-995-2340

Chandra Pathak – chandra.s.pathak@usace.army.mil 202-761-4668

USBR: Victoria Sankovich-Bahls vsankovich@usbr.gov 303-445-2474

John England jengland@usbr.gov 303-445-2541

NRCS: Claudia C. Hoeft (Claudia.hoeft@wdc.usda.gov) 202-720-0772;

Others by webinar (unknown at this time)

TVA: Michael Eiffe, P.E. Program Manager, Hydrology, TVA, 400 W. Summit Hill Drive, WT 10C, Knoxville, TN 37902, (865) 632-3074

NRC: Yuan Cheng, yuan.cheng@nrc.gov, 301-415-1212

Fernando Ferrante, Fernando.Ferrante@nrc.gov, 301-415-8385

Joseph Kanney, joseph.kanney@nrc.gov, 301-251-7600

Thomas Nicholson, Thomas Nicholson@nrc.gov, 301-251-7498

Kevin Quinlan, Kevin.Quinlan@nrc.gov, 301-415-6809

Elena Yegorova, Elena.Yegorova@nrc.gov, 301-251-7454

USGS: Robert Mason, rrmason@usgs.gov

William H. Asquith, wasquith@usgs.gov

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APPENDIX C

Advisory Committee on Water Information (ACWI) Subcommittee on Hydrology (SOH)

Extreme Storm Events Work Group (ESEWG)

State Dam Safety Agency Questionnaire Preamble: Extreme storm hydrometeorology studies impact extreme flood estimates and assessments for dams, nuclear power plants, levees, and other high-hazard structures within the United States. Additionally, environmental impacts from extreme storm events are of increasing concern. The Extreme Storm Events Work Group (ESEWG) is responsible for coordinating studies and databases for reviewing and improving methodologies and data collection techniques used to develop design precipitation estimates of large storm events up to and including the Probable Maximum Precipitation (PMP). The charter for the ESEWG states that it will develop a detailed scope of work/plan of study and determine the necessary funding requirements to update the Catalog of Extreme Storms and Hydrometeorological Reports (HMR). The Work Group is also tasked with developing a list of individual Federal Agency extreme storm product needs. From ongoing discussions and recent advances to probabilistic methodologies for risk-assessment, it is evident that updates to the Catalog of Extreme Storms and HMRs may not fully address the national needs. Therefore, the purpose of this survey is to help the ESEWG identify States’ needs for updating extreme storm products. The following questionnaire asks each State to critically evaluate their views, methods, data sources, tools, etc. regarding extreme storm events and to identify their needs and/or gaps in extreme storm event information. In a Writing Workshop scheduled for Spring 2014, the ESEWG will define extreme storm product(s) that meet the needs of the participating ACWI/SOH/ESEWG member agencies for deterministic and risk-informed infrastructure design. The ESEWG will consider the needs of the States, in part determined from State responses to this questionnaire, in defining extreme storm product(s). The product(s) with corresponding schedule(s) and resource cost(s) will be presented in a proposal to the ACWI/SOH. Based upon a recommendation from State dam officials, the ESEWG reviewed FEMA Document P-919, “Summary of Existing Guidelines for Hydrologic Safety of Dams” (2012) during preparation of the current questionnaire. The ESEWG considers its questionnaire to be more narrowly focused on Extreme Precipitation needs than the previous FEMA survey which more broadly addressed spillway sizing. Because of its merits, the ESEWG will utilize FEMA P-919 to inform the writing of the extreme storm product proposal. 1. Please discuss your State/agency’s extreme precipitation needs for decision making,

assessments, and designs (extreme precipitation is defined as those events with a return period of 1,000-years or greater up to and including PMP):

a. What agencies in your State use extreme precipitation data? (please provide contact information for other interested agencies, if possible)

b. What extreme precipitation data do you use in your decisions? c. How is this extreme precipitation data used?

Workshop Questionnaire for States’ Needs in Extreme Precipitation (continued)

2

d. What is the scale and resolution of this data (regional, site-specific, watershed-specific)?

e. What is the spatial extent to which this data is applied? f. Would it be beneficial if this data were updated? And why is that? g. What are the current statutes, regulations, and court rulings regarding extreme

precipitation data and methods that apply to your State/agency? h. Would current statutes, regulations and court rulings allow use of extreme storm

products other than NOAA HMR PMP? i. If changes to law or regulations would be needed to allow new use of extreme

storm products, describe the revision process. j. Would your State/agency benefit from updated Federal guidelines regarding the

application of new extreme storm products? (e.g. revised FEMA National Dam Safety Program guidelines for Spillway Sizing for dams)

2. Please comment on methods allowed or used by your State/agency to determine

extreme precipitation for decision making, assessments, and designs. Please comment on the applicability of each method and on regulations governing each method:

a. HMRs for PMP? b. Frequency precipitation? c. Site Specific PMP studies? d. Probabilistic Flood Hazards Approach / Risk-informed decision making? e. Streamflow frequency analysis? f. Paleo-hydrology studies? g. If possible, comment on the relevancy of FEMA Publication 919 “Summary of

Existing Guidelines for Hydrology Safety of Dams” with respect to summarizing your State/agency’s extreme precipitation methods and needs.

3. Please describe your State/agency’s views and priorities regarding alternatives to

traditional PMP: a. Continued use of PMP, or alternatives? b. Have you attempted to use numerical models? Please provide any

documentation of the analysis. c. Assessment of radar accuracy? d. Estimating probabilities of extreme rainfall? e. Storm-based analyses? f. Historical database of information on storms and floods?

Specifically regarding risk-based alternatives to traditional PMP, FEMA P-919 reports that 51% of respondents had concerns regarding the use of risk analysis to determine spillway size requirements for dams. At the same time, FEMA P-919 reports 31% of respondents agreed with the statement that designing for the PMP/PMF is unreasonably conservative. FEMA P-94, “Selecting and Accommodating Inflow Design Floods for Dams” (2013), recommends risk-informed decision making as one alternative approach to spillway sizing (NOTE: prescriptive application of the PMF is another recommended alternative), and FEMA P-919 reports that

Workshop Questionnaire for States’ Needs in Extreme Precipitation (continued)

3

many States would be more receptive to adopting risk-based design criteria if Federal dam agencies could agree on standards.

4. Considering the previously mentioned information from FEMA, if a probability or risk-based extreme storm product is developed:

a. Would your State/agency be receptive to implementing the new product? b. Would your State/agency still need updated PMP? c. How important would it be that risk-based products could be readily used by your

existing staff without requiring additional expertise? d. How important would it be that such products be accompanied by new Federal

guidelines for application (e.g. Risk-based guidelines for spillway sizing)? 5. Please describe the importance your State/agency places on having a consistent

national standard for extreme storm products and having Federal guidelines for such products:

a. In regard to methods and data, is there a need for a national standard? Is there a need for Federal guidelines?

b. In regard to interpretation of risk, is there a need for national standards and Federal acceptance?

c. In regards to Site Specific PMP studies, is there a need for national standards and Federal guidelines?

d. In regards to consistent instructions on how to use and apply extreme storm products?

e. In regards to the need for extreme storm products to have a consistent level of risk across spatial domains (both between states and within states)?

6. Please discuss applicability of current Federal extreme precipitation publications,

databases and tools: a. Hydrometeorological Reports

i. Which HMR do you use most frequently? ii. What information do you glean from the HMRs? And how do you use this

information exactly? iii. Which information is most useful? iv. Do you use the spatial and temporal storm patterns provided? v. Do you use the DAD tables? vi. Do you use the HMRs to compute PMP? vii. Do you use the HMRs to compute a percentage of PMP? Which

percentage and what is the basis for reducing PMP? viii. Do you use the areal reduction factors provided in the HMRs? ix. Do you consider storm seasonality in your studies? x. Are the HMRs easy to use? If not, why? xi. What would you change about the HMRs when/if updated? xii. What additional information would you want to see included? xiii. Do you associate a probability to PMP? If so, describe your

methodology.

Workshop Questionnaire for States’ Needs in Extreme Precipitation (continued)

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xiv. Is updating the HMRs a priority to your State/agency? xv. Would your State/agency be interested in contributing to a Federal effort

to update PMP? (Data, technical, financial, review, etc.) b. Precipitation-frequency products:

i. NOAA Atlas 14 is being updated to include the Northeastern States (from TP40). Funding has not yet been found to update estimates for Texas (from TP40) or the Northwestern states (From NA2). How important is it to your State/agency to have NOAA Atlas 14 volumes for Texas and the Northwestern states?

ii. Do you consult NOAA Atlases 2 and 14? For what reason, exactly? iii. Which return period(s) is most useful for your studies? iv. Do you extrapolate beyond the 1,000-year return period (not

recommended by NWS)? If so, how? v. Do you currently compute areal estimates based on the point values from

NOAA Atlas 2 or 14? If so, how? And where/how do you obtain your areal reduction factors if you use that method?

vi. Does your State feel there is a need to update areal reduction factors for frequency storms?

vii. To what extent is NOAA Atlas 14 information incorporated into design guidance or regulations that govern what you do?

viii. Are there elements in NOAA Atlas 2 or TP 40 missing in NOAA Atlas 14? ix. Is NOAA Atlas 14 easy to use? How could it be improved? x. Do you input latitude/longitude values into the web interface? xi. Do you consult the isopluvial maps of precipitation frequency estimates

for a particular exceedance probability and duration? If so, what value do they provide beyond the GIS compatible grids of the same information?

xii. Of what value are the temporal distribution curves in NOAA Atlas 14? xiii. Of what value are the seasonal curves in NOAA Atlas 14? xiv. There is a difference between precipitation frequency estimates more

frequent than about 15-20 years ARI for estimates derived from annual maximum series and estimates derived from partial duration series. How important is it for NOAA Atlas 14 to provide both? Which of the two is your preference and why?

xv. Do you consult the report documentation of NOAA Atlas 14 for any purpose?

xvi. Do you use any of the background information that the NWS used to compute the precipitation frequency estimates? If so, what exactly? (e.g., gauge data, clusters)

7. What other extreme precipitation resources does your State/agency utilize?

a. Non-Federal technical documents on extreme storms or PMP? b. Other non-Federal documents? c. Data? d. Software?

Workshop Questionnaire for States’ Needs in Extreme Precipitation (continued)

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8. Please describe ongoing and planned efforts in your State to update PMP or develop new extreme storm products?

9. Please discuss any gaps or further needs: a. What precipitation/extreme storm information do you need that you don’t have

now? b. For data gaps, what is the most pressing piece of information that needs to be

created or updated?

10. Please identify State’s representatives and other attendees willing to participate in the Extreme Storm Events Workgroup’s Writing Workshop, currently scheduled for May 15-16, 2014, in Washington, D.C., either on-site or remotely via webinar? Please include contact information. The current Workshop agenda includes time for the States to share their perspectives on current applications of extreme precipitation data and methods, and there will be opportunities for State input to help define extreme storm product needs and possible State contributions.

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APPENDIX D

Advisory Committee on Water Information (ACWI) Subcommittee on Hydrology (SOH)

Extreme Storm Events Work Group (ESEWG)

Summary of Questionnaire Responses by State Dam Safety Agencies1

1. Discuss your State/agency’s extreme precipitation needs for decision making, assessments, and designs (extreme precipitation is defined as those events with a return period of 1,000-years or greater, up to and including PMP):

a. What agencies in your State use extreme precipitation data? The dam safety agencies at the state-level (e.g., Division of Dam Safety, Dam Safety Section, Safety of Dams Program) use extreme precipitation data.

b. What extreme precipitation data do you use in your decisions? • PMP, 1/3 PMP, 1/2 PMP • Precipitation associated with the 100 and/or 1,000-year return period • State-specific and site-specific information • Hydrometeorological Reports • NOAA Atlas 14

c. How is this extreme precipitation data used?

• As design criteria for dams or spillways • Compute the PMF from the PMP; or %PMF from a %PMP • Dam breach inundation studies

d. What is the scale and resolution of this data?

• Watershed-specific • Site-specific • Regional

1 To capture the view of the States’ responses as accurately as possible, the following qualitative indicators were used: • 'Most' indicates a majority ; • 'Some' indicates approximately half; and • 'Few' indicates a minority of responses.

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e. What is the spatial extent to which this data is applied? The spatial extent is determined by the drainage area upstream of a dam, which is commonly less than 10 square miles. The majority of the drainage areas are less than 100 square miles, while few are several hundred square miles in size.

f. Would it be beneficial if this data were updated? And why is that? The States agree that it would be beneficial to update the data. A multitude of reasons were provided in favor of updating the data:

• The data is old, and it is unknown if the data is conservative. • The current data is uncomfortably conservative. • Recent hurricanes and extreme storm events are not included. • Other frequencies have been updated in NOAA Atlas 14. • There is a need for rainfall depth and distribution data for sub-10 square

mile watersheds and short duration storms. • There is a need to understand the influence of climate change on

extreme precipitation. • An update to the HMRs would preclude more complex and subjective

state- and site-specific PMP studies from being performed.

g. What are the current statutes, regulations, and court rulings regarding extreme precipitation data and methods that apply to your State/agency? The States do not have statutes or court rulings to dictate requirements for extreme precipitation data and methods. Most States, however, have regulations or guidelines for dam safety that require the PMF or a percentage thereof, depending on drainage area size and hazard classification, to be used for spillway design.

h. Would current statutes, regulations and court rulings allow use of extreme storm products other than NOAA HMR PMP? Most States prefer the best available data, however, few States have guidelines that dictate that NOAA products must be used.

i. If changes to law or regulations would be needed to allow new use of extreme storm products, describe the revision process. Each State has their own process for revision of regulations. Some require legislature. Few States would prefer for storm products be endorsed by NOAA.

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j. Would your State/agency benefit from updated Federal guidelines regarding the application of new extreme storm products (e.g. revised FEMA National Dam Safety Program guidelines for Spillway Sizing for dams)? Most States agree that it would be beneficial if Federal guidelines were published regarding the application of new extreme storm products. Few States feel that Federal guidelines would assist in selling new products to dam owners and politicians. Few States mention that Federal guidelines would benefit dam owners who are regulated by dual government agencies to prevent conflicting instructions. Few States mention that updating current guidelines takes significant effort.

2. Comment on methods allowed or used by your State/agency to determine extreme

precipitation for decision making, assessments, and designs. Please comment on the applicability of each method and on regulations governing each method:

a. HMRs for PMP? Most States require the use of the HMRs to determine PMP, and the resulting PMF from the PMP.

b. Frequency precipitation? Some States do not use any precipitation frequency information. Other States utilize the 100-, 500-, and/or 1,000-year precipitation events.

c. Site Specific PMP studies? The States are interested in site-specific PMP studies and would consider a study if it were conducted within their region.

d. Probabilistic Flood Hazards Approach / Risk-informed decision making? Most States have not used detailed risk analysis for decision making. Few States have used risk analysis to prioritize dams for rehabilitation or to mitigate a deficiency to ensure dam safety. Few States are not allowed to use risk analysis because it is not included in their guidelines.

e. Streamflow frequency analysis? Some States do not use or allow streamflow frequency analysis. Other States have accepted streamflow frequency analyses where appropriate data existed.

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f. Paleo-hydrology studies? Paleo-hydrology studies have not been conducted by States. However, some States would consider such a study. Few States would not consider a paleo-hydrology study because it is not included in their guidelines.

g. If possible, comment on the relevancy of FEMA Publication 919 “Summary of Existing Guidelines for Hydrology Safety of Dams” with respect to summarizing your State/agency’s extreme precipitation methods and needs. FEMA Publication 919 appears to be relevant to some States, but this publication does not seem to affect the State’s needs and methods.

3. Describe your State/agency’s views and priorities regarding alternatives to traditional

PMP: a. Continued use of PMP, or alternatives?

The States continue to use PMP, either as the full PMP or some percentage of PMP, for spillway design. Few States are considering the use of frequency precipitation (e.g. 1,000- or 2,000-year event) but have not fully implemented this practice.

b. Have you attempted to use numerical models? Please provide any documentation of the analysis. The States have not attempted to use numerical models.

c. Assessment of radar accuracy? Few States have incorporated radar into site-specific PMP studies. None of the States have assessed radar accuracy.

d. Estimating probabilities of extreme rainfall? States currently do not estimate the probability of extreme rainfall. Some States, however, believe that it would be beneficial. Few States don’t feel that it is possible to estimate the probability of extreme precipitation accurately.

e. Storm-based analyses? Few States use storm-based analyses for watershed calibration on rare occasions.

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f. Historical database of information on storms and floods? The States have varied opinions regarding a historical database. Some use historical information for reference but do not think that it is helpful for day-to-day operations. Few States consider a historical database to be high priority, while few States do not consult a historical database on storms and floods.

4. Considering the previously mentioned information from FEMA, if a probability or risk-

based extreme storm product is developed: a. Would your State/agency be receptive to implementing the new product?

Most States would consider implementing the new product if the product was well-prepared and documented and if it was simple to apply. Few States would not implement a new product.

b. Would your State/agency still need updated PMP? Most States would still need an updated PMP.

c. How important would it be that risk-based products could be readily used by your existing staff without requiring additional expertise? Some States prefer a product that worked well with definitive procedures to calculate risk more accurately. Some States, however, view a product that was readily useable as critical. Few States cite that the large number of dams and the availability and accuracy of information is the bigger restraint. Few States point out the need for consultants, as opposed to staff, to be able to use the product.

d. How important would it be that such products be accompanied by new Federal guidelines for application (e.g. Risk-based guidelines for spillway sizing)? Most States believe that a Federal standard would carry more weight and thus be more likely to get accepted. Few States point out that dam owners who are regulated by dual government agencies would benefit from Federal guidelines. Few States do not believe that a Federal standard is important.

5. Describe the importance your State/agency places on having a consistent national standard for extreme storm products and having Federal guidelines for such products:

a. In regard to methods and data, is there a need for a national standard? Some States would find it helpful to have consistent standards for larger, high hazard dams. Few States prefer flexibility to select the best methodologies for their needs and would prefer guidelines, not standards.

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b. In regard to interpretation of risk, is there a need for national standards and Federal acceptance? Most States think a national standard would be beneficial; however, few States are concerned that the thoughts of the individual engineer and state programs could get left behind.

c. In regards to site-specific PMP studies, is there a need for national standards and Federal guidelines? Most States think that national standards would be helpful. Few States indicate that an update to the HMRs would negate the need for more complex and subjective site-specific PMP studies.

d. In regards to consistent instructions on how to use and apply extreme storm products? Most States think that a national standard would be beneficial, especially if the standard could help easily check the validity of the submissions for spillway design.

e. In regards to the need for extreme storm products to have a consistent level of risk across spatial domains (both between states and within states)? Most States think this would be beneficial.

6. Discuss applicability of current Federal extreme precipitation publications, databases

and tools: a. Hydrometeorological Reports

i. Which HMR do you use most frequently? Most States use HMRs 51 and 52 most frequently.

ii. What information do you glean from the HMRs? And how do you use this information exactly? Most States use rainfall depths and temporal distributions provided in the HMRs. Few States use snowmelt parameters and temperature time-series information from HMR 58. This information is used in HEC-1 or HEC-HMS models for spillway design and breach inundation mapping. The snow parameters are used to calculate snowmelt runoff.

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iii. Which information is most useful? Most States indicate the rainfall depths as the most important information. Few States think that all of the information in the HMRs is useful.

iv. Do you use the spatial and temporal storm patterns provided? Most States use the spatial patterns for watersheds larger than 10 square miles. Few States do not use this information.

v. Do you use the DAD tables? The answer to this question was split amongst the States: some States use the DAD tables, and some do not.

vi. Do you use the HMRs to compute PMP? Most States use the HMRs to compute PMP.

vii. Do you use the HMRs to compute a percentage of PMP? Which percentage and what is the basis for reducing PMP? Most States only use percentages of the PMF after it is determined by 100% of the PMP.

viii. Do you use the areal reduction factors provided in the HMRs? Most States use the areal reduction factors.

ix. Do you consider storm seasonality in your studies? Most States do not use storm seasonality.

x. Are the HMRs easy to use? If not, why? Most States believe that the HMRs are fairly easy to use. Few States would like to see an easy GIS software program that would compute rainfall distributions and amounts. Few States indicate that the HMRs are unclear for short duration or small area sizes (less than 10 square miles).

xi. What would you change about the HMRs when/if updated? • Easy GIS program • Address sub-10 square mile watersheds • Address short duration storms • Web-based application that could delineate watershed and

calculate PMP (similar to USGS StreamStats or NOAA Atlas 14)

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• Web-based application to download results in GIS layer or tabular format

• Demonstration of how rainfall and temporal distributions were derived

xii. What additional information would you want to see included? • Sub-10 square mile watersheds • Instruction for computation of temporal distribution • Better documentation of the supporting data and any subjective

judgment that went into the analysis

xiii. Do you associate a probability to PMP? If so, describe your methodology. Most States do not associate a probability to PMP. Few States extend frequency plots (using a Pearson Type III probability distribution) for an estimate of the corresponding return period.

xiv. Is updating the HMRs a priority to your State/agency?

The answer to this question is split amongst the States: some States think that an update to the HMRs is a priority, while some do not.

xv. Would your State/agency be interested in contributing to a Federal effort to update PMP? (Data, technical, financial, review, etc.) Most States would consider contributing to a Federal effort to update PMP.

b. Precipitation-frequency products: i. NOAA Atlas 14 is being updated to include the Northeastern States

(from TP40). Funding has not yet been found to update estimates for Texas (from TP40) or the Northwestern states (From NA2). How important is it to your State/agency to have NOAA Atlas 14 volumes for Texas and the Northwestern states? Most States do not believe an update for Texas or for the Northwestern states is important.

ii. Do you consult NOAA Atlases 2 and 14? For what reason, exactly? Most States consult NOAA Atlas 14.

• 24-hour, 100-year values

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• 6-hour, 100-year values • Rainfall distributions • Consulted for design considerations, • To assess the potential for erosion near the dam and receiving

channel • To check the reasonableness of PMP estimates and/or site-

specific PMP estimates.

iii. Which return period(s) is most useful for your studies? • 2-year • 5-year • 25-year • 100-year • 1,000-year

iv. Do you extrapolate beyond the 1,000-year return period (not

recommended by NWS)? If so, how? Most States do not extrapolate beyond the 1,000-year return period. Few States will apply a Pearson Type III distribution to maximum precipitation data.

v. Do you currently compute areal estimates based on the point values from NOAA Atlas 2 or 14? If so, how? And where/how do you obtain your areal reduction factors if you use that method? Most States do not need areal reduction factors because the watersheds are small. If an areal reduction is needed, the HMRs are consulted.

vi. Does your State feel there is a need to update areal reduction factors for frequency storms? Some States did not have an answer to this question. Few States thought this could be a need.

vii. To what extent is NOAA Atlas 14 information incorporated into design guidance or regulations that govern what you do? Some States use NOAA Atlas 14 information, but NOAA Atlas 14 is not incorporated into States’ guidance or regulations. The information that is referenced include: 5-year, 25-year, 100-year storms at the 24-hour duration and the 1,000-year event.

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viii. Are there elements in NOAA Atlas 2 or TP 40 missing in NOAA Atlas 14?

The States were not aware of any missing elements.

ix. Is NOAA Atlas 14 easy to use? How could it be improved? Most States find NOAA Atlas 14 to be easy to use. Few States found it difficult to import the rainfall distributions into hydrology models. Few States were interested in the precipitation stations that were used in the regional precipitation-frequency calculations.

x. Do you input latitude/longitude values into the web interface? Most States enter in latitude/longitude. Few States navigate by the map interface.

xi. Do you consult the isopluvial maps of precipitation frequency estimates for a particular exceedance probability and duration? If so, what value do they provide beyond the GIS compatible grids of the same information? The States do not use this feature.

xii. Of what value are the temporal distribution curves in NOAA Atlas 14? Most States find the temporal distribution curves to be of little value.

xiii. Of what value are the seasonal curves in NOAA Atlas 14? The States find the seasonal curves to be of little value.

xiv. There is a difference between precipitation frequency estimates more frequent than about 15-20 years ARI for estimates derived from annual maximum series and estimates derived from partial duration series. How important is it for NOAA Atlas 14 to provide both? Which of the two is your preference and why? The States do not have an opinion on this issue at this time; however, it was indicated by few States that both need not be provided but rather an explanation be included for the one that was provided.

xv. Do you consult the report documentation of NOAA Atlas 14 for any purpose?

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Most States do not consult the report documentation. Few States refer to the documentation to understand the methodology that was implemented.

xvi. Do you use any of the background information that the NWS used to compute the precipitation frequency estimates? If so, what exactly? (e.g., gauge data, clusters) The States do not use the background information.

7. What other extreme precipitation resources does your State/agency utilize?

a. Non-Federal technical documents on extreme storms or PMP? None.

b. Other non-Federal documents? None.

c. Data? None.

d. Software? Few States use software provided by NRCC.

8. Describe ongoing and planned efforts in your State to update PMP or develop new extreme storm products?

• Possible revision of use of percentages of the PMP to using 1,000-year and 2,000-year floods generated by statistical analyses

• Case by case studies of site-specific PMP • State-wide PMP study • Revision of the Dam Hazard Classification evaluation procedure to include more

risk-informed decision-making or criteria • Potential modification to the selection of design frequency storms for each dam

hazard classification • Revision of regression equations for determining basin unit hydrograph

parameters

9. Discuss any gaps or further needs: a. What precipitation/extreme storm information do you need that you don’t

have now?

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• Information regarding developing and using frequency based extreme precipitation

• Updates of existing storm information • HMR 52 software in GIS format

b. For data gaps, what is the most pressing piece of information that needs to be created or updated?

• Information regarding developing and using frequency based extreme precipitation

• New rainfall estimates in HMR 51 • Methods for applying rainfall to a watershed

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Subcommittee on Hydrology (SOH) Extreme Storm Events Work Group (ESEWG)

APPENDIX E

Program & Agenda – Workshop to Define Needed Extreme Storm Products

Workshop Date: May 15, 2014

Workshop Location: NOAA, National Weather Service Headquarters (adjacent to the Silver Spring METRO Station) at 1325 East-West Highway Room 14316, Silver Spring, MD 20910

All Attendees (Visitors and Remote Participants) by Tuesday 5/13 12PM EDT: 1) Must register for the workshop through the registration link. 2) In addition, those participating remotely via GoToMeeting must also register

https://www1.gotomeeting.com/register/360602705 to get instructions via email from RES Organizer with subject title: Confirmation SOH-ESEWG Workshop…on how to remotely log into the meeting. The email from RES Organizer is a unique connection for each remote participant and should NOT be shared. During the day of the conference at 745AM Eastern, we ask that you (a) use the hyperlink provided by RES Organizer from your PC, (b) dial in via phone to the special number provided to you, (c) announce your name and affiliation on the phone, (d) put your phone on mute, and (e) if you have any questions during the meeting, please type into the question window box so that all attendees can see your posting.

Workshop Objective:

Clearly define extreme storm products that are needed for deterministic and risk-informed infrastructure decision making by Federal agencies, now and in the future.

Goal:

• Refine the extreme storm information and methodology needs of each Federal agency that participates in the ACWI-SOH ESEWG.

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Workshop Agenda

Thursday, May 15th (NOTE: All Times Shown Are In Eastern Daylight Time)

7:30 a.m. EDST Visitor Arrival at NOAA/NWS and Security Check-In

7:45 Remote Participants Login/Call-in per unique Instructions emailed by RES Organizer

8:00 Welcome and Opening Remarks ……….. Victor Hom, ACWI-SOH Chair, NOAA, National Weather Service

8:10 Introductions …………………. Tom Nicholson, ESEWG Chair, U.S. NRC

8:20 Overview of Workshop Objective, Goal, Activities and Expected Products ……………………………………. Victoria Sankovich-Bahls, U.S. Bureau of Reclamation

8:30 Current Application of Extreme Precipitation Data and Information [each Federal agency will address Federal questionnaire (please see attachment #1)]

• (8:30-9:00) Natural Resources Conservation Service – Claudia Hoeft • (9:00-9:15) U.S. Geological Survey – Robert Mason • (9:15-9:45) Federal Energy Regulatory Commission – Ken Fearon & Samuel Lin

9:45 a.m. Break (30 Minutes)

• (10:15-10:45) U.S. Nuclear Regulatory Commission – Joseph Kanney • (10:45-11:15) Tennessee Valley Authority – Mike Eiffe • (11:15-11:45) NOAA/National Weather Service – Geoffrey Bonnin • (11:45-12:15) Federal Emergency Management Agency – (INVITED)

12:15 p.m. LUNCH (60 Minutes) at NOAA BLDG 3 Cafeteria or Local Eateries

1:15 p.m. NOAA GATEWAY EXHIBITS (Ground Floor)

1:30 p.m. Current Application of Extreme Precipitation Data and Information (continued)

• (1:30-2:15) U.S. Army Corps of Engineers – Doug Clemetson and Aaron Byrd • (2:15-3:00) U.S. Bureau of Reclamation – John England and Victoria Sankovich-Bahls

3:00 p.m. Break (15 Minutes)

3:15 Current Application of Extreme Precipitation Data and Information States’ perspectives [each State will have 15 minutes to address their responses to the States’ questionnaire (please see attachment #2)]

• (3:15-3:30) Opening Comments from Panel Moderator: – Mark Perry, Dam Safety Engineer, State of Colorado

• (3:30-5:00) State Dam Safety Engineers from CO, PA and (CA, AZ, VA, remotely)

5:00 Closing Remarks …………………. Tom Nicholson, ESEWG Chair, U.S. NRC

5:15 p.m. Adjourn

APPENDIX F Attendees – Workshop to Define Needed Extreme Storm Products

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Registered Attendees Onsite Organization

William Asquith X U.S. Geological Survey

Geoff Bonnin X NOAA/National Weather Service

Aaron Byrd X U.S. Army Corps of Engineers

Li-Chuan Chen X Climate Prediction Center/NCEP/NWS/NOAA

Doug Clemetson X U.S. Army Corps of Engineers

Michael Eiffe X Tennessee Valley Authority

John England X U.S. Bureau of Reclamation

Kenneth Fearon X Federal Energy Regulatory Commission

Claudia Hoeft X Natural Resources Conservation Service (NRCS)

Victor Hom X NOAA/National Weather Service

Joseph Kanney X U.S. NRC/Office of Nuclear Regulatory Research

Bill Kappel X Applied Weather Associates

Samuel Lin X Federal Energy Regulatory Commission

Pat Madden X U.S. NRC/Office of Nuclear Regulatory Research

Robert Mason X U.S. Geological Survey

Ron Mease X PA Department of Environmental Protection/Division of Dam Safety

Thomas Nicholson X U.S. NRC/Office of Nuclear Regulatory Research

William Ott X U.S. NRC/Office of Nuclear Regulatory Research

Sanja Perica X NOAA/National Weather Service

Mark Perry X Colorado Division Water Resources/Dam Safety

Victoria Sankovich-Bahls X U.S. Bureau of Reclamation

Ed Tomlinson X Applied Weather Associates

John Weatherly X U.S. Army Corps of Engineers, ERDC

Elena Yegorova X U.S. NRC/Office of Nuclear Regulatory Research

APPENDIX F Attendees – Workshop to Define Needed Extreme Storm Products

2

Registered Attendees Offsite Organization

Robert Bennett X Virginia Department of Conservation Recreation

Bud Brock X New Mexico Dam Safety Bureau

Sushil Chaudhary X Office of State Engineer, State of New Mexico

Melissa Collord X CA Department of Water Resources

Brian Shane Cook X Dam Safety and Floodplain Compliance

Guy Hoyle-Dodson X Washington State Dept. Of Ecology, Dam Safety Office

Bruce Harrington X MD Dept. of the Environment/Dam Safety Division

James Head X New Mexico Office of the State Engineer

Stuart Henry X Barge Waggoner Sumner and Cannon, Inc.

Michael Johnson X State of Arizona DWR

Michele Lemieux X Montana Dam Safety Program

Paul Marinelli X Mass DCR-Office of Dam Safety

Dusty Myers X Chief, Dam Safety Div./MS Dept. Environmental Quality

Mark Ogden X Association of State Dam Safety Officials (ASDSO)

Will Thomas X Michael Baker International

Charles Thompson X New Mexico Office of the State Engineer

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Subcommittee on Hydrology (SOH) Extreme Storm Events Work Group (ESEWG)

APPENDIX G

Presentations

Workshop to Define Needed Extreme Storm Products

Current Application of Extreme Precipitation Data and Information

• Natural Resources Conservation Service – Claudia Hoeft

• U.S. Geological Survey – Robert Mason

• Federal Energy Regulatory Commission – Ken Fearon & Samuel Lin

• U.S. Nuclear Regulatory Commission – Joseph Kanney

• Tennessee Valley Authority – Mike Eiffe

• NOAA/National Weather Service – Geoffrey Bonnin

• U.S. Army Corps of Engineers – Doug Clemetson and Aaron Byrd

• U.S. Bureau of Reclamation – John England & Victoria Sankovich-Bahls

• State of Colorado Perspective – Mark Perry, Dam Safety Engineer, State of Colorado

• State Dam Safety Engineers from CO, PA and (CA, AZ, VA, remotely)