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Rainfall Atlas 14: Replacement of Technical Paper 40

Case Studies and Implications

Presentation to the Minnesota Water Resources Conference

October 15, 2013 Karen Chandler


outline

1. TP-40 (the old Atlas) 2. Atlas 14 3. TP-40/Atlas 14 comparisons 4. Rainfall distributions for Atlas 14 5. Atlas 14 case studies 6. Atlas 14 implications 7. questions/discussion

Steve Buan National Weather Service, NOAA


1. Technical Paper 40 (TP-40)

• key document for hydrologists and water planners, created by NOAA in 1961

• developed using available rainfall information from far fewer stations than exist today

• included the “dust-bowl” years of the 1930’s • gives rainfall data for entire country

– rainfall frequency or recurrence intervals: 1-, 2-, 5-, 10-, 25-, 50-year, and 100-year events

– rainfall durations: 30-m, 1-h, 2-h, 3-h, 6-h, 12-h, 24-h, 2-d, and 4-d events


1. Technical Paper 40 (TP-40)


2. Atlas 14 (the new TP-40)

11 states (dark blue) pooled funds to update

Source: NOAA, peer technical review document



TP-40 Minnesota daily stations Atlas 14 Minnesota daily stations



TP-40 Minnesota sub-daily stations Atlas 14 Minnesota sub-daily stations



• average record length now over 50 years – more than double the record used in original studies – oldest Minnesota data set from 1836 (Ft. Snelling /

Minneapolis St. Paul Airport)


2. Atlas 14: improved usability

• interactive web interface ‒ click to a

specific point: no more estimating

‒ http://dipper.nws.noaa.gov/hdsc/pfds/

http://dipper.nws.noaa.gov/hdsc/pfds/





• station data provided in downloadable tabular form

• over 190 storms



• or as depth-duration-frequency graphs


3. TP-40/Atlas 14 comparisons

• many significant increases: e.g., Minneapolis, MN - 6.0 to 7.5 inches (+25%)

• some decreases for certain storms central Minnesota

• degree of change tends to increase as storm frequency decreases

MSP International AP

Frequency % Change 2 0 5 -3

10 0 50 21

100 25


St. Cloud (Frequency) (%Change) 2 4 5 0 10 -2 50 8 100 10

Minneapolis/St. Paul (Frequency) (%Change) 2 0 5 -3 10 0 50 21 100 25


Albert Lea (Frequency) (%Change) 2 0 5 0 10 5 50 21 100 24


Duluth Airport (Frequency) (%Change) 2 8 5 0 10 3 50 17 100 19


Alexandria (Frequency) (%Change) 2 4 5 -6 10 -5 50 2 100 7

Moorhead (Frequency) (%Change) 2 9 5 0 10 6 50 22 100 23


3. Atlas 14/TP 40 comparison

• Twin Cities Metro area – 100-year,

24-hour event


4. Review /compare rainfall distributions

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Frac

tiona

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SCS Type II


4. “nested” distribution

• hypothetical precipitation distribution

• point-specific • embeds precip depths for

multiple durations (e.g., 5-min, 1-hour, 24-hour, etc.)

• each return frequency has a different distribution (e.g., 10-year or 100-year)

• multiple storms “nested” within single distribution

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4. creating “nested” distribution Twin Cities example

Duration Unit Duration (hours)

Depth (inches)

Percent of Storm Depth

5 minutes 0.083 1.02 14% 10 minutes 0.167 1.49 20% 15 minutes 0.25 1.82 24% 30 minutes 0.5 2.63 35% 60 minutes 1 3.70 49% 2 hours 2 4.77 64% 3 hours 3 5.53 74% 6 hours 6 6.58 88%

12 hours 12 7.12 95% 24 hours 24 7.49 100%



Depth (inches)



12 hours 12 7.12 95% 24 hours 24 7.49 100%



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5-minute storm 1.02”, 14%

5 minutes



Depth (inches)



12 hours 12 7.12 95% 24 hours 24 7.49 100%



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3-hour storm

5.53”, 74%

3 hours



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4. Atlas 14 quartile storms (NOAA)

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FirstQuartile

SecondQuartile

ThirdQuartile

FourthQuartile

• NOAA provided 4 quartile storms for Atlas 14

• similar to Huff distributions

• most rainfall falls in respective quartile

• most MN storms are 1st or 2nd quartile


4. Comparison of 24-hour rainfall distributions

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SCS Type II

Nested



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SCS Type II

Nested



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Nested



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Nested



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SCS Type II

Nested


4. peak rainfall intensity of storms

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SCS Type II(TP40)

FirstQuartile

SecondQuartile

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FourthQuartile

SCS Type II(Atlas 14)

Nested

Peak

rain

fall

inte

nsity

(in

/hr)

Comparison of peak rainfall intensity for the 100-year, 24-hour storm


4. draft NRCS regional Atlas 14 distributions

• NRCS considering regionalized distributions for Minnesota

• likely 2 distributions for entire state: – #3: most of MN – #4: arrowhead


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Draft NRCS Type 3

Draft NRCS Type 4

Old SCS Type II

4. draft NRCS regional Atlas 14 distributions

both draft distributions are more intense than old SCS Type II


5. case studies: 3 examples

A. North Creek: Vermillion River Watershed B. Lake Cornelia/Lake Edina: Nine Mile Creek

Watershed C. Proposed residential development pond:

Coon Creek Watershed


5. H&H modeling to compare distributions

Model Number of

subwatersheds Model area

(acres)

Average subwatershed

size (acres)

Impervious percentage

(%) A. North Creek (tributary to Vermillion River)

154 8,431 55 13

B. Lake Cornelia/Lake Edina 230 1,474 6 41

C. Residential Pond 1 15 15 43


5.A. North Creek modeling

• Compared – Rainfall intensities for different distributions – Discharge changes at watershed outlet for 24-

hour 100-year storm


5.A. comparison of TP40 and Atlas 14 rainfall depths (North Creek)

Duration (hours)

TP40 Depth (in)

Atlas 14 Depth (in)

6 4.50 6.70

12 5.30 7.05

24 6.00 7.42


5.A. peak rainfall intensity (North Creek)

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SCS Type II(TP40)

FirstQuartile

SecondQuartile

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FourthQuartile


Nested

Peak

rain

fall

inte

nsity

(in

/hr)

Comparison of peak rainfall intensity for the 100-year, 24-hour storm


5.A. watershed outlet hydrograph comparison for 24-hour, 100-year storm (North Creek)

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North Creek Watershed Outlet Hydrographs

SCS Type II(TP40)



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Nested



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North Creek Watershed Outlet Hydrographs First Quartile

SCS Type II(TP40)


Nested



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Nested


5.A. Watershed outlet hydrograph comparison for 24-hour, 100-year storm (North Creek)

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SCS Type II(TP40)


Nested



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Fourth Quartile

SCS Type II(TP40)SCS Type II(Atlas 14)Nested


5.A. North Creek modeling summary

• nested distribution produced highest peak discharge at watershed outlet (13 sq mi) for 100-year, 24-hour storm


5.B. Lakes Edina-Cornelia modeling

• compared runoff depth • compared peak

subwatershed runoff rate changes

• compared peak elevations for lakes


5.B. average runoff depth from pervious area (Edina-Cornelia)

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SCS Type II(TP40)

FirstQuartile

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FourthQuartile


Nested

Run

off D

epth

(inc

hes)

Comparison of average subwatershed runoff depth for 100-year, 24-hour storm


5.B. pervious area peak runoff rate: average change from SCS Type II – TP40

-100%

-80%

-60%

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-20%

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60%

First Quartile SecondQuartile

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e (A

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)

Comparison of average subwatershed pervious area peak runoff rate For 100-year, 24-hour storm


5.B. lake elevation change from SCS Type II - TP40, 100-year, 24-hour event

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)

Lake Edina

24-hour



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North Cornelia

24-hour



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South Cornelia

24-hour


5.B. Lake Edina / Lake Cornelia modeling summary

• nested distribution produces highest average runoff depth and peak discharges for subwatersheds

• lake level impacts – peak lake elevations vary less than subwatershed

peak discharges – nested distribution produces highest lake

elevations


5.C. residential development rate control pond

• north metro development (Coon Creek) • Coon Creek WD managing to Atlas 14 • includes rate control pond and several WQ

BMPs • 15 acres tributary to rate control pond, 43%

impervious • modeled Atlas 14 and TP-40 depths using SCS

Type II


5.C. residential development rate control pond

• result: houses elevated additional half a foot to achieve required freeboard

100-Year, 24 Hour Storm

Rainfall Depth (in)

Pond Elevation

(feet)

TP-40 5.8 897.34

Atlas 14 7.17 897.91


6. implications for water planners, designers, and regulators

• when to start using Atlas 14 numbers? • what storm distribution should be used? • changes to permitting, ordinances, policies, and standards • legal implications of using or not using Atlas 14 results

Barr Engineering Utica Ravine stabilization project in Savage, MN



• difference between 10- and 100-year events are greater: existing municipal storm sewer may not be undersized, but flood control could be undersized

http://minnesota.publicradio.org/display/web/2010/06/25/severe-weather http://minnesota.publicradio.org/display/web/2010/06/25/severe-weather



• rate control ponds may be undersized

• flood protection: future FEMA DFIRM mapping and levee certifications may be affected (levee interior drainage, lake studies)

http://minnesota.publicradio.org/display/web/2010/06/25/severe-weather


6. implications: possible approaches for water planners, designers, and regulators

• adjust freeboard requirements • take advantage of opportunities to mitigate

impacts: – safe overflow routes – increase storage – larger easements

Thompson Lake rainwater garden

http://www.dakotacountyswcd.org/pdfs/sw_retrofit_plan_full.pdf


Rainfall Atlas 14: Replacement of Technical Paper 40

Implications and Case Studies

Presentation to the Minnesota Water Resources Conference

October 15, 2013 Karen Chandler

questions?

COMMUNITY STORMWATER RESPONSE TO A CHANGING LANDSCAPE AND CLIMATE: A FRAMEWORK FOR ADAPTATION PLANNING AND IMPLEMENTATION

Trisha Moore, John Gulliver (University of Minnesota), Leslie Yetka (Minnehaha Creek Watershed District), James Gruber (Antioch University of New England) Minnesota Water Resources Conference October 15, 2013

http://stormwater.safl.umn.edu/

Project Team and Partners

This study was funded through a grant from the National Oceanic Atmospheric Administration SARP program.



Stormwater & Climate Change: framework for adaptation planning and

implementation

• Vulnerability assessment – Climate model…how is rainfall distribution projected to change?

– Stormwater / Urban drainage model…is capacity of

existing SW infrastructure adequate?

• Assessing adaptation alternatives

• Outreach & community planning


Recent Climate Trends

Occurrence of heavy precipitation events (largest 1% of all events) has increased 31% across the Great Lakes Region.

Updated from Groisman et al., 2005 Stockton, MN - FEMA


Anticipated Impacts Due to Changing Climate

Carmen et. al, 2012

Despite recognition of negative climate-related impacts to stormwater management, few communities have

implemented adaptation measures


Study Goal Provide adaptation

framework for local communities to address changes in precipitation patterns and land use to reduce: 1. the risk of flooding 2. impacts to stormwater

infrastructure and downstream water resources

Duluth, MN 2012 - MN Sea Grant


Objectives

1. Identify the vulnerability of local stormwater infrastructure and downstream water resources to changes in precipitation and land use.

2. Identify local and specific adaptation options, including costs.

3. Engage stakeholders to identify strategies that promote community adaptation and inform local decision-makers.

Minnehaha Creek Watershed

Minneapolis

Urban Case study: Lake Hiawatha watershed (S. Minneapolis)

1100 ac Pipeshed •50% impervious •3 detention basins •20 miles of pipes

Pipeshed outlet at Lake Hiawatha


Rural Case study: City of Victoria 1145 ac Watershed

•31 Stormwater ponds •8 natural lakes & wetlands •12 miles pipes; 3 miles open channel


Victoria: Climate AND

Land Use Changes

Red shading denotes areas of future development

Existing: 14% impervious Projected buildout: 29% impervious

Study watershed outlet

Run-off / Peak Flow Calculations

EPA-SWMM

Methods

HYDROLOGIC CHARACTERISTICS - Impervious Area - Green-Ampt Infiltration - Area, Slope, Flow Length

HYDRAULIC NETWORK 1. Existing 2. Adaption to Climate- changed scenarios

PRECIPITATION 1. Historic climactic data 2. Climate-changed Scenarios - Global Circulation Models - Down-Scaling

DATA Input

SYSTEM COMPONENT ADEQUACY - Current Design Storm - Climate Δ Projections

EFFICACY OF ADAPTATION OPTIONS - Pipe upsizing - Underground storage - LID

PROJECTED COSTS… - of predicted flooding - to implement adaptation options

Outputs

1


1. Vulnerability assessment: climate projections

Global climate models: GFDL CM2.1, CM3.0, PCM, CCSM4

Emission scenarios: A1b, Aifi, rcp45, rcp60, rcp85

Statistical downscaling by: 1. modified Delta 2. Empirical method

Return period (years)

Current 10-YR design Storm

(TP40)

mid-21st cent. Optimistic

(A1b)

mid-21st cent. Moderate

(A1fi)

mid-21st cent. Pessimistic

(A1fi, upper 95th C.I.)

2.5 2.8 2.84 3.3 6.86

5 3.6 3.47 4.11 8.4

7.5 3.8 3.88 4.66 9.39

10 4.1 4.19 5.1 10.13

25 4.8 5.28 6.74 12.75

50 5.4 6.22 8.31 15.03

75 5.7 6.82 9.39 16.5

100 6.0 7.27 10.23 17.59

Climate modeling results: Current and Future

2% 24% 147%

SWMM Precipitation Inputs

Atlas 14 10YR, 24hr: 4.24 in (3.73-4.85 in)

2. Vulnerability assessment: H&H Modeling (EPA SWMM)

Lake Hiawatha SWMM parameters Victoria

50% % Impervious 14%; 29%

0.25 Ksat (in/hr) 0.14

59 Surface storage volume (MG) 1826

mid-21st Century “pessimistic”

mid-21st Century “moderate”

mid-21st Century “optimistic” Recent climate

Vulnerability Assessment

System Adequacy under climate change: urban case

Moderate emissions scenario

Optimistic emissions scenario

Pessimistic emissions scenario

System Adequacy: Flooding, Urban case


05

1015202530354045

0% 50% 100% 150%

Floo

d Vo

lum

e (M

G)

% Increase over Current 10-yr Design

Total Flood Volume

Street Storage

Over-curb Flooding

System Adequacy: Current 10-yr storm (4 in)


System Adequacy: “Moderate” mid-century 10-yr storm (6.5 in)


System Adequacy: “Pessimistic” mid-century 10-yr storm (10.1 in)


SWMM to model Adaptation Options

Infiltrate/LID

Do Nothing

Underground Storage

Upsize Infrastructure

0.01

0.10

1.00

10.00

100.00

3 5 7 9 11

Floo

d Vo

lum

e (M

G)

Precip Depth (inches)

Existing Pipe Up-sizing 10% LID 15% LID

20% LID 25% LID 100% LID

Adaptation scenarios: flooding impacts in Lake Hiawatha study site

Moderate Optimistic Pessimistic


Precip depth Qpeak pipe replacement (ft)

Underground Storage (ac-ft) (inches) ( cfs ac-1)

4.15 2.0 3439 0

4.77 2.4 5740 0

5.66 3.0 12272 0

6.56 3.6 20405 13.0

8.07 4.6 20405 30.6

10.1 6.0 20405 61.5

Adaptation Options

Costs of Adaptation, Urban case: Extent of pipe upsizing & underground storage to

maintain current level of service


Costs of Adaptation, Urban case: Pipe upsizing & Underground storage to maintain LOS

Adaptation Options

Costs from City of MInneapolis

$0

$20,000,000

$40,000,000

$60,000,000

$80,000,000

$100,000,000

$120,000,000

$140,000,000

0% 25% 50% 75% 100% 125% 150% 175%% Increase over current 10-YR storm



$0

$20,000,000

$40,000,000

$60,000,000

$80,000,000

$100,000,000

$120,000,000

$140,000,000

0% 25% 50% 75% 100% 125% 150% 175%% increase over current 10-YR storm

Costs of Adaptation, Urban case: Pipe upsizing & Underground Storage

w/ Increased Infiltration

Adaptation Options

Infiltration costs from Erickson et al., 2007


• Differences from Lake Hiawatha Pipeshed… – Climate change + land use

change – More reliant upon surface

conveyance and storage (stormwater ponds, wetland buffers, lakes)

Vulnerability: contrasting Lake Hiawatha and Victoria


Vulnerability: contrasting Lake Hiawatha and Victoria

Victoria

Lake Hiawatha


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3.93 4.15 4.77 5.66 6.56 8.07 10.1

Tota

l Flo

od V

olum

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illio

n ga

llons

)

Precip Depth (in)

Existing L/U Build-Out

Flooding impacts: climate + landuse change



Victoria System

Adequacy: Current 10-yr storm (4 in)


Victoria System

Adequacy: “Moderate” mid-

century 10-yr storm (6.5 in)


System Adequacy:

“Pessimistic” mid-century 10-yr storm

(10.1 in)


COMMUNITY ENGAGEMENT National Climate Assessment, 2013


Why involve the public?

1.Improve quality of work 2.Improve legitimacy 3.Improve capacity of

environmental assessment & decisions


Stakeholder Engagement Process

• Study Newsletter/Website • Forums (2) • Adaptation Work Groups (4) • Community Meetings (3-4) • Regional Symposium • Advisory Committee • Study Evaluation

Municipal Officials City Staff Regional Agencies State agencies Federal Agencies Non-Profits Homeowner Assoc. Lake Associations Academia Builders Developers Landowners Insurance Utilities


Take Home Points • Projected climate changes present significant

challenges, esp. built-out environments – Need to consider downstream impacts of pipe

upsizing – Need to incorporate non-stationarity of climate in new

construction and retrofits

• Best bet in building resilience in climate uncertainty: Conservation development policies that retain hydrologic ecosystem services!!


Thank you!

Additional information can be found at:

www.minnehahacreek.org/WET



The frequency of intense storms in our region has increased, and climate projections indicate that trend will continue.

The capacity of existing stormwater infrastructure may be inadequate in our communities, resulting in more frequent

flooding and impacts to infrastructure, public safety, and the quality of downstream water bodies. Development and

redevelopment can exacerbate the problem, but also provide an opportunity for communities to make sound planning

decisions that reflect adaptation to our new environment. A two-year study within the Minnehaha Creek watershed

focused on community stormwater adaptation in two cities, the urban City of Minneapolis and the suburban

community of Victoria. Results of this study provide a framework for community adaptation planning, including risk

and vulnerability assessments, planning and implementation strategies, and a stakeholder engagement process that

increases the capacity of a community to respond to a changing environment.


Options for local-scale design targets: • Downscale: - Contract out for it - via universities with climate change research programs - In-house via NARCCAP and in-house IT/stat guru (1/8° resolution) • Don’t downscale: - Use national/regional reports, research articles - Historical 200/250-year (100-year is better than nothing) Chart: Return period x precip - Bottom-up (no downscaling)

http://stormwater.safl.umn.edu/ 11/8/2013 46 Minnehaha Creek Watershed

10-yr Event

Flood Volume

Increase Undersized Pipes Reduce Street Flooding Create Flood Storage

MG Ft of Pipe

After pipe upsizing

(MG) Cost

Excess Street (MG) Cost

3.9” 0.07 0 0% $0 0 $0

6.6” 1.6 4,199 -75% $205,000 0.91 $150,000-$575,000

10.1” 16.9 14,132 -30% $775,000 7.47 $1,015,000-$2,350,000

Options for Adaptation - Victoria

*LID does not provide effective flood control during large storm events

Precip depth Qp

pipe replacement low high

(inches) ( cfs/ac) (feet) cost cost

4.15 2.04 3439 $ 3,994,155 $ 9,083,822

4.77 2.44 5740 $ 6,666,603 $ 15,161,715

5.66 3.02 12272 $ 14,253,058 $ 32,415,430

6.56 3.63 20405 $ 23,698,961 $ 53,898,048

Hiawatha : (Preliminary) Cost Estimates

for Up-sizing Pipes

Excess Vol.

Flooding w/ pipe Estimated # of projects

Precipitation Volumes upsizing Excess Vol. Underground Basin comparable

(Mgal) (Mgal) acre-feet Costs to 37th ave

6.56 10.1 4.2 13.0 $ 9,833,167 4

8.07 20.0 10.0 30.6 $ 23,149,155 9

10.1 40.1 20.0 61.5 $ 46,502,636 18

Hiawatha : Underground Storage Cost Estimates for

Post-Piping Upgrade Volumes (preliminary)

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