mapping sfhas using 2d modeling - amazon s3 · 2019. 4. 24. · aka – the deckless bridge 3....

Mapping SFHAs Using 2D Modeling

Cooperating Technical Partners Information Exchange

ASFPM Flood Science Center April 24, 2019

Audio and Web Settings

Open and hide your control panel using the orange arrow button at top left corner• Choose “Computer audio” to use

computer speakers or headphones• Choose “Phone call” to dial in using

the information provided

Submit questions & comments via the Questions panel

Participation

Webinar Logistics

• All lines will be automatically be muted.

• Use the Question window in the control panel to submit your question or comment to the Flood Science Center Organizer.

• Select questions will be read to the presenter and answered.

• Questions not asked during the webinar will be answered and posted to the CTP Webinar page.

• Certified Floodplain Managers are eligible for 1 Continuing Education Credit for participating in this webinar.

• You must have registered individually and indicated you are a CFM at time of registration.

• Eligibility for CEC is dependent on your participation in poll questions and time spent viewing the webinar, as determined by the webinar software.

• Attending this webinar in a group setting or only viewing the recording is NOT eligible for CEC.

Continuing Education Credits

• To suggest future CTP webinar topics, please contact Alan Lulloff at [email protected] or type a suggested topic into the Questions panel today.

• ASFPM CFM CECs will be automatically applied.

• Certificates of Attendance will be emailed, please contact [email protected] with any certificate issues.

• Follow-up email with link to slides and recording will be sent next week

Thank You for Joining Us!

Additional Logistics

mailto:[email protected]


Sunday, May 19, 2019

1:00 - 5:00 pm: Cooperating Technical Partners Boot Camp: Improving Resilience

• Training Workshop: $45, 3.5 CECs (Registration Required)

• Instructors: Laura Algeo, PE, Necolle Maccherone, CFM, and Marc Pearson, GISP, CFM

• This workshop is modelled after the CTP Special Topics Course at the Emergency Management Institute (EMI), a four-day course which provides students with a deeper understanding of the CTP Program and how it operates. This workshop is a great overview of the CTP Program for students who cannot attend EMI. Attendees will come away with a broad knowledge of the CTP Program and specifics about some of the CTP Program’s key objectives which drive towards increasing awareness, mitigation investments and resilience at the local level.

CTP Events at the 2019 ASFPM National

Conference in Cleveland

Monday, May 20, 2019

3:00 - 5:00 pm: CTP Conversation

• CTP Subcommittee Meeting – Room 24

7:00 - 9:00 pm: Off-site Cooperating Technical Partners Social

• Corner Alley402 Euclid AvenueCleveland, OH 44114



Tuesday, May 21, 2019

1:45 - 3:15 pm: Concurrent Session B4: CTP Showcase

• Flood Risk CHAMPions

• Leveraging Technical Assistance to Enhance Local Awareness and Mitigation Through Risk MAP

• Lessons from the Field, CTP Program Project Management Best Practices


Conference in ClevelandLink to more CTP events found at:

no.floods.org/CTP2D

https://no.floods.org/CTP2D

ASFPM Mapping and Engineering Standards Committee

Cooperating Technical Partners Sub-committee

Co-chairs: • Thuy Patton, CFM

Colorado Water Conservation Board• Carey Johnson

Kentucky Department for Environmental Protection

Goals:• Identify common concerns• Provide opportunities for information exchange• Identify training needs• Promote and document the value of CTPs

Agenda

• Introduction - Alan Lulloff, ASFPM Flood Science Center

• Description of pilot project - Carey Johnson, KY DEP

• Introduction to 2D modeling - Davis Murphy, AECOM

• Pilot project 2D modeling approach and results - Davis Murphy, AECOM

• Floodplain mapping with 2D model results from HEC-RAS - Ben Conley, AECOM

• Questions/Discussion

>

Davis Murphy, PE, CFMBen Conley, GISP, CFM

Mapping SFHAs Using HEC-RAS 2D Rain-on-Mesh Modeling

Carey JohnsonProgram DirectorKentucky Division of Water

Today’s Topics

1. About KDOW

2. Overview of Pilot Projects

3. 2D Rain-on-Mesh HEC-RAS Modeling Approach

4. Floodplain Mapping with 2D Rain-on-Mesh HEC-RAS Model Results

5. Questions/Discussion

Kentucky Division of Water

Mission• To manage, protect and enhance the quality of the Commonwealth’s

water resources.

Primary Responsibilities

• Safe Drinking Water Act• Clean Water Act

• Floodplain Management• FEMA Cooperating Technical

Partner (CTP)• Dam Safety

2D Pilot Areas

Highland Pigeon Watershed – Regulatory Studies(New A and AE Zone SFHAs)• USGS gage at Beaverdam Creek used for calibration• 388.6 mi2 watershed• Full LiDAR coverage

Highland Pigeon Watershed

Beaverdam Study Area

2D Pilot Areas

Tradewater River Watershed – BLE Study• Western KY, just southwest of Highland-Pigeon• 941.5 mi2 watershed• Multiple USGS Gages along Tradewater

River and tributaries• Full LiDAR coverage

Hydrologic Study Methods

Statistical MethodsGage Analysis/Bulletin 17C

Regression Equations

Rainfall-Runoff ModelingHEC-HMS

HEC-RAS 2D

Hydrology and Flood Insurance Studies

• Zone A Studies:• Typically use USGS peak flow regression equations

• Regression equations have some drawbacks:• Not highly localized• 68% CIs ranging from -36% to +57% of peak flow• Peak flow estimates instead of the full hydrograph

• No estimates of volume• No unsteady state modeling

Rainfall-Runoff Model Advantages

Design Storm VariabilityAllows for modeling of any storm event with various rainfall temporal distributions, durations, and intensities. Move to MitigationRainfall-runoff models allow for Benefit-Cost Analyses for detention and retention mitigation alternatives.Outreach OpportunitiesMore detailed model results. Ability to connect various models together for real-time events and forecasting, replicate past events or other “what-ifs”, and provide hydrologic models for local stakeholder use in planning and development.

HEC-RAS Watershed Modeling

HEC-RAS 5o Two-dimensional hydraulic model

oAssign hyetograph/effective rainfall depths as a boundary conditiono Does not compute rainfall abstractions at this time (e.g. TR-55 Curve

Number calculations)

oNovel flexible mesh schemeo Terrain resolution captured in detail, even with large mesh elements.

Poll Question

What is your experience with 2D models and their outputs/products?

> This webinar is my first time learning about 2D modeling

> I have heard of others using 2D models for floodplain mapping

> I have interacted with 2D models or their final products

> I work with 2D models or use them to create floodplain maps

The Case for HEC-RAS 2D

Pros:o Familiar modeling interfaceo Free to useo Large user baseoCombines hydrology and hydraulicsoHydrologic routing is baked into the modeloAs inexpensive as USGS Reg. Eq.’s + 1D steady-state models oAs accurate or better compared to 1D steady-state modelso Increases credibility through highly compelling graphics for

outreach and communication with local stakeholders.

Cons:oNew software capabilities; learning curve for users and

stakeholders

USGS gage

>50% of the flow is expected to bypass the gage for the 1% annual chance flood

HEC-RAS 2D Rain-on-Mesh Approach

• Create simple HEC-HMS model• Passes effective rainfall distributions to HEC-RAS via DSS files• Only need two inputs:

• Composite Curve Number• Design event rainfall depth• NOTE: Computation time step = 1hr

• Import LiDAR DEM using RASMapper• Create 2D model domain extents covering the entire

watershed of interest• Import a watershed polygon from GIS• OR manually draw the domain extents

2D Domain

LiDAR Terrain

Beaverdam Creek


• Additional HEC-RAS inputs:• Roughness (Manning’s n values)• Land Cover datasets and user-defined override regions• Outlet boundary conditions• Normal Depth Slope, Rating Curve, Known WSEL, etc.

• 2D considerations• Breaklines for additional detail where needed• Mesh cell size• Time step

Mesh elements

Breakline: Road crown

Breakline: Channel berms

Mesh cell faces

2D Domain

Manning’s n viaLand Cover Data

User-defined roughness zone


Model Calibration Tools

• Curve Number• Adjusts rainfall depth at all time steps, and therefore

directly adjusts volume.

• Manning’s n• Locally adjust hydraulics when a rating curve is available• Adjust watershed and subbasin timing, and therefore peak flows

HEC-RAS 2D – Rain on MeshSingle VS Multiple Basins

Single Watershed VS

Pros:• Fully continuous model/No

smoothed “connections”

Cons:• Longer run times• Less flexible for future

refinement• Difficult to work with using an

average workstation

Multiple Watersheds

Pros:• Shorter run times• More flexible for future

refinement• Easy to work with using an

average workstation

Cons:• Disconnected

subwatersheds/smoothed “connections”

HEC-RAS 2D – Rain on MeshSingle VS Multiple Basins

HEC-RAS 2D – Rain on MeshShared Boundary Adjustments

HEC-RAS Watershed ModelingTerrain Adjustments

HEC-RAS Watershed ModelingTerrain Adjustments

350

352

354

356

358

360

362

364

48000 50000 52000 54000 56000 58000 60000 62000 64000

Elev

atio

n in

feet

(NAV

D88)

Stationing Upstream of Confluence with Ohio River

LiDAR Invert Profile

Interp. Survey Profile

Adj. Invert Profile

HEC-RAS Watershed ModelingStructures

1. Breaklining

2. Modify terrain to match structure opening geometryAKA – The deckless bridge

3. Internal SA/2D Area Connections

1. Rating Curve

2. Model as a Culvert

HEC-RAS Watershed ModelingStructures

HEC-RAS Watershed ModelingPlan Setup

Equation Sets: Diffusion Wave -VS- Full Momentum

HEC-RAS Watershed ModelingPlan Setup

• Initial Conditions• Improves model stability at start of simulation• Several hours with precipitation boundary condition

• Courant ConditionsDiffusion Wave Full Momentum

HEC-RAS Watershed Modeling2D Flow Area Tolerance Settings

DEFAULT SETTINGS ADJUSTED VALUES

HEC-RAS Watershed ModelingIncorporating Beaverdam Creek Mini Pilot Area

HEC-RAS Watershed ModelingBoundary Conditions

Initial Run

U/SQ Max = 8,660 cfsWSE Max = 378.1’

D/SQ Max = 8,660 cfsWSE Max = 381.0’

HEC-RAS Watershed ModelingBoundary Conditions

Initial Run Final Run





What are some of the benefits of 2D Rain-on-Mesh modeling?

> Combines Hydrology and Hydraulics in one model

> Allows for simulation of various rainfall events

> Capable of modeling multiple unique flow paths

> Accounts for flood water volumes

> All of the above

Poll Question

HEC-RAS Watershed ModelingRender Modes

Sloping Render Mode

Horizontal Render Mode

HEC-RAS Watershed ModelingWSE Output

• Horizontal Render Mode

• Set depth tolerance to large negative number(e.g. -1000 ft)

• Export WSE (Max) raster

• Export mesh cell center points

• Assign WSEs (or terrain elevations) to cell centers in GIS

Floodplain Mapping – Why Post Processing?

• 2D models output a 1% annual chance floodplain boundary, why not use it?

• Floodplain extents are watershed wide and not limited to specific study streams

• Not limited to project scope

• Includes every stream, ditch, and swale in watershed

• Beyond regulatory goals (< 1 sq mi drainage area)

Mapping

Backwater elevations associated with receiving

stream elevation

Limit of Study at 1 square mile drainage

Effective 1D Modeling Floodplain

Effective Floodplain and 2D Maximum Water Surface Boundary

2D Maximum Water Surface Boundary with Elevation Isolines

Floodplain Mapping – Process

2D model outputCell centroid points exported to GIS and assigned elevations to create a water surface raster dataset


Create water surface isolines from the water surface elevation grid

• Density needs to be appropriate to recreate the water surface accurately

• Select isolines that intersect the study stream centerline


Filter water surface isolines to recreate the water surface

• Density = 0.1’ interval

• Filter Tolerance = 0.25’ acceptable variance between modeled profile and recreated profile


Recreate water surface from selected lines and intersect with LiDAR terrain for new floodplain boundary.

HEC-RAS Watershed ModelingSome Thoughts on FEMA Deliverables

• Hydrology and Hydraulics delivered together

• No XSs per se, but WSE isolines fulfill similar role• Useful to report WSELs at shared domain boundaries and redelin tie-ins

• Limited reporting needed for discharge estimates• Unlimited hydrograph data can be obtained in the model• Provide discharges at areas of interest:

• 2D domain outlets• Significant roadways and confluences for AE studies• Etc.

• Profile Baseline still useful• Not needed in order to run the model

(unlike 1D HEC-RAS)• Valuable for QC of the terrain model

Questions&

DiscussionAlan Lulloff, PE, [email protected]

Carey Johnson, [email protected]

Davis Murphy, PE, [email protected]

Ben Conley, [email protected]

ASFPM Flood Science Center

Cooperating Technical Partners

Information Exchange





Poll Question

Please rate this webinar.

Sunday, May 19, 2019

1:00 - 5:00 pm: Cooperating Technical Partners Boot Camp: Improving Resilience

• Training Workshop: $45, 3.5 CECs (Registration Required)

• Instructors: Laura Algeo, PE, Necolle Maccherone, CFM, and Marc Pearson, GISP, CFM

• This workshop is modelled after the CTP Special Topics Course at the Emergency Management Institute (EMI), a four-day course which provides students with a deeper understanding of the CTP Program and how it operates. This workshop is a great overview of the CTP Program for students who cannot attend EMI. Attendees will come away with a broad knowledge of the CTP Program and specifics about some of the CTP Program’s key objectives which drive towards increasing awareness, mitigation investments and resilience at the local level.



Monday, May 20, 2019

3:00 - 5:00 pm: CTP Conversation

• CTP Subcommittee Meeting – Room 24

7:00 - 9:00 pm: Off-site Cooperating Technical Partners Social

• Corner Alley402 Euclid AvenueCleveland, OH 44114



Tuesday, May 21, 2019

1:45 - 3:15 pm: Concurrent Session B4: CTP Showcase

• Flood Risk CHAMPions

• Leveraging Technical Assistance to Enhance Local Awareness and Mitigation Through Risk MAP

• Lessons from the Field, CTP Program Project Management Best Practices


Conference in ClevelandLink to more CTP events found at:

no.floods.org/CTP2D

https://no.floods.org/CTP2D

• Certified Floodplain Managers are eligible for 1 Continuing Education Credit for participating in this webinar.

• You must have registered individually and indicated you are a CFM at time of registration.

• Eligibility for CEC is dependent on your participation in poll questions and time spent viewing the webinar, as determined by the webinar software.

• Attending this webinar in a group setting or only viewing the recording is NOT eligible for CEC.

Continuing Education Credits

• To suggest future CTP webinar topics, please contact Alan Lulloff at [email protected] or type a suggested topic into the Questions panel today

• ASFPM CFM CECs will be automatically applied

• Certificates of Attendance will be emailed, please contact [email protected] with any certificate issues

• Follow-up email with link to slides and recording will be sent next week

Thank You for Joining Us!

Closing Comments



mapping sfhas using 2d modeling - amazon s3 · 2019. 4. 24. · aka – the deckless bridge 3....

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