Integrated HEC-RAS 2D Models for the Sacramento River Basin Floodplains and Bypass SystemsPresented by: Chakri Malakpet, PE, CFM, CH2M

Co-Authors:Yiguo Liang, PE, PhD, DWRRajmani Subedi, PE, PH, CFM, GISP, DWRRicky Doung, DWRMary Horvath, PE, CFM, CH2MPaul Robinson, CH2M

September 09th, 2016

Presentation Overview• DWR’s Initiative to develop Improved

H&H Tools• 2D Model Coverage• Potential Applications of the 2D Models• Challenges Faced and Lessons Learned

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DWR’s Initiative to Develop Improved H&H Tools

• To improve flood risk and ecosystem management in California Central Valley

• Supports major flood management efforts

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2D Model Coverage

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2D Model Elements

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Terrain DataCVFED LiDAR (3.125’ cell size)CVFED Channel Bathymetry

Land Use DataNLCD 2011 (30m cell size)

2D MeshUrban Areas = 200’ avg cell size

Non‐Urban Aeas = 400’ avg cell sizeBreak Lines (features > 3’ above ground)

Floodplain StructuresUnderpasses and Stream Crossings

Based on As‐built Drawings & Field Surveys

Inundation OutputsFlood Depth, WSE, Velocity, Arrival Time, Depth*Velocity, Recession, 

Duration, Streampower etc

Additional Data Sources

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Yuba River ChannelBathymetry (YCWA)

Tule Canal and KLRC Bathymetry (CBEC)

Fremont Weir Bathymetry (DWR NRO)

Liberty Island  Bathymetry (EDS)

USGS DEM

CVFED Channel Bathymetry

Potential Model Applications• Flood Risk Management Analyses• Emergency Response Planning• Coupled Flood Forecasting• Ecosystem Management Analyses

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Flood Risk Management Analyses• Scalable from

region to system level

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Flood Risk Management Analyses

• Scalable from region to system level

• Levee breach analysis to estimate flood damages

• Regional flood mitigation project design evaluation

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Emergency Response Planning

• Flood hazard and Zoning Maps for FEMA NFIP

• Flood emergency evacuation route planning

• Flood emergency response actions analyses

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Arrival Time Map

Velocity Map

Coupled Flood Forecasting

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45ºN

35ºN

25ºN

170ºE140ºE 160ºW 130ºW 100ºW

1 2 3 4 5 6 7

Temperature

Precipitation

Weather Forecasting

Watershed 

Flood Forecasting

Streamflow

Ecosystem Management Analyses

• Ecosystem restoration impacts on flood elevations

• Weir modification impacts on bypass inundation

• Fish habitat suitability based on inundation depth, velocity and duration

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Sacramento Weir

Fremont Weir

Modeling Challenges Faced• 2D Mesh Development• Modeling bridges in 2D areas• Hydraulic structure instabilities• 1D-2D Connections• Geo-referencing lateral structures

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False Inundation due to Cell Leakage

2D Mesh Development• Extensive Break

Lines Required• Manual Adjustment

of 2D mesh is needed near break line intersections

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Bridge pier width and spacing used to modify weir embankment profile

Bridges in 2D Areas• No bridge modeling

routines in 2D areas• Bridges represented

by modifying weir profiles

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Variable max velocity due to bridge piers

• Oscillations of flow through the culverts

• 2D mesh refined to contain HW and TW cells within high ground

• Culvert invert raised slightly

Hydraulic Structure Instabilities

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1D-2D Connections• Initial conditions of

1D and 2D elements are critical

• Computational interval needs to satisfy recommended courant number

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2D Area on the downstream end

2D Area on the upstream end

Geo-referencing Lateral Structures

• HW stations are computed correctly when XS cutlinesend points are close to LS alignment

• LSs need to start and end at XSs

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Trim XS cutlines to lateral structure lines

Questions?

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