BUILDING STRONG® 2D Modeling and Mapping with HEC-RAS 5.0

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US Army Corps of EngineersBUILDING STRONG®

2D Modeling and Mapping with HEC-RAS 5.0

Gary Brunner, P.E., D.WRE, M.ASCE

Mark JensenSteven PiperCameron AckermanAlex KennedyBen Chacon, Ph.D, RMA

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Overview

HEC-RAS Mapper

2D Flow Modeling Capabilities/Features

Example 2D Modeling Applications

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RAS Mapper

RAS Mapper is completely new for version 5.0 Goals:

►Visualization of results►Improve the efficiency of hydraulic modeling►Utilize and focus modelers skill using RAS►Reduce the dependency of GIS skills

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RAS Mapper

Data LayersWindow

DisplayWindow

Status Window

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RAS Mapper Terrain Single or multiple terrain model support Flexible tile arrangements Different data resolutions per tile ok! No intended terrain file size limitations

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TIN Stitches Covers transitions across datasets Fills in holes in terrain data

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Example Terrain Layer Columbia River

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Channel Data

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Channel Data

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Adding Channel Data

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Adding Channel Data

New Terrain Priority – Channel data highest priority

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Terrain with Channel

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Terrain Visualization

Color Ramp Contours Hillshade

Additional options

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Hill Shading

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Contour Plotting

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Land Cover Data Support use of Land Cover data for

estimating Manning’s n values►Raster and Shapefile polygon datasets

NLCD 2011► http://www.mrlc.gov/nlcd2011.php (30-m raster)

USGS LULC ► http://water.usgs.gov/GIS/dsdl/ds240/index.html (vector)► http://edcftp.cr.usgs.gov/pub/data/landcover/states/ (30-m raster)

Additional Resources-http://landcover.usgs.gov/landcoverdata.php

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Imperfect Data

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2D Area Manning’s n Regions

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Manning’s n by Land Cover

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RAS-Mapper Results Mapping Dynamic Mapping - Animation

►On-the-fly mapping – you don’t have to wait for inundation map to be processed!

Stored Maps – Depth Grid written to a file.

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Dynamic Mapping

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Adding a New Results Map Layer Depth, Elevation, Flow, Velocity, Shear Stress Inundation Boundary Arrival Time, Duration, Percent Time Inundated,

Recession, (at a certain depth) Hazards (depth*velocity and depth*V2)

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Creating Static (Stored) Maps Tools – Manage Results Maps

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Results Layer Properties

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Querying RAS Mapper Results

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Profile Lines

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Time of Arrival

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RAS Mapper – Background Imagery

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RAS Mapper - NLD

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Export RAS Tiles for Web Mapping

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Display Results in Web Browser

Write out Depth Grid to a Tile Cache Place Tile Cache on a Server Text or email people the URL to the Tile

Cache Example:http://www.hec.usace.army.mil/Maps/demo/modesto-dev

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2D Unsteady Flow Modeling Directly Inside HEC-RAS

Why: Need a fast and robust 1D/2D Unsteady Flow Solution for Flood Risk

Management Type Analyses (Monte Carlo), Dam and Levee breaching Improved hydrodynamic modeling for complex river/floodplain situations

What: 2D Flow Areas are analogous to HEC-RAS Storage Areas

Multiple 2D Flow Areas in a single run Flexible Connections to 1D model elements

Directly Time Step by Time Step Coupled 1D/2D Computations inside of HEC-RAS Unsteady Flow Engine More Accurate overbank flow water surfaces and flow paths Faster than separate 1D and 2D programs combined

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HEC-RAS Two Dimensional Flow Modeling Advantages/Capabilities

1. The ability to perform 1D, 2D only, or Combined 1D and 2D modeling 2. The 2D equation solver uses an Implicit Finite Volume algorithm.3. Can solve either 2D Diffusion Wave or 2D Full Saint Venant Eqns. 4. The 1D and 2D solution algorithms are tightly coupled on a time step

by time step basis (or even iteration by iteration).5. The software was designed to use Unstructured or Structured

Computational Meshes. The outer boundary of the computational mesh is defined with a multi-point polygon.

6. The underlying terrain and the computational mesh are pre-processed in order to develop detailed Hydraulic Property Tables for the Cells and the Cell Faces.

7. Mapping of the combined 1D/2D inundation area, and animations of the flooding can be done right inside of RAS, using RAS-Mapper.

8. The 2D flow computations take advantage of Multi-processors 9. 64 Bit and 32 Bit Computational Engines.

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2D Hydraulics Mass Conservation (Continuity) Full Momentum Conservation (Shallow Water Eqns.)

Gravity and Friction Hydrostatic pressure Acceleration (local and convective) Turbulent eddy viscosity (optional) Coriolis term (optional)

Diffusion Wave Equation Gravity and Friction Hydrostatic pressure

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Full Momentum vs. Diffusion Wave Example uses for Full Momentum:

► Flows with dynamic changes in acceleration (Rapid rise and fall)► Locations with abrupt spatial contractions and expansions with high velocity

changes► Waves bouncing off walls and objects, etc…► Detail solution of flows around obstacles, bridge piers and abutments► Detailed mixed flow regime: sub to supercritical flow transitions, and hydraulic

jumps (Super to subcritical)► Tidal boundary conditions (wave propagation upstream)► Super Elevation around Bends

Example uses for Diffusion Wave:► Flow is mainly driven by gravity and friction► Fluid acceleration is monotonic and smooth, no waves► To compute rough global estimates such as flood extent► To assess interior areas due to levee breaches► For quick estimations before a full momentum run

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Instantaneous Dam/Levee Breach

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Instantaneous Dam/Levee Breach Velocity (m/s) Animation

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Unstructured/Flexible Computational Mesh

Irregular polygon outer boundary Grid can be unstructured (irregular) or structured

(rectangles), or mixed Computational cells can vary in shape or size. Cells can

have any number of sides (HEC-RAS: up to 8 sides) Cells must be concave HEC-RAS can handle orthogonal and non-orthogonal

grids, but orthogonality simplifies formulation and reduces compute time. (Grid orthogonality is where the centers of two adjacent cells are perpendicular to the face between them)

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HEC-RAS 2D Flow Area Example Flexible Computational Mesh

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Break Lines for Channel Banks

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Cell and Face Pre-Processing Each cell, and cell face, of the computational mesh is pre-

processed in order to develop detailed hydraulic property tables based on the underlying terrain used in the modeling process.

The 2D Mesh pre-processor computes a detailed elevation-volume relationship for each cell.

Each face of a computational cell is pre-processed into detailed hydraulic property tables (elevation versus, wetted perimeter, area, roughness, etc…).

Computational cells can be partially wet. This allows the user to use larger computational cells, without

losing too much of the details of the underlying terrain. The net effect is that larger cells means less computations, which

means much faster run times. Additionally, HEC-RAS will produce more detailed results for a

given cell size than other models that use a single elevation for each cell and face.

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Computational Mesh with Detailed Sub-grid Terrain Data - Continued

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Computational Cells are Pre-ProcessedElevation vs. Volume

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Computational Faces are Pre-ProcessedElevation vs. Area, Wetted Perimeter, and n

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Benefits of using the detailed sub-terrain for the cell and face hydraulic properties

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Benefits of Combined 1D/2D Solution Algorithm

Can model larger systems►1D modeling where appropriate►2D modeling where it is needed►Ex. 1D River system – 2D Areas behind

levees Faster Computational Speed More accurate flow transfers between 1D

and 2D elements46

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New Madrid Floodway

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Current limitations of the 2D modeling capabilities in HEC-RAS 5.0

More flexibility for adding internal hydraulic structures inside of a 2D flow area (culverts/gates)

Cannot currently perform sediment transport erosion/deposition in 2D flow areas.

Cannot current perform water quality modeling in 2D flow areas.

Cannot connect Pump stations to 2D flow area cells. Cannot use the HEC-RAS bridge modeling capabilities inside

of a 2D flow area. You can do culverts, weirs, and breaching by using the SA/2D Area Conn tool.

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Development of a 2D Unsteady Flow Model with HEC-RAS

Development of the 2D Computational Mesh: Develop a Terrain model and background imagery in RAS

Mapper. These can now be used in the RAS geometry editor. Draw a Polygon for the Boundary of the 2D Area Add any break lines needed for levees, roads, and high ground

barriers Enter a nominal cell size to Create the 2D Computational Mesh Edit/Modify the Computational Mesh as needed Run the 2D Geometric Pre-Processor

Connecting 2D Flow Area(s) to 1D Hydraulic Elements Enter Boundary and Initial Conditions Data Run the combined 1D/2D Unsteady-Flow Model View combined 1D/2D output with RAS-Mapper

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Create a Terrain Model and Background Map Layers in RAS Mapper

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Turn on Background Maps in Geometry

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Draw a Polygon Boundary for the 2D Area

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Create the 2D Computational Mesh

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Example Generated Mesh

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Adding Break Lines

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Connecting 2D Flow Areas to 1D Hydraulic Elements

Laterally to 1D river reaches using a Lateral Structure

Directly to the downstream end or upstream end of a 1D river reach

Directly to another 2D Flow Area or Storage Area using the SA/2D Area Connection.

Multiple 2D Flow Areas in a single model Hydraulic Structures inside a 2D Flow Area

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Connected 1D River to 2D Flow Area with Lateral Structure

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Sacramento River System Model

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Sacramento River System Model

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Natomas, California

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Directly connecting an Upstream River Reach to a Downstream 2D Flow Area

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Directly connecting an Upstream 2D Flow Area to a Downstream River Reach

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Connecting a 2D Flow Area to a Storage Area using a Hydraulic Structure

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SA/2D Hydraulic Connection

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Montecello Dam Breach Example

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Connecting a 2D Flow Area to another 2D Flow Area using a Hydraulic Structure

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Multiple 2D Flow Areas in the one Model

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Hydraulic Structures inside a of a 2D Area

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Hydraulic Structure Computation Options

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Hydraulic Structures inside of a 2D Area

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External 2D Flow Area Boundary Conditions

Flow Hydrograph Stage Hydrograph Normal Depth Rating Curve Precipitation

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2D Flow Area Initial Conditions Dry Single Water Surface Initial Conditions Ramp Up Restart File

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Example Applications Muncie Indiana, Levee Breaching Analysis Detailed Urban Flooding – Grid Resolution Tests Detailed Structure with Piers New Orleans Gated Outfall design Bridge Hydraulics

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Muncie Indiana

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Muncie Indiana – Grid Resolution Evaluation200, 100, 50, and 25 ft Grids

Levee Breach Location

Location 1

Location 2

Location 3

Levee OvertoppingLocation

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Muncie Breach Flow Hydrographs

2400 0600 1200 1800 240002Jan00

400013214 LAT STRUCT

Legend

2D 200FT GRID 15 SEC T

2D 100FT GRID

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Muncie Indiana - Location 1

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Muncie Indiana – Location 2

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Break lines Added

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Location 2 – With Break Lines

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Muncie Indiana – Location 3

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Muncie Lower Levee Overflow

2400 0600 1200 1800 240002Jan00

07300 LAT STRUCT

Legend

2D 100FT GRID

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Muncie – Computational Time24 hr Simulation, 5 -15s Time Steps

Test No Grid Size No. Cells Time Step RAS Diff Wave Time Step RAS Full Eqns.

1 25ft 21719 10 sec 2 min 57s 5 sec 12 min 29s2 50ft 5379 15 sec 43s 6 sec 3 min 3s3 100ft 1323 15 sec 9s 15 sec 17s4 200ft 321 15 sec 4s 15 sec 5s

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Detailed River and Urban Floodplain10 ft cells – with break lines

Equation set = Diffusion Wave Grid Size = 10 ft X 10 ft Time step = 2.0 seconds No. Cells = 231490 Event Duration = 2 days 9 hours Run Time = 12 hours 26 minutes

Buildings left in the terrain on purpose.

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Detailed River and Urban Floodplain50 ft cells– with break lines

Equation set = Diffusion Wave Grid Size = 50 ft X 50 ft Break lines at high ground along

channel Banks, gravel pits, etc… Time step = 4.0 seconds No. Cells = 15050 Event Duration = 2 days 9 hours Run Time = 19 minutes, 51 seconds Buildings left in the terrain

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Detailed River and Urban Floodplain Animation

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Upstream of Weir

4/17/2014 0:00 4/17/2014 12:00 4/18/2014 0:00 4/18/2014 12:00 4/19/2014 0:00 4/19/2014 12:00 4/20/2014 0:00

10 ft Grid

50 ft Grid

Water Surface Elevation (ft)

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Upstream of Split

4/17/2014 0:00 4/17/2014 12:00 4/18/2014 0:00 4/18/2014 12:00 4/19/2014 0:00 4/19/2014 12:00 4/20/2014 0:00

10 ft Grid

50 ft Grid

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Downstream of Bend

4/17/2014 0:00 4/17/2014 12:00 4/18/2014 0:00 4/18/2014 12:00 4/19/2014 0:00 4/19/2014 12:00 4/20/2014 0:00

10 ft Grid

50 ft Grid

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Downstream Outflow (cfs)

4/17/2014 0:00 4/17/2014 12:00 4/18/2014 0:00 4/18/2014 12:00 4/19/2014 0:00 4/19/2014 12:00 4/20/2014 0:00

10 ft Grid

50 ft Grid

Outflow in CFS

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Detailed 2D Flow Area Model of Proposed Structure with Piers in Floodplain

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3D View of Proposed Structure Piers

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Proposed Structure with Piers - Continued

Equations = Diffusion Wave to get hotstart, then Full Saint Venant Grid Size = 2 ft X 2 ft Time step = 0.25 second No. Cells = 454,603 Event Duration = 24 hours Run Time = 6 hours 64 minutes

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Proposed Structure with Piers - Animation

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Plot of Velocity Vectors around PiersFlow Direction and Magnitude

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Velocity Tracking and Colored Grids

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Pump Station with Gate Openings

Equation set = Full Momentum Cell Size = 1 ft X 1 ft Time step = 0.1 seconds Eddie Viscosity Coefficient = 1.0 No. Cells = 104197 Event Duration = 30 minutes Run Time = 50 minute 46 seconds

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Boundary Conditions

Upstream Flow Hydrograph:0 to 12500 cfs over 5 minutes

Downstream Boundaries:Stage Hydrograph = -1.0 feet

Initial Conditions:Flat water surface at -1.0 feet

Upstream Flow Hydrograph

Downstream Stage Hydrograph

Pump Station

11 Gate Openings

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Mesh Details – Gate Openings

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WSE HEC-RAS 2D and Fluent 3D

Water Surface2.30 ft

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Velocity HEC-RAS 2D and Fluent 3D

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Flow and Velocity Comparison

Gate # 1 2 3 4 5 6 7 8 9 10 11

FlowRAS 1034 1135 1164 1154 1149 1120 1131 1148 1122 1466 988

FlowFLUENT 1091 1124 1110 1110 1102 1083 1099 1132 1144 1491 984

Ave.VelocityRAS

9.24 9.91 10.28 10.30 10.63 10.40 10.77 10.80 10.63 10.90 6.72

Ave.VelocityFLUENT

9.70 9.92 9.82 9.90 10.00 10.00 10.35 10.79 10.99 10.25 6.78

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Velocity Animation

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Detailed Bridge Modeling

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Conclusions HEC-RAS can now perform 1D, 2D, or combined 1D and 2D

modeling The 2D capabilities can be used for complex hydraulic

systems. The 2D modeling capabilities can handle subcritical,

supercritical, and mixed flow regimes. Wetting and drying of cells is extremely robust, due to the

implicit finite volume algorithm. The hydraulic property tables allow for a more accurate

representation of the terrain and results in fewer cells being needed to get accurate hydraulic results. Fewer cells equates to less computation time, which will allow users to model larger areas and longer simulation times faster.

BUILDING STRONG® 2D Modeling and Mapping with HEC-RAS 5.0

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