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June 23, 2016
Applications of 2D Surface Flow
Modeling in the new HEC-RAS
Version 5.0
ASFPM Annual National Conference, Gr...
Contents
1. Overview of HEC-RAS prior to 2D capabilities
2. Introduction to 2D Surface Flow Modeling in version 5.0
3. App...
HEC-RAS Overview
3
 Open channel flow freeware published by USACE
 HEC-2 developed in 1966 (FORTRAN), HEC-RAS released i...
HEC-RAS Overview
 Cross sections developed from survey and LiDAR using
HEC-GeoRAS, an extension in ArcMap
4
flowto
HEC-RAS Overview
 Inundation mapping generated from profile interpolated
between cross sections and intersected with terr...
HEC-RAS Overview – Steady State
 1-D Steady Flow – constant discharge
6
2
o f
( /A)Q h+ gA( - S + S )=0
x x
α 
 
Q=VA...
HEC-RAS Overview – Unsteady Flow
 1-D Unsteady Flow – variable discharge and storage
7
 Simulate routed hydrograph, stor...
Representing with 2D Flow with 1D HEC-RAS
8
 Split Flow
Representing with 2D Flow with 1D HEC-RAS
9
 Offline Storage Areas
Introducing HEC-RAS version 5.0!
10
2D Flow Areas in HEC-RAS 5.0
11
 2D Flow Areas can be added to geometry file like Storage Areas
 Digital Terrain Map now...
2D Flow Areas in HEC-RAS 5.0
12
2D Flow Area Calculations
13
 Unstructured Mesh with Implicit Finite Volume solver
 Hydraulic properties of computationa...
2D Flow Area Calculations
14
 Pre-processed stage-storage for each cell
 Cells do not have a “flat bottom” or single dep...
2D Flow Area Calculations
15
 Pre-processed cross section for each cell face from Terrain Map
 Conveyance between cells ...
2D Flow Area Calculations
16
 High resolution Digital Terrain Map
 Lower resolution computational mesh
2D Flow Area Linkages
17
2D Flow Areas can be linked to 1D Flow Reaches
 1D Flow Reaches
 Upstream
 Downstream
 Latera...
Post-Processing - Depth
18
Post-Processing - Depth
19
Post-Processing – Velocity
20
HEC-RAS 2D Riverine Applications
21
Useful for riverine flow outside of well-defined, single channels:
 Inter-connected o...
HEC-RAS 2D Example Application – Dam Breach
22
HEC-RAS 2D Example Application – Dam Breach
23
HEC-RAS 2D Applications – Dam Breach
24
HEC-RAS 2D Applications – Dam Breach
25
HEC-RAS 2D Technical Advantages
26
 Implicit Finite Volume approach
 Improved stability
 Cells can start completely dry...
HEC-RAS 2D Project Advantages
27
 Public Domain
 No license fees
 Large community of practitioners
 Widely accepted as...
CHALLENGES
 Mesh editing tools limited
28
CHALLENGES
 Some limited capacity for modeling structures
 Can represent weirs, levees, and culverts
 Cannot use full 1...
CHALLENGES
 Processing of map inundation, removing “islands”
from high resolution grid; cleaning up “Leaking”
 Can use h...
CHALLENGES
 Limited by quality of LiDAR/Raster…
 Adding bathymetry to LiDAR for “pure” 2D Flow Area runs
31
Thank you.
32
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ASFPM 2016: Applications of 2D Surface flow Modeling in the New HEC-RAS Version 5.0

Derek Etkin presented "Applications of 2D Surface flow Modeling in the New HEC-RAS Version 5.0" at the 2016 Association of State Floodplain Managers conference.

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ASFPM 2016: Applications of 2D Surface flow Modeling in the New HEC-RAS Version 5.0

  1. 1. June 23, 2016 Applications of 2D Surface Flow Modeling in the new HEC-RAS Version 5.0 ASFPM Annual National Conference, Grand Rapids, MI Concurrent Session G Derek Etkin, P.E.
  2. 2. Contents 1. Overview of HEC-RAS prior to 2D capabilities 2. Introduction to 2D Surface Flow Modeling in version 5.0 3. Applications of HEC-RAS 2D capability 4. Advantages and Opportunities 2
  3. 3. HEC-RAS Overview 3  Open channel flow freeware published by USACE  HEC-2 developed in 1966 (FORTRAN), HEC-RAS released in 1995  Generates flood profiles from 1D Open Channel Flow energy and continuity equations
  4. 4. HEC-RAS Overview  Cross sections developed from survey and LiDAR using HEC-GeoRAS, an extension in ArcMap 4 flowto
  5. 5. HEC-RAS Overview  Inundation mapping generated from profile interpolated between cross sections and intersected with terrain data 5 Source: FEMA (2013) Federal Guidelines for Inundation Mapping of Flood Risks Associated with Dam Incidents and Failures (FEMA P-946)
  6. 6. HEC-RAS Overview – Steady State  1-D Steady Flow – constant discharge 6 2 o f ( /A)Q h+ gA( - S + S )=0 x x α    Q=VA Momentum Continuity  Simulate single, peak discharge from hydrologic analysis
  7. 7. HEC-RAS Overview – Unsteady Flow  1-D Unsteady Flow – variable discharge and storage 7  Simulate routed hydrograph, storage between cross sections 2 o f ( /A)Q Q hgA( ) 0S St x x α         Q A+ =0 x t    Momentum Continuity
  8. 8. Representing with 2D Flow with 1D HEC-RAS 8  Split Flow
  9. 9. Representing with 2D Flow with 1D HEC-RAS 9  Offline Storage Areas
  10. 10. Introducing HEC-RAS version 5.0! 10
  11. 11. 2D Flow Areas in HEC-RAS 5.0 11  2D Flow Areas can be added to geometry file like Storage Areas  Digital Terrain Map now integrated into HEC-RAS input files  2D Flow Area properties imported from Digital Terrain Map
  12. 12. 2D Flow Areas in HEC-RAS 5.0 12
  13. 13. 2D Flow Area Calculations 13  Unstructured Mesh with Implicit Finite Volume solver  Hydraulic properties of computational cells (and faces) pre-processed from Digital Terrain Map  Diffusion Wave or Full Momentum 2D Equations Source: Brunner, G.W. (2014) Combined 1D and 2D Modeling with HEC-RAS Source: USACE (2016) HEC-RAS 2D Modeling User’s Manual (CPD-68A)
  14. 14. 2D Flow Area Calculations 14  Pre-processed stage-storage for each cell  Cells do not have a “flat bottom” or single depth. Cell Volume
  15. 15. 2D Flow Area Calculations 15  Pre-processed cross section for each cell face from Terrain Map  Conveyance between cells defined by rating curves Cell Face
  16. 16. 2D Flow Area Calculations 16  High resolution Digital Terrain Map  Lower resolution computational mesh
  17. 17. 2D Flow Area Linkages 17 2D Flow Areas can be linked to 1D Flow Reaches  1D Flow Reaches  Upstream  Downstream  Lateral Connections  Storage Areas or other 2D Flow Areas  External Boundary Condition  Normal Depth, Rating Curve, Stage or Flow time series
  18. 18. Post-Processing - Depth 18
  19. 19. Post-Processing - Depth 19
  20. 20. Post-Processing – Velocity 20
  21. 21. HEC-RAS 2D Riverine Applications 21 Useful for riverine flow outside of well-defined, single channels:  Inter-connected or braided channels  Dam breach flood waves with unpredictable paths
  22. 22. HEC-RAS 2D Example Application – Dam Breach 22
  23. 23. HEC-RAS 2D Example Application – Dam Breach 23
  24. 24. HEC-RAS 2D Applications – Dam Breach 24
  25. 25. HEC-RAS 2D Applications – Dam Breach 25
  26. 26. HEC-RAS 2D Technical Advantages 26  Implicit Finite Volume approach  Improved stability  Cells can start completely dry  More robust than finite element or finite difference  Allows for larger time steps than explicit methods  Unstructured Mesh Flexibility  Cells do not have flat bottom  Allows larger computational cells without loss of terrain details  Cells can be sized according to terrain features
  27. 27. HEC-RAS 2D Project Advantages 27  Public Domain  No license fees  Large community of practitioners  Widely accepted as HEC product  Pre- and Post-processing in MAPPER (and GeoRAS)  Can easily integrate 2D Flow Areas into existing HEC-RAS models  Update old 1D HEC-RAS models  No need to decide 1D or 2D when selecting modeling software  Can use for screening approach and where to focus detail
  28. 28. CHALLENGES  Mesh editing tools limited 28
  29. 29. CHALLENGES  Some limited capacity for modeling structures  Can represent weirs, levees, and culverts  Cannot use full 1D bridge modeling capabilities 29
  30. 30. CHALLENGES  Processing of map inundation, removing “islands” from high resolution grid; cleaning up “Leaking”  Can use hydraulic connectivity plots 30
  31. 31. CHALLENGES  Limited by quality of LiDAR/Raster…  Adding bathymetry to LiDAR for “pure” 2D Flow Area runs 31
  32. 32. Thank you. 32

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