STREAM RESTORATION AWRA Summer Specialty Conference, GIS and Water Resources IX

Transcription

1 STREAM RESTORATION 2016 AWRA Summer Specialty Conference, GIS and Water Resources IX Innovative Use of 2D Hydraulic Modeling in Stream Restoration Design Presented by: Li Gao, PE and Robert Scrafford, PE

2 PRESENTATION OVERVIEW Introduction 1-D vs. 2-D comparison Model set up Tour through example results from HEC-RAS 5.0 Creating robust stream designs

3 INTRODUCTION MODELED STREAM 2.84 square mile drainage area 5,151 feet long 45% impervious (includes Redskin Stadium parking lots) Urbanized channel

4 EXISTING CONDITIONS Knickpoints at culvert outfalls Bank erosion Degraded ecosystem Exposed utility lines

5 HYDRAULIC PARAMETERS FOR STREAM RESTORATION Velocity Field Bed Shear Stress Bank Shear Stress Stream Power for Sediment Transport 100-year Water Surface

6 1-D VS. 2-D COMPARISON 2-D 1-D Rich and Precise Topography No Cross Section and Ineffective Area Set Up Contraction, Expansion and Bend Loss Depth Average Two Dimensional Velocity and Water Surface Discontinuous Geometry Ineffective Area Cross Section Set Up Contraction and Expansion Bend Loss Average Velocity and Water surface

7 HEC-RAS 2D MODEL SET UP Model geometry domain file generated from the survey data Create a land use map to define the roughness of geometry domain Define boundary conditions Mesh generation with break line set up at critical locations Computation interval selection Initial condition set up Run HEC-RAS 2D model Generate output data

8 GEOMETRY DEVELOPMENT Survey File (CAD) Raster File (ARCGIS) Terrain File (ARCGIS)

9 REACH DOMAIN ENTIRE STUDY DOMAIN EXISTING CONDITION PROPOSED CONDITION

10 LAND USE MAP

11 BOUNDARY CONDITIONS Downstream Normal Depth Upstream Inflows 2500 Upstream Boundary Hydrograph 2000 Discharge(cfs) :00 2:24 4:48 7:12 9:36 12:00 14:24 16:48 19:12 Time (hr) Upper Reach Tributary One Tributary Two Tributary Three Tributary Four

12 DOMAIN CONDITIONS CELL (MESH) SIZE 3 X 3 MAIN CHANNEL AREA 10 X10 FLOODPLAIN AREA AND STUDY REACH AREA TIME INTERVAL 1 SECOND INITIAL CONDITION DRY LAND

13 FLOODPLAIN LIMITS

14 WATER DEPTH FOR 100-YEAR STORM

15 VELOCITY FIELD VELOCITTY (FPS) WATER DEPTH CONTOUR CULVERT OUTFALL RIVER BEND RIFFLE AND POOL SEQUENCE

16 SHEAR STRESS SHEAR STRESS (PSF) WATER DEPTH CONTOUR CULVERT OUTFALL RIVER BEND RIFFLE AND POOL SEQUENCE

17 STREAM POWER STREAM POWER (LB.FT.S) STREAM POWER (LB.FT.S) EXISTING PROPOSED

18 MESH SETUP FOR OPTIMAL ANALYSIS No survey topo here Flat area; larger mesh Bed and banks- 3 x 3 Floodplain- 10 x 10

19 BULLETPROOF DESIGN- SHEAR STRESS Shear stress for treatments, bed, banks Compare to acceptable thresholds Try to match bed shear to incipient motion threshold 2.5 psf banks 3.0 psf bed Permissible Shear

20 BULLETPROOF DESIGN- VELOCITY Bed: 10 fps Banks: 6 fps Permissible Velocity

21 ANALYZE STREAM STRUCTURES- SHEAR STRESS Put the structure in the terrain Analyze the shear Compare to permissible levels for rock size Pools: gravel Steps: Imbricated stone Structure extents Pool Step Pool Make sure rock extends

22 Pools: 1-inch gravel ANALYZE STREAM STRUCTURES- VELOCITY Step: Imbricated over 24-inches Step Pool Pool

23 LATE STAGES OF FLOOD- VELOCITY WATER DEPTH (FT) FLOW DEPTH AT FLOOD PEAK PERIOD FLOW DEPTH AT FLOOD RECESSION PERIOD

24 LATE STAGES OF FLOOD- SHEAR STRESS SHEAR STRESS (FPS) SHEAR STRESS AT FLOOD PEAK PERIOD SHEAR STRESS AT FLOOD RECESSION PERIOD

25 FLOODPLAIN MODELING- VELOCITY Analysis of 100-year flood; 5 fps exiting BMP Berms to prevent concentration or stone to protect Stormwater BMP

26 USACE PERMITTING STATUS Before After USACE still requesting 1-D model Need to standardize submission It s a matter of time before it is accepted

27 SUMMARY HEC-RAS 5.0 is here! Superior to 1-D modeling Powerful tool to evaluate hydraulic parameters Stream power shows trends of sediment transport RAS Mapper an effective tool to view and analyze 2-D results Use to develop robust stream design

28 QUESTIONS?