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Floodplain Mapping using HEC-RAS and ArcView GIS

Floodplain Mapping using HEC-RAS and ArcView GIS. http://www.ce.utexas.edu/stu/tateec. Eric Tate Francisco Olivera David Maidment. Outline. Motivation and Objectives HEC-RAS Hydraulic Model Stream Cross-Section Mapping GIS Data Models 3-D Terrain Modeling Floodplain Mapping.

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Floodplain Mapping using HEC-RAS and ArcView GIS

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  1. Floodplain Mapping using HEC-RAS and ArcView GIS http://www.ce.utexas.edu/stu/tateec Eric Tate Francisco Olivera David Maidment

  2. Outline • Motivation and Objectives • HEC-RAS Hydraulic Model • Stream Cross-Section Mapping • GIS Data Models • 3-D Terrain Modeling • Floodplain Mapping

  3. Map-Based Hydrology and Hydraulics ArcView Input Data DEM ArcView Flood plain maps CRWR-PrePro HEC-RAS Water surface profiles HEC-HMS Flood discharge

  4. Motivation: Why map floodplains in GIS? • Computer automation results in time and resource savings versus manual floodplain plotting • Flood insurance rate determination • Economic impact analysis and flood early warning systems • Design of drainage control structures, including storm drains, culverts, and bridges

  5. Objectives • Develop procedure to process computed water surface profiles generated from HEC-RAS hydraulic modeling anddraw floodplain maps in ArcView GIS • Synthesize a TIN terrain model from HEC-RAS cross-sectional data and a digital elevation model (DEM)

  6. Outline • Motivation • HEC-RAS Hydraulic Model • Stream Cross-Section Mapping • GIS Data Models • 3-D Terrain Modeling • Floodplain Mapping

  7. HEC-RAS: Background • Hydraulic model of the U.S. Army Corps of Engineers • Input = cross-section geometry and flow rates • Output = flood water elevations Cross-Section Schematic

  8. HEC-RAS: Cross-Section Representation • Points describe channel and floodway geometry • Bank station locations • Water surface elevations and floodplain boundaries

  9. HEC-RAS: Output Graphical Text File

  10. HEC-RAS: Data Translation • Data translation from HEC-RAS output text file to dbase table • Table data includes the river station IDs, various cross-section coordinates, reach lengths, & computed flood elevations

  11. Outline • Motivation • HEC-RAS Hydraulic Model • Stream Cross-Section Mapping • GIS Data Models • 3-D Terrain Modeling • Floodplain Mapping

  12. Stream Centerline Mapping • Digital orthophotograph and road coverage used as a base map • User defines stream centerline • Definition points identify key stream cross-sections

  13. Cross-Section Mapping One to one relationship established between table records and definition points

  14. Cross-Section Mapping • Assume straight line cross-sections • Proportional aliasing for cross-section location • User input for cross-section orientation

  15. Outline • Motivation • HEC-RAS Hydraulic Model • Stream Cross-Section Mapping • GIS Data Models • 3-D Terrain Modeling • Floodplain Mapping

  16. GIS Data Models: Vector Points, lines, and polygons Typically used for linear feature representation

  17. GIS Data Models: Raster Digital Elevation Model (DEM) Square grid cells Typically used for steady-state spatial modeling and two-dimensional surface representation

  18. GIS Data Models: TIN Triangular Irregular Network (TIN) Mesh of equilateral triangles Used for three-dimensional surface representation and drainage analysis.

  19. Outline • Motivation • HEC-RAS Hydraulic Model • Stream Cross-Section Mapping • GIS Data Models • 3-D Terrain Modeling • Floodplain Mapping

  20. 3D Terrain Modeling: Procedure Outside Channel: Raster Inside Channel: Vector Result: TIN

  21. 3D Terrain Modeling: Procedure DEM raster to vector conversion Form polygon bounding the cross-sections Delete any DEM points falling within the bounding polygon

  22. 3D Terrain Modeling Problem: elevation differences at the end of the cross-section

  23. 3D Terrain Modeling Re-sample cross sections to eliminate elevation differences

  24. 3D Terrain Modeling Build TIN model from re-sampled cross-sections and DEM

  25. Outline • Motivation • HEC-RAS Hydraulic Model • Stream Cross-Section Mapping • GIS Data Models • 3-D Terrain Modeling • Floodplain Mapping

  26. Floodplain Mapping: 3D View

  27. Floodplain Mapping: Ultimate Goal

  28. Floodplain Mapping: Plan View

  29. HEC-RAS: Output Graphical Text File

  30. Floodplain Mapping: Plan View • Raster floodplain shows both extent and depth of flooding • Digital orthophotograph base map allows easy comparison of floodplain location with specific areas of interest (e.g., infrastructure, buildings)

  31. Real-time flood mapping Nexrad radar rainfall input Real time Precomputed flood map library Offline Flood hydrology analysis system

  32. Questions?Comments? Also thanks to Seann Reed and Brian Adams

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