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CRWR-PrePro Stream and Watershed Delineation

Texas Department of Transportation (TxDOT) Water Resources Modeling Using GIS 2000 - Austin, Texas. CRWR-PrePro Stream and Watershed Delineation. Francisco Olivera, Ph.D. Center for Research in Water Resources University of Texas at Austin. What is CRWR-PrePro?.

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CRWR-PrePro Stream and Watershed Delineation

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  1. Texas Department of Transportation (TxDOT) Water Resources Modeling Using GIS 2000 - Austin, Texas CRWR-PreProStream and Watershed Delineation Francisco Olivera, Ph.D. Center for Research in Water Resources University of Texas at Austin

  2. What is CRWR-PrePro? • CRWR-PrePro is an ArcView pre-processor of digital spatial data for the HEC’s Hydrologic Modeling System (HMS) Digital Spatial Data CRWR-PrePro Data for HEC-HMS Input Components (Not all HMS options are included yet)

  3. What is HEC-HMS? • HEC-HMS “is a new generation software for precipitation-runoff simulation that supersedes the HEC-1 Flood Hydrograph Package.” (HEC-HMS User’s Manual) • HEC-HMS is a Windows version of HEC-1.

  4. What is HEC-HMS? Control Definition of the analysis time window. BasinDefinition of the hydrologic elements. HEC-HMS Simulation Hydrographs Precipitation Definition of rainfall data in time and space.

  5. Stream-Watershed Delineation Terrain Analysis Stream-Watershed Delineation

  6. Terrain Analysis Burn-In Streams [Grid] DEM[Grid] Fill Sinks [Grid] DigitizedStream Network[Line Coverage] Flow Direction [Grid] Flow Accumulation [Grid]

  7. 2 4 2 4 2 2 2 2 4 4 1 1 8 2 4 128 1 2 4 128 32 64 128 1 128 4 128 1 1 16 Flow direction grid 4 2 8 Flow direction codes Terrain Analysis 58 78 72 71 69 74 67 Hydrologic functions 56 49 46 69 53 44 37 38 58 64 55 22 31 68 61 21 47 16 Digital elevation model (DEM) 0 0 0 0 0 0 1 2 1 1 8 0 3 2 5 0 1 20 1 0 0 0 0 1 24 Flow accumulation grid Stream Network

  8. Terrain Analysis • DEM and digitized reach network

  9. 45 38 44 45 45 38 44 45 40 34 50 60 34 40 50 60 58 31 30 53 58 31 30 53 50 45 32 22 50 45 32 22 Digitized creek DEM creek 145 138 144 145 38 145 38 144 145 140 134 150 160 34 140 34 150 160 158 131 130 153 30 158 131 30 153 150 145 132 122 22 150 145 132 22 Raised DEM Burned-in DEM Digitized creek Terrain Analysis Burning-in streams

  10. Terrain Analysis • Burned-in DEM • Elevation is increased by a fixed value in all cells, except for those that coincide with the digitized reach network.

  11. Terrain Analysis • Flow direction • Water flows to one of the eight neighbor cells, according to the direction of the steepest descent.

  12. Terrain Analysis • Flow accumulation • Measure of the drainage area in units of grid cells.

  13. Stream-Watershed Delineation Stream NetworkDefinition Watershed OutletDefinition Raster to VectorConversion Watershed Delineation

  14. AutomaticCells draining more area than a user-defined threshold value. InteractiveCells located downstream of user-identified cells. Stream Network[Grid] Stream Network Definition

  15. Sub-Basins and Reach Network • Reach network. • Grid cells draining more than a user-defined threshold value (blue streams), or located downstream of user-defined cells (red streams) are part of the reach network.

  16. Sub-Basins and Reach Network • Reach segmentation. • Reach segments (links) are the sections of a reach channel connecting two successive junctions, a junction and an outlet, or a headwater and a junction.

  17. AutomaticMost downstream cells of the stream segments InteractiveUser-identified cells[outlets, reservoirs, control points, etc.] Watershed Outlets[Grid] Watershed Outlet Definition

  18. Sub-Basins and Reach Network • Watershed outlets. • The most downstream cells of the reach segments (brown cells), and user-defined cells (red dots) are potential sub-basin outlets.

  19. Sub-Basins and Reach Network • Modified reach segmentation. • The user-defined outlets modify the reach segmentation by splitting the segments in which they are located.

  20. Watershed Delineation Watershed Outlets Watershed Delineation

  21. Sub-Basins and Reach Network • Sub-basin delineation. • The drainage area of each sub-basin outlet is delineated.

  22. Vectorization • Streams and watersheds are converted from raster to vector format.

  23. Merging Polygons and Watersheds WatershedVectorization StreamVectorization Dissolving SpuriousPolygons MergingWatersheds

  24. Merging Spurious Polygons • Cells connected to the main watershed polygon through a corner are defined as a separate polygon (spurious polygon). • These polygons are dissolved into the main polygon.

  25. Merging Watersheds • Adjacent watershed polygons can be merged into a single polygon, if they share the outlet or one flows into the other.

  26. Merging Watersheds • After merging sub-basin polygons, the attribute tables are modified so that the watershed code (WshCode) of the reaches and the area of the new sub-basin are updated.

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