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

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

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

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

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

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

7. Terrain Analysis 71 56 44 5369 74 7872 69 47 68 58 55 21 31 67 58 4946 37 38 64 22 61 16 Digital elevation model (DEM) 2 2 2 2 2 2 4 4 4 4 11 24 8 128 124 1 4 1 Flow direction grid Flow accumulation grid 00 0 0 0 0 1 1 2 1 0 0 0 00 3 8 5 2 1 1 20 0 124 Stream Network Flow direction codes 1 2 4 8 16 32 64 128 Hydrologic functions

8. Terrain Analysis zDEM and digitized reach network

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

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

11. Terrain Analysis zFlow direction zWater flows to one of the eight neighbor cells, according to the direction of the steepest descent.

12. Terrain Analysis zFlow accumulation zMeasure of the drainage area in units of grid cells.

13. Stream-Watershed Delineation Stream Network Definition Watershed Delineation Watershed Outlet Definition Raster to Vector Conversion

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

15. Sub-Basins and Reach Network zReach network. zGrid 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 zReach segmentation. zReach 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. Watershed Outlet Definition Automatic Most downstream cells of the stream segments Interactive User-identified cells [outlets, reservoirs, control points, etc.] Watershed Outlets [Grid]

18. Sub-Basins and Reach Network zWatershed outlets. zThe 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 zModified reach segmentation. zThe user-defined outlets modify the reach segmentation by splitting the segments in which they are located.

20. Watershed Delineation Watershed Outlets

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

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

23. Merging Polygons and Watersheds Watershed Vectorization Stream Vectorization Merging Watersheds Dissolving Spurious Polygons

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

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

26. Merging Watersheds zAfter 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.