Texas Department of Transportation Tx DOT Water Resources

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

What is CRWR-Pre. Pro? Digital Spatial Data z CRWR-Pre. Pro is an Arc. View pre-processor of digital spatial data for the HEC’s Hydrologic Modeling System (HMS) CRWR-Pre. Pro Data for HEC-HMS Input Components (Not all HMS options are included yet)

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

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

Stream-Watershed Delineation Terrain Analysis Stream-Watershed Delineation

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

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

Terrain Analysis z DEM and digitized reach network

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

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

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

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

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

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]

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

Sub-Basins and Reach Network z Reach segmentation. z 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.

Watershed Outlet Definition Automatic Most downstream cells of the stream segments Interactive User-identified cells [outlets, reservoirs, control points, etc. ] Watershed Outlets [Grid]

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

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

Watershed Delineation Watershed Outlets Watershed Delineation

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

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

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

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

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

Merging Watersheds z After merging subbasin polygons, the attribute tables are modified so that the watershed code (Wsh. Code) of the reaches and the area of the new sub-basin are updated.