CRWRPrePro Stream and Watershed Delineation

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CRWR-PreProStream and Watershed Delineation
Texas Department of Transportation (TxDOT) Water
Resources Modeling Using GIS 2000 - Austin, Texas

• Francisco Olivera, Ph.D.
• Center for Research in Water Resources
• University of Texas at Austin

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What is CRWR-PrePro?
Digital Spatial Data

• CRWR-PrePro is an ArcView pre-processor of
  digital spatial data for the HECs Hydrologic
  Modeling System (HMS)

CRWR-PrePro
Data for HEC-HMS Input Components (Not all HMS
options are included yet)
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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
  Users Manual)
• HEC-HMS is a Windows version of HEC-1.

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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.
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Stream-Watershed Delineation
Terrain Analysis
Stream-Watershed Delineation
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Terrain Analysis
Burn-In Streams Grid
DEMGrid
Fill Sinks Grid
DigitizedStream NetworkLine Coverage
Flow Direction Grid
Flow Accumulation Grid
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Terrain Analysis
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Hydrologic functions
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53
69
37
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58
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31
64
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47
21
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Digital elevation model (DEM)
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0
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1
1
2
1
0
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8
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5
0
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1
20
0
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1
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Flow accumulation grid
Stream Network
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Terrain Analysis

• DEM and digitized reach network

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Terrain Analysis
Burning-in streams

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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.

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Terrain Analysis

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

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Terrain Analysis

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

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Stream-Watershed Delineation
Stream NetworkDefinition
Watershed OutletDefinition
Raster to VectorConversion
Watershed Delineation
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Stream Network Definition
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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.

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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.

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Watershed Outlet Definition
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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.

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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.

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Watershed Delineation
Watershed Outlets
Watershed Delineation
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Sub-Basins and Reach Network

• Sub-basin delineation.
• The drainage area of each sub-basin outlet is
  delineated.

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Vectorization

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

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Merging Polygons and Watersheds
WatershedVectorization
StreamVectorization
Dissolving SpuriousPolygons
MergingWatersheds
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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.

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Merging Watersheds

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

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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.