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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

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

what is crwr prepro
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)

what is hec hms
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.
what is hec hms4
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.

stream watershed delineation
Stream-Watershed Delineation

Terrain Analysis

Stream-Watershed Delineation

terrain analysis
Terrain Analysis

Burn-In Streams

[Grid]

DEM[Grid]

Fill Sinks

[Grid]

DigitizedStream Network[Line Coverage]

Flow Direction

[Grid]

Flow Accumulation

[Grid]

terrain analysis7

2

4

2

4

2

2

2

2

4

4

1

1

8

2

4

128

1

2

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128

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64

128

1

128

4

128

1

1

16

Flow direction grid

4

2

8

Flow direction codes

Terrain Analysis

58

78

72

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Hydrologic functions

56

49

46

69

53

44

37

38

58

64

55

22

31

68

61

21

47

16

Digital elevation model (DEM)

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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

terrain analysis8
Terrain Analysis
  • DEM and digitized reach network
terrain analysis9

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38

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60

34

40

50

60

58

31

30

53

58

31

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53

50

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22

Digitized creek

DEM creek

145

138

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38

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144

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22

150

145

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22

Raised DEM

Burned-in DEM

Digitized creek

Terrain Analysis

Burning-in streams

terrain analysis10
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.
terrain analysis11
Terrain Analysis
  • Flow direction
  • Water flows to one of the eight neighbor cells, according to the direction of the steepest descent.
terrain analysis12
Terrain Analysis
  • Flow accumulation
  • Measure of the drainage area in units of grid cells.
stream watershed delineation13
Stream-Watershed Delineation

Stream NetworkDefinition

Watershed OutletDefinition

Raster to VectorConversion

Watershed Delineation

stream network definition

AutomaticCells draining more area than a user-defined threshold value.

InteractiveCells located downstream of user-identified cells.

Stream Network[Grid]

Stream Network Definition
sub basins and reach network
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.
sub basins and reach network16
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.
watershed outlet definition

AutomaticMost downstream cells of the stream segments

InteractiveUser-identified cells[outlets, reservoirs, control points, etc.]

Watershed Outlets[Grid]

Watershed Outlet Definition
sub basins and reach network18
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.
sub basins and reach network19
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.
watershed delineation
Watershed Delineation

Watershed Outlets

Watershed Delineation

sub basins and reach network21
Sub-Basins and Reach Network
  • Sub-basin delineation.
  • The drainage area of each sub-basin outlet is delineated.
vectorization
Vectorization
  • Streams and watersheds are converted from raster to vector format.
merging polygons and watersheds
Merging Polygons and Watersheds

WatershedVectorization

StreamVectorization

Dissolving SpuriousPolygons

MergingWatersheds

merging spurious polygons
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.
merging watersheds
Merging Watersheds
  • Adjacent watershed polygons can be merged into a single polygon, if they share the outlet or one flows into the other.
merging watersheds26
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.