Stream and Watershed Delineation from DEM

1
Stream and WatershedDelineation from DEMs
Texas Department of Transportation (TxDOT) Water
Resources Modeling Using GIS 2000 - Austin, Texas

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

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Overview

• Study area in West Austin with a USGS 30-meter
  DEM from a 124,000 scale map
• Eight direction pour point model (flow direction
  and flow accumulation grids)
• Stream network definition
• Watershed delineation
• DEM data sources

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Study Region in West Austin
Hog Pen Creek
4 km
4 km
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Topographic Map
20 ft contour
100 ft contour
Stream Center Line
Austin West, 124,000 Scale http//www.tnrcc.state
.tx.us/gis/raster.html
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Direction of Steepest Descent
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Watershed Delineation by Hand
Watershed divide
Outlet
Drainage direction
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200-Meter Mesh
1km
1km
Universal Transverse Mercator (UTM) Coordinates
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100-Meter Mesh
1km
100m
1km
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30-Meter Mesh
Standard for 124,000 Scale Maps
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Austin West 30-Meter DEM
Elevations in meters. ftp//ftp.tnris.state.tx.us/
tnris/demA.html
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USGS 30-Meter DEM
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30 Meter DEM Cell Boundaries
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DEM Lattice Points
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DEM Lattice Points
DEM Cells Store Elevation at Lattice Point
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DEM Elevations
720
720
740
720
700
680
720
680
700
740
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DEM Elevations
700
680
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Overview

• Study area in West Austin with a USGS 30-meter
  DEM from a 124,000 scale map
• Eight direction pour point model (flow direction
  and flow accumulation grids)
• Stream network definition
• Watershed delineation
• DEM data sources

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Digital Elevation Model
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Cell Definition
cell size
50
(cell value)
cell
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Eight-Direction Pour-Point Model
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Direction of Steepest Descent
1
1
67
56
49
53
44
37
58
55
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Slope
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Flow Direction Grid
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Austin West 30-Meter DEM
Elevations in meters. ftp//ftp.tnris.state.tx.us/
tnris/demA.html
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Flow Direction Grid
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Grid Network
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Flow Accumulation Grid
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Overview

• Study area in West Austin with a USGS 30-meter
  DEM from a 124,000 scale map
• Eight direction pour point model (flow direction
  and flow accumulation grids)
• Stream network definition
• Watershed delineation
• DEM data sources

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Flow Accumulation Threshold
Flow Accumulation gt 5 cells
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Stream Network
Stream network for a 5-cell threshold drainage
area.
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Stream Network
Stream network for a 13.5-acres threshold
drainage area (200 cells).
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Burning-in the Streams
? Take a mapped stream network and a DEM ? Make a
grid of the streams ? Raise the off-stream DEM
cells by an arbitrary elevation increment ?
Burned-in DEM streams Mapped streams


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Filling in the Pits

• DEM creation results in artificial pits in the
  landscape
• A pit is a set of one or more cells which has no
  downstream cells around it
• Unless these pits are filled they become sinks
  and isolate portions of the watershed
• Pit filling is first thing done with a DEM

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(No Transcript)
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Overview

• Study area in West Austin with a USGS 30-meter
  DEM from a 124,000 scale map
• Eight direction pour point model (flow direction
  and flow accumulation grids)
• Stream network definition
• Watershed delineation
• DEM data sources

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Watershed Outlet
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Watershed Draining to an Outlet
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DEM-Based Delineation
Found error hand delineation!!!
Watershed and flow paths
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Stream Segments (Links)
0
0
0
0
0
0
3
2
0
2
0
0
1
0
11
0
0
1
0
15
2
5
0
1
24
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Stream Segments Grid
5
3
5
6
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Threshold at Stream Junction
989
510
1504 (gt1000)
1000 cell threshold exceeded at stream junction.
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Sub-Watersheds
Same Cell Value
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Stream Vectorization
Grid Streams
Vector Streams
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Stream and Sub-Watersheds
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Overview

• Study area in West Austin with a USGS 30-meter
  DEM from a 124,000 scale map
• Eight direction pour point model (flow direction
  and flow accumulation grids)
• Stream network definition
• Watershed delineation
• DEM data sources

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DEM Data Sources

• 30-m DEMs from 124,000 scale maps
• 3" (100-m) DEMs from 1250,000 scale maps
• 15" (500-m) DEM for the US resampled from 3 DEM
• 30" (1-Km) DEM of the earth (GTOPO30)

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30-m DEMs

• Best resolution standardized data source
  available for the US
• Coverage of the country is incomplete
• Data by 7.5 map sheets in UTM projection
• Link for US http//edcwww.cr.usgs.gov/Webglis/gli
  sbin/guide.pl/glis/hyper/guide/usgs_dem
• Link for Texas
• ftp//www.tnris.state.tx.us/tnris/demA.html

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3 DEMs

• Derived by US Defence Mapping Agency, available
  from USGS for the whole US.
• Data in geographic coordinates by 1250,000 map
  sheet names (1x 1) cells in (1x 2) maps
• Needs to be projected to planar coordinates
• Link
• http//edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb
  .html

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Coverage of 30-m and 3" DEMs
3" (100m) DEM
30m DEM
1º
7.5
7.5
1º
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30-m and 3" DEMs
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15" DEM

• Derived by USGS from 3" DEMs by resampling each
  fifth point
• Best resolution for seamless coverage of the US
  in a single grid
• Projected cell size is 500m
• Link
• http//nsdi.usgs.gov/nsdi/wais/water/gcip.HTML

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30" DEM GTOPO30

• Produced by USGS from 3" grids and Digital Chart
  of the World topography
• Coverage complete for the earth
• Projected cell size is 1km approximately
• Data must be projected before use
• Link
• http//edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo3
  0.html

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30" DEM GTOPO30
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Drainage in North America
Source http//edcwww.cr.usgs.gov/landdaac/gtopo30
/hydro/namerica.html
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Summary Concepts (1)

• Topographic maps are the traditional way of
  representing land surface terrain and streams.
• Watersheds can be hand-delineated from these
  maps.
• DEMs of equivalent accuracy are now available
  for most map series in the US.
• DEM cell elevation is at the cell center.
• Eight direction pour point model leads to flow
  direction and flow accumulation grids.

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Summary Concepts (2)

• Stream network is defined as cells whose flow
  accumulation exceeds a threshold.
• Streams can be divided into links and
  sub-watersheds defined for them.
• Watershed outlet is the cell with highest flow
  accumulation.
• Resulting grids can be vectorized.
• Standardized DEM data sources 30m, 3, 15, 30,
  which cover from local scale to the whole earth