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Stream and WatershedDelineation from DEM’s
David Maidment, Ph.D. and Francisco Olivera, Ph.D.Center for Research in Water Resources
University of Texas at Austin
Texas Department of Transportation (TxDOT)Water Resources Modeling Using GIS2000 - Austin, Texas
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Overview
Study area in West Austin with a USGS 30-meter DEM from a 1:24,000 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, 1:24,000 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
Drainage directionOutlet
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200-Meter Mesh
1km
1km
Universal Transverse Mercator (UTM) Coordinates
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100-Meter Mesh
100m
100m
1km
1km
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30-Meter Mesh
Standard for 1:24,000 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
700
680
740
680700720740
720 720
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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 1:24,000 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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67 56 49 46 50
12 11 12
53 44 37 38 48
58 55 22 31 24
61 47 21 16 19
3453
Digital Elevation Model
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67 56 49 46 50
12 11 12
53 44 37 38 48
58 55 22 31 24
61 47 21 16 19
3453
50
cell size
cell
(cell value)
Cell Definition
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32
16
8
64
4
128
1
2
Eight-Direction Pour-Point Model
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67 56 49
53 44 37
58 55 22
1
67 56 49
53 44 37
58 55 22
1
26.162
4467
14
1
5367
Slope:
Direction of Steepest Descent
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2 2 4 4 8
1 2 16
1 2 4 8 4
128 1 2 4 8
2 1 4 4 4
11
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
32
16
8
64
4
128
1
2
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0 0 000
0
0
0
0
0
0
0
0
032 2
111
115
2 524 1
0 0 00 0
0
0
0
0
0
0
0
0
0
3 2 2
11 1
1
12
15
245
Flow Accumulation Grid
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Overview
Study area in West Austin with a USGS 30-meter DEM from a 1:24,000 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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0 0 00 0
0
0
0
0
0
0
0
0
0
3 2 2
11 1
1
12
15
245
Flow Accumulation Threshold
Flow Accumulation > 5 cells
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Stream Network
0 0 000
0
0
0
0
0
0
0
0
032
2
111
115
2 5
241
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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+ =
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
Burning-in the 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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Overview
Study area in West Austin with a USGS 30-meter DEM from a 1:24,000 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 Draining to an Outlet
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DEM-Based Delineation
Found error hand delineation!!!
Watershed and flow paths
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0 0 000
0
0
0
0
0
0
0
0
03 2 2
111
115
2 5
241
Stream Segments (Links)
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55
11
3
22
334 4 4
4 45
5
666
Stream Segments Grid
3
6
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9895101504 (>1000)
Threshold at Stream Junction
1000 cell threshold exceeded at stream junction.
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Same Cell Value
Sub-Watersheds
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Stream Vectorization
VectorStreams
GridStreams
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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 1:24,000 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 DEM’s from 1:24,000 scale maps
3" (100-m) DEM’s from 1:250,000 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 DEM’s
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/glisbin/guide.pl/glis/hyper/guide/usgs_dem
Link for Texas:ftp://www.tnris.state.tx.us/tnris/demA.html
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3” DEM’s
Derived by US Defence Mapping Agency, available from USGS for the whole US.
Data in geographic coordinates by 1:250,000 map sheet names (1°x 1°) cells in (1°x 2°) maps
Needs to be projected to planar coordinates
Link:http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html
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7.5´
7.5´
1º
1º
3" (100m) DEM
30m DEM
Coverage of 30-m and 3" DEM’s
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Cell Size30m 100m
30-m and 3" DEM’s
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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/gtopo30.html
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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.
DEM’s 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