DEM’s, Watershed and Stream Network Delineation DEM Data Sources Study Area in West Austin with a...
65
DEM’s, Watershed and Stream Network Delineation • DEM Data Sources • Study Area in West Austin with a USGS 30m DEM from a 1:24,000 scale map • Eight direction pour point model (flow direction and flow accumulation grids) • Stream network definition • Watershed delineation
-
Upload
jesse-norris -
Category
Documents
-
view
219 -
download
0
Transcript of DEM’s, Watershed and Stream Network Delineation DEM Data Sources Study Area in West Austin with a...
DEM’s, Watershed and Stream Network Delineation
• DEM Data Sources • Study Area in West Austin with a USGS
30m 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
• Shuttle Radar Topography Mission (SRTM)
• 30m DEMs from 1:24,000 scale map
• 1” National Elevation Dataset
• 3" (100m) DEMs from 1:250,000 scale maps
• 30" DEM of the earth (GTOPO30)
http://srtm.usgs.gov/srtmimagegallery/index.html
Santa Barbara, California
http://srtm.usgs.gov/srtmimagegallery/index.html
San Andreas Fault, California
http://srtm.usgs.gov/srtmimagegallery/index.html
Salt Lake City, Utah
http://srtm.usgs.gov/srtmimagegallery/index.html
Mt Kilimanjaro, Tanzania
Shuttle Radar Topography Mission (SRTM)
• 1 arc-second elevation data for the United States, 3 arc-second data for the globe
• Produced by radar measurements from a Shuttle mission, Feb 11-22, 2000
• http://srtm.usgs.gov/data/obtainingdata.html
Interferometry used by SRTMIn interferometry, two images are taken from different vantage points of the same area. The slight difference in the two images allows scientists to determine the height of the surface.
SRTM Coverage 56°S to 60°N
30m 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/glisbin/guide.pl/glis/hyper/guide/usgs_dem
• Link for Texas http://www.tnris.state.tx.us/DigitalData/DEMs/dems.htm
National Elevation Dataset
• Seamless 1” DEM for the US in 1° x 1° blocks
• Compiled by synthesizing the 30m DEM’s from 1:24,000 scale maps
• Link to website http://edcnts12.cr.usgs.gov/ned/
Seamless Data Distribution
http://edcnts14.cr.usgs.gov/Website/store/viewer.htm
http://seamless.usgs.gov/
7.5´
7.5´
1º
1º
1” and 3” DEMs
30m DEM
Coverage of 30m, 1” and 3" DEMs
3” DEMs
• Derived by US Defence Mapping Agency, available from USGS for the whole US
• Data in geographic coordinates by 1;250,000 map sheet names (1ºx 1º) cells in (1ºx 2º) maps
• Needs to be projected to planar coordinates• Link http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html
Cell Size30m 100m
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
• Data must be projected before use• Link http://edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo30.html
GTOPO30
Source: http://edcwww.cr.usgs.gov/landdaac/gtopo30/gtopo30.html
Drainage in North America
Source: http://edcwww.cr.usgs.gov/landdaac/gtopo30/hydro/namerica.html
Drainage Basins of North America
Source: http://edcwww.cr.usgs.gov/landdaac/gtopo30/hydro/na_basins.html
DEM’s, Watershed and Stream Network Delineation
• DEM Data Sources • Study Area in West Austin with a USGS
30m DEM from a 1:24,000 scale map• Eight direction pour point model (flow
direction and flow accumulation grids)• Stream network definition• Watershed delineation
Study Region in West Austin
Hog Pen Ck
4 km
4 km
Topographic MapAustin West, 1:24,000 Scale
http://www.tnrcc.state.tx.us/gis/raster.html
20 ft contour
100 ft contour
Stream Center Line
Flow in Direction of Steepest Descent
Watershed Delineation by Hand Digitizing
Watershed divide
Drainage direction Outlet
200 Meter Mesh (Universal Transverse Mercator Coordinates)
1km
1km
100 Meter Mesh (UTM Coordinates)
100m
100m
1km
1km
30 Meter MeshStandard for 1:24,000 Scale Maps
Austin West 30 Meter DEMElevations in meters
ftp://ftp.tnris.state.tx.us/tnris/demA.html
USGS 30 Meter DEM for This Area
30 Meter DEM Cell Boundaries
DEM Lattice Points
DEM Cell Stores Elevation at Lattice Point
DEM Elevations
Contours
720
700
680
740
680700720740
720 720
DEM Elevations Contours
700
680
DEM’s, Watershed and Stream Network Delineation
• DEM Data Sources • Study Area in West Austin with a USGS
30m DEM from a 1:24,000 scale map• Eight direction pour point model (flow
direction and flow accumulation grids)• Stream network definition• Watershed delineation
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
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
32
16
8
64
4
128
1
2
Eight Direction Pour Point Model
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
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
Austin West 30 Meter DEMElevations in meters
ftp://ftp.tnris.state.tx.us/tnris/demA.html
Flow Direction Grid
32
16
8
64
4
128
1
2
Grid Network
DEM’s, Watershed and Stream Network Delineation
• DEM Data Sources • Study Area in West Austin with a USGS
30m DEM from a 1:24,000 scale map• Eight direction pour point model (flow
direction and flow accumulation grids)• Stream network definition• Watershed delineation
0 0 000
0
0
0
0
0
0
0
0
03 2 2
11 1
1 152 5
24 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
Link to Grid calculator
0 0 00 0
0
0
0
0
0
0
0
0
0
3 2 2
11 1
1
12
15
245
Flow Accumulation > 5 Cell Threshold
Stream Network for 5 cell Threshold Drainage Area
0 0 000
0
0
0
0
0
0
0
0
03 2 2
111
115
2 5
241
Streams with 200 cell Threshold(>18 hectares or 13.5 acres drainage area)
+ =
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 Produces "burned in" DEM streams = mapped streams
“Burning In” the Streams
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
DEM’s, Watershed and Stream Network Delineation
• DEM Data Sources • Study Area in West Austin with a USGS
30m DEM from a 1:24,000 scale map• Eight direction pour point model (flow
direction and flow accumulation grids)• Stream network definition• Watershed delineation
Watershed Outlet
Watershed Draining to This Outlet
Watershed and Drainage Paths Delineated from 30m DEM
Automated method is more consistent than hand delineation
0 0 000
0
0
0
0
0
0
0
0
03 2 2
111
115
2 5
241
Stream Segments
55
11
1
3
22
334 4 4
4 45
5
666
Stream Segments in a Cell Network
9895101504 (>1000)
1000 Cell Threshold Exceeded at Stream Junction
Same Cell Value
Subwatersheds for Stream Segments
Vectorized Streams Linked Using Grid Code to Cell Equivalents
VectorStreams
GridStreams
Delineated Subwatersheds and Stream Networks
Summary Concepts
• 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
Summary Concepts (2)
• DEM cell elevation is at the cell center
• eight direction pour point model leads to flow direction and flow accumulation grids
• stream network is defined as cells whose flow accumulation exceeds a threshold
• watershed outlet is the cell with highest flow accumulation
Summary Concepts (3)
• Streams can be divided into links and subwatersheds defined for them
• Resulting grids can be vectorized
• Standardized DEM data sources: 30m, 1” 3”, 30”
• Coverage from local scale to the whole earth
