Topographic Maps vs DEM
description
Transcript of Topographic Maps vs DEM
![Page 1: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/1.jpg)
Topographic Maps vs DEM
![Page 2: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/2.jpg)
Topographic Map1:24,000 Scale
http://www.tnrcc.state.tx.us/gis/raster.html
20 ft contour
100 ft contour
Stream Center Line
![Page 3: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/3.jpg)
Flow in Direction of Steepest Descent
![Page 4: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/4.jpg)
Watershed Delineation by Hand Digitizing
Watershed divide
Drainage direction Outlet
![Page 5: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/5.jpg)
30 Meter MeshStandard for 1:24,000 Scale Maps
![Page 6: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/6.jpg)
30 Meter DEM Cell Boundaries
![Page 7: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/7.jpg)
USGS 30 Meter DEM for This Area
![Page 8: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/8.jpg)
DEM Lattice Points
![Page 9: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/9.jpg)
DEM Cell Stores Elevation at Lattice Point
![Page 10: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/10.jpg)
DEM ElevationsContours
720
700
680
740
680700720740
720 720
![Page 11: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/11.jpg)
DEM Elevations Contours
700
680
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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
![Page 13: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/13.jpg)
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
30 m cell
cell
(cell value)
Cell Definition
![Page 14: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/14.jpg)
Dealing with the Pits
![Page 15: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/15.jpg)
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
![Page 16: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/16.jpg)
![Page 17: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/17.jpg)
+ =
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 - Improve accuracy based on photograph
![Page 18: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/18.jpg)
The Flow Direction Grid
![Page 19: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/19.jpg)
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
26.1624467
=−
141
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
![Page 22: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/22.jpg)
Flow Direction Grid- Red is NE
32
16
8
64
4
128
1
2
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Grid Network
![Page 24: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/24.jpg)
The Flow Accumulation Grid
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0 0 000
0
0
0
0
0
0
0
0
03 2 2
11 1
1 152 5
24 1
Flow Accumulation Grid
Grid Network Count the # of contributing cells
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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 Grid
![Page 27: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/27.jpg)
Defining the Stream Grid
![Page 28: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/28.jpg)
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
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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
![Page 30: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/30.jpg)
Streams with 200 cell Threshold(>18 hectares or 13.5 acres drainage area)
![Page 31: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/31.jpg)
9895101504 (>1000)
1000 Cell Threshold Exceeded at Stream Junction
![Page 32: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/32.jpg)
Defining Stream Segments
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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
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55
11
1
3
22
334 4 4
4 45
5
666
Stream Segments in a Cell Network
![Page 35: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/35.jpg)
Creating Subwatersheds
![Page 36: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/36.jpg)
Watershed Outlet
![Page 37: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/37.jpg)
Watershed Draining to This Outlet
![Page 38: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/38.jpg)
Watershed and Drainage Paths Delineated from 30m DEM
Automated method is more consistent than hand delineation
![Page 39: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/39.jpg)
Same Cell Value
Subwatersheds for Stream Segments
![Page 40: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/40.jpg)
Vectorized Streams Linked Using Grid Code to Cell Equivalents
VectorStreams
GridStreams
![Page 41: Topographic Maps vs DEM](https://reader036.fdocuments.net/reader036/viewer/2022081604/5681683d550346895dde0aee/html5/thumbnails/41.jpg)
Delineated Subwatersheds and Stream Networks