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Topographic Maps vs DEM

Topographic Maps vs DEM. Topographic Map 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. Outlet. Drainage direction.

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Topographic Maps vs DEM

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  1. Topographic Maps vs DEM

  2. Topographic Map1:24,000 Scalehttp://www.tnrcc.state.tx.us/gis/raster.html 20 ft contour 100 ft contour Stream Center Line

  3. Flow in Direction of Steepest Descent

  4. Watershed Delineation by Hand Digitizing Watershed divide Outlet Drainage direction

  5. 30 Meter MeshStandard for 1:24,000 Scale Maps

  6. 30 Meter DEM Cell Boundaries

  7. USGS 30 Meter DEM for This Area

  8. DEM Lattice Points

  9. DEM Cell Stores Elevation at Lattice Point

  10. DEM Elevations 720 720 Contours 740 720 700 680 740 720 700 680

  11. DEM Elevations Contours 700 680

  12. 67 56 49 46 50 53 44 37 38 48 58 55 22 31 24 61 47 21 16 19 53 34 12 11 12 Digital Elevation Model

  13. 67 56 49 46 50 53 44 37 38 48 58 55 22 31 24 61 47 21 16 19 53 34 12 11 12 Cell Definition 30 m cell 50 (cell value) cell

  14. Dealing with the Pits

  15. 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

  16. “Burning In” the Streams - Improve accuracy based on photograph  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 = +

  17. The Flow Direction Grid

  18. 32 64 128 16 1 8 4 2 Eight Direction Pour Point Model

  19. 67 56 49 53 44 37 58 55 22 Direction of Steepest Descent 1 1 67 56 49 53 44 37 58 55 22 Slope:

  20. 2 2 4 4 8 1 2 4 8 4 128 1 2 4 8 2 1 4 4 4 1 1 1 2 16 Flow Direction Grid

  21. 32 64 128 16 1 8 4 2 Flow Direction Grid- Red is NE

  22. Grid Network

  23. The Flow Accumulation Grid

  24. Flow Accumulation Grid 0 0 0 0 0 3 2 0 0 2 0 0 1 0 11 0 0 1 0 15 2 5 0 1 24 Count the # of contributing cells Grid Network

  25. Flow Accumulation Grid 0 0 0 0 0 0 3 2 2 0 0 1 0 0 11 0 0 0 1 15 1 0 2 5 24

  26. Defining the Stream Grid

  27. 0 0 0 0 0 0 3 2 2 0 0 1 0 0 11 0 0 0 1 15 1 0 2 5 24 Flow Accumulation > 5 Cell Threshold

  28. Stream Network for 5 cell Threshold Drainage Area 0 0 0 0 0 3 2 0 0 2 0 0 1 0 11 0 0 1 0 15 2 5 0 1 24

  29. Streams with 200 cell Threshold(>18 hectares or 13.5 acres drainage area)

  30. 1000 Cell Threshold Exceeded at Stream Junction 510 989 1504 (>1000)

  31. Defining Stream Segments

  32. 0 0 0 0 0 3 2 0 0 2 0 0 1 0 11 0 0 1 0 15 2 5 0 1 24 Stream Segments

  33. 1 1 2 1 2 3 5 3 3 5 4 4 4 4 4 6 6 6 Stream Segments in a Cell Network 5 5

  34. Creating Subwatersheds

  35. Watershed Outlet

  36. Watershed Draining to This Outlet

  37. Watershed andDrainage PathsDelineated from 30m DEM Automated method is more consistent than hand delineation

  38. Subwatersheds for Stream Segments Same Cell Value

  39. Vectorized Streams Linked Using Grid Code to Cell Equivalents Vector Streams Grid Streams

  40. Delineated Subwatersheds and Stream Networks

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