1. Topographic Maps vs DEM

2. Topographic Map 1:24,000 Scale http://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 Drainage direction Outlet

5. 30 Meter Mesh Standard 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 Contours 720 700 680 740 680700720740 720

11. DEM Elevations Contours 700 680

12. 6756494650 121112 5344373848 5855223124 6147211619 3453 Digital Elevation Model

13. 6756494650 121112 5344373848 5855223124 6147211619 3453 50 30 m cell cell (cell value) Cell Definition

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

17. + =  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

18. The Flow Direction Grid

19. 32 16 8 64 4 128 1 2 Eight Direction Pour Point Model

20. 675649 534437 585522 1 675649 534437 585522 1 Slope: Direction of Steepest Descent

21. 22448 1216 12484 1281248 21444 11 Flow Direction Grid

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

23. Grid Network

24. The Flow Accumulation Grid

25. 00000 0 0 0 0 0 0 0 0 032 2 11 1 1 15 25 24 1 Flow Accumulation Grid Grid Network Count the # of contributing cells

26. 00 0 00 0 0 0 0 0 0 0 0 0 322 11 1 1 1 2 15 245 Flow Accumulation Grid

27. Defining the Stream Grid

28. 00 0 00 0 0 0 0 0 0 0 0 0 322 11 1 1 1 2 15 245 Flow Accumulation > 5 Cell Threshold

29. Stream Network for 5 cell Threshold Drainage Area 00000 0 0 0 0 0 0 0 0 032 2 11 1 1 15 25 24 1

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

31. 989510 1504 (>1000) 1000 Cell Threshold Exceeded at Stream Junction

32. Defining Stream Segments

33. 00000 0 0 0 0 0 0 0 0 032 2 11 1 1 15 25 24 1 Stream Segments

34. 5 5 1 1 1 3 2 2 3 3 4 4 4 4 4 5 5 6 6 6 Stream Segments in a Cell Network

35. Creating Subwatersheds

36. Watershed Outlet

37. Watershed Draining to This Outlet

38. Watershed and Drainage Paths Delineated from 30m DEM Automated method is more consistent than hand delineation

39. Same Cell Value Subwatersheds for Stream Segments

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

41. Delineated Subwatersheds and Stream Networks