1. Processing Elevation Data

2. Limitations of DEMs for hydro work Dates Static, does not evolve Matching to linear line work due to scale Processing errors Interpretation errors Lack of ground truth Artificial versus real peaks and sinks

3. Getting line work

10. Creating the stream for our watershed

11. 24k streams for the major basin extent

13. Clipped streams to watershed bnd

14. Braid in stream network

15. Aerial photo investigating braid

16. Sinks Depressions in the DEM where water gets trapped A sink prohibits calculating future flow direction grid values. A sink occurs when all neighboring cells are higher than the processing cell. Sometimes they are natural features!

19. Filled DEM

20. Flow direction Created from an elevation surface Direction values are assigned Flow direction grids are used in many hydro GIS functions Flow direction map 3264128 1 24 8 16

21. Flow direction Created from an elevation surface Direction values are assigned Flow direction grids are used in the other flow functions Flow direction map 3264128 1 24 8 16

24. Flow accumulation The accumulated flow is based upon the number of cells flowing into each cell in the output grid. The current processing cell is not considered in this accumulation. Output cells with a high flow accumulation are areas of concentrated flow and may be used to identify stream channels. Output cells with a flow accumulation of zero are local topographic highs and may be used to identify ridges

27. Summary of spatial tools available within ArcGIS Elevation grid Flow direction Fill sinks Allows for additional landscape based analysis Flow accumulation Any sinks? Yes No Watersheds Stream delineations Riparian areas Stream order

28. Calculate drainage area Flow accumulation grid = tells us the number of cells of a certain area that flow to a point

29. Calculate drainage area So, if there are 280,721 cells that flow to that location… and each cell is 10m by 10m in size (100m 2 ) Then The total drainage area is (280,721) * (100) = 28,072,100 m 2 Or 28,072,100 m 2 * 0.00024718 = 6,938 acres Conversion of m 2 to acre

30. Vector versus raster streams

32. Other issues

33. Creating a raster stream grid

34. Result of streamgrid

35. Thin command to thin the raster

36. Results of thin

37. Changing all nonstream values to ND

38. Result

39. Raising the elevation by 100m

40. Finding the focal min values of dem for raster streams

41. Con’t

42. Result of elevation values to streams

43. Finds the nodata values

44. Result

45. Actual burn

46. Result

48. Summary Used 24K lines from NHD for reference Clipped streams to watershed boundary fill, flow direction, flow accumulation Drainage area calculation Raster streams, thinned Raised off stream elevation values Assigned true elevations to stream cells Combined the two for a hydrological “corrected” elevation surface

49. Questions / Comments?