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Digital Elevation Model Based Watershed and Stream Network Delineation

Digital Elevation Model Based Watershed and Stream Network Delineation. Conceptual Basis Eight direction pour point model (D8) Flow accumulation Pit removal and DEM reconditioning Stream network delineation Catchment and watershed delineation Topographic texture and drainage density

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Digital Elevation Model Based Watershed and Stream Network Delineation

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  1. Digital Elevation Model Based Watershed and Stream Network Delineation • Conceptual Basis • Eight direction pour point model (D8) • Flow accumulation • Pit removal and DEM reconditioning • Stream network delineation • Catchment and watershed delineation • Topographic texture and drainage density • Channel network geomorphology and Horton’s Laws • Stream drop test to objectively select channel delineation threshold • Generalized methods for stream network delineation (Curvature, Slope-area, Grid order)

  2. Duality between Terrain and Drainage Network • Flowing water erodes landscape and carries away sediment sculpting the topography • Topography defines drainage direction on the landscape and resultant runoff and streamflow accumulation processes

  3. Study Area in West Austin with a USGS 30m DEM from a 1:24,000 scale map Watershed Delineation by Hand Digitizing Watershed divide Drainage direction Outlet ArcHydro Page 57

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

  5. 80 80 74 74 63 63 69 69 67 67 56 56 60 60 52 52 48 48 Hydrologic Slope - Direction of Steepest Descent 30 30 Slope: ArcHydro Page 70

  6. 32 64 128 16 1 8 4 2 Eight Direction Pour Point Model ESRI Direction encoding ArcHydro Page 69

  7. 2 2 4 4 8 1 2 4 8 4 32 64 128 128 1 2 4 8 16 1 2 1 4 4 4 8 4 2 1 1 1 2 16 Flow Direction Grid ArcHydro Page 71

  8. 32 64 128 16 1 8 4 2 Flow Direction Grid

  9. Grid Network ArcHydro Page 71

  10. Flow Accumulation Grid. Area draining in to a grid cell 0 0 0 0 0 0 0 0 0 0 0 3 2 2 0 3 2 0 0 2 0 1 0 0 11 0 0 1 0 11 0 0 0 1 15 0 0 1 0 15 1 0 2 5 24 2 5 0 1 24 Link to Grid calculator ArcHydro Page 72

  11. 1 1 1 1 1 4 3 1 1 3 1 1 1 1 1 1 4 3 3 1 1 1 2 1 12 1 2 1 1 12 1 1 2 1 16 1 1 1 2 16 3 6 1 2 2 1 3 6 25 25 Contributing Area Grid TauDEM convention. The area draining each grid cell including the grid cell itself.

  12. 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

  13. 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

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

  15. Watershed Draining to Outlet

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

  17. The Pit Removal Problem • 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 removed they become sinks and isolate portions of the watershed • Pit removal is first thing done with a DEM

  18. Pit Filling Increase elevation to the pour point elevation until the pit drains to a neighbor

  19. Carving Lower elevation of neighbor along a predefined drainage path until the pit drains to the outlet point

  20. Filling Minimizing Alterations Carving

  21. “Burning In” the Streams  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 = +

  22. AGREE Elevation Grid Modification Methodology

  23. 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

  24. 1 1 2 1 2 3 5 3 3 5 4 4 4 4 4 6 6 6 Stream Links in a Cell Network 5 5 ArcHydro Page 74

  25. Stream links grid for the San Marcos subbasin 201 172 202 203 206 204 Each link has a unique identifying number 209 ArcHydro Page 74

  26. Vectorized Streams Linked Using Grid Code to Cell Equivalents Vector Streams Grid Streams ArcHydro Page 75

  27. DrainageLines are drawn through the centers of cells on the stream links. DrainagePoints are located at the centers of the outlet cells of the catchments ArcHydro Page 75

  28. Catchments for Stream Links Same Cell Value

  29. Catchment GridID DEM GridCode 4 3 5 Vector Polygons Raster Zones Raster Zones and Vector Polygons One to one connection

  30. Catchments • For every stream segment, there is a corresponding catchment • Catchments are a tessellation of the landscape through a set of physical rules

  31. Catchments, DrainageLines and DrainagePoints of the San Marcos basin ArcHydro Page 75

  32. Adjoint catchment: the remaining upstream area draining to a catchment outlet. ArcHydro Page 77

  33. Catchment, Watershed, Subwatershed. Subwatersheds Catchments Watershed Watershed outlet points may lie within the interior of a catchment, e.g. at a USGS stream-gaging site. ArcHydro Page 76

  34. Summary of Key Processing Steps • [DEM Reconditioning] • Pit Removal (Fill Sinks) • Flow Direction • Flow Accumulation • Stream Definition • Stream Segmentation • Catchment Grid Delineation • Raster to Vector Conversion (Catchment Polygon, Drainage Line, Catchment Outlet Points)

  35. Delineation of Channel Networks and Catchments 500 cell theshold 1000 cell theshold

  36. AREA 2 3 AREA 1 12 How to decide on stream delineation threshold ? Why is it important?

  37. Hydrologic processes are different on hillslopes and in channels. It is important to recognize this and account for this in models. Drainage area can be concentrated or dispersed (specific catchment area) representing concentrated or dispersed flow.

  38. Examples of differently textured topography Badlands in Death Valley.from Easterbrook, 1993, p 140. Coos Bay, Oregon Coast Range. from W. E. Dietrich

  39. Logged Pacific Redwood Forest near Humboldt, California

  40. Canyon Creek, Trinity Alps, Northern California. Photo D K Hagans

  41. Gently Sloping Convex Landscape From W. E. Dietrich

  42. Mancos Shale badlands, Utah. From Howard, 1994.

  43. Same scale, 20 m contour interval Driftwood, PA Sunland, CA Topographic Texture and Drainage Density

  44. “landscape dissection into distinct valleys is limited by a threshold of channelization that sets a finite scale to the landscape.” (Montgomery and Dietrich, 1992, Science, vol. 255 p. 826.) Lets look at some geomorphology. • Drainage Density • Horton’s Laws • Slope – Area scaling • Stream Drops Suggestion:One contributing area threshold does not fit all watersheds.

  45. Drainage Density • Dd = L/A • Hillslope length  1/2Dd B B Hillslope length = B A = 2B L Dd = L/A = 1/2B  B= 1/2Dd L

  46. Drainage Density for Different Support Area Thresholds EPA Reach Files 100 grid cell threshold 1000 grid cell threshold

  47. Drainage Density Versus Contributing Area Threshold

  48. Hortons Laws: Strahler system for stream ordering 1 3 1 2 1 2 1 1 1 1 1 2 2 1 1 1 1 1 1

  49. Bifurcation Ratio

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