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Watershed and Stream Network Delineation

Watershed and Stream Network Delineation. Grid digital elevation models (DEM) Eight Direction Pour Point Model Contributing Area Pits and Pit Removal Channel Network Delineation Channel Network Geomorphology. Elevation Surface — the ground surface elevation at each point.

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Watershed and Stream Network Delineation

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  1. Watershed and Stream Network Delineation • Grid digital elevation models (DEM) • Eight Direction Pour Point Model • Contributing Area • Pits and Pit Removal • Channel Network Delineation • Channel Network Geomorphology

  2. Elevation Surface — the ground surface elevation at each point Digital Elevation Model — A digital representation of an elevation surface. Examples include a (square) digital elevation grid, triangular irregular network, set of digital line graph contours or random points.

  3. Digital Elevation Grid — a grid of cells (square or rectangular) in some coordinate system having land surface elevation as the value stored in each cell. Square Digital Elevation Grid — a common special case of the digital elevation grid

  4. DEM Data Sources • 30m DEMs from 1:24,000 scale maps • 3" (100m) DEMs from 1:250,000 scale maps • 15" DEM for the US resampled from 3” Dem • 30" DEM of the earth (GTOPO30)

  5. 30m DEMs • Best resolution standardized data source available for the US • Coverage of the country is incomplete • Data by 7.5’ map sheets in UTM projection • Link for US (USGS EROS Data Center) http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html

  6. 3” DEMs • Derived by US Defence Mapping Agency, available from USGS for the whole US • Data in geographic coordinates by 1;250,000 map sheet names (1ºx 1º) cells in (1ºx 2º) maps • Needs to be projected to planar coordinates • Link for US (USGS EROS Data Center) http://edcwww.cr.usgs.gov/doc/edchome/ndcdb/ndcdb.html

  7. Coverage of 30m and 3" DEMs 3" (100m) DEM 1º 30m DEM 7.5´ 7.5´ 1º

  8. Cell Size 30m 100m

  9. A Case Study of Hog Pen Creek Hog Pen Ck 4 km 4 km

  10. 20 ft contour 100 ft contour Stream Center Line Drainage direction Watershed Delineation by Hand Digitizing Watershed divide Outlet

  11. 30 Meter MeshStandard for 1:24,000 Scale Maps

  12. 720 720 Contours 740 720 700 680 740 720 700 680 DEM Elevations

  13. 67 56 49 52 48 37 58 55 22 Direction of Steepest Descent 30 30 67 56 49 52 48 37 58 55 22 Slope:

  14. 4 3 2 5 1 6 7 8 Eight Direction Pour Point Model D8

  15. Grid Network

  16. Contributing Area Grid 1 1 1 1 1 1 1 1 1 1 1 4 3 3 1 4 3 1 1 3 1 1 1 1 1 12 1 2 1 12 1 1 1 2 16 1 1 2 1 16 2 1 3 6 25 3 6 1 2 25

  17. 1 1 1 1 1 1 4 3 3 1 1 2 1 1 12 1 1 1 2 16 2 1 3 6 25 Contributing Area > 10 Cell Threshold

  18. Watershed Draining to This Outlet

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

  20. 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

  21. AREA 2 3 AREA 1 12 How to decide on support area threshold ?

  22. Streams from 1:250,000 blue lines

  23. 100 grid cell constant support area threshold stream delineation

  24. 200 grid cell constant support area based stream delineation

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

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

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

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

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

  30. Contrasting Interpretations “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.) “any definition of a finite channel network is arbitrary, and entirely scale dependent.” (Band, 1993, in “Channel Network Hydrology”, edited by Beven and Kirkby, p15.)

  31. Suggestion: One contributing area threshold does not fit all watersheds. Lets look at some geomorphology. • Drainage Density • Horton’s Laws • Stream Drops • Slope-Area properties • Hack’s Law

  32. 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

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

  34. Drainage Density Versus Contributing Area Threshold

  35. 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

  36. Bifurcation Ratio

  37. Length Ratio

  38. Area Ratio

  39. Slope Ratio

  40. Constant Stream Drops

  41. Slope-Area scaling Data from Reynolds Creek 30 m DEM, 50 grid cell threshold, points, individual links, big dots, bins of size 100

  42. Hack’s Law

  43. Break in slope versus contributing area scaling Break in Constant stream drop property Physical basis in the form instability theory of Smith and Bretherton (1972), see Tarboton et al. 1992 Suggestion: Map channel networks from the DEM at the finest resolution consistent with observed channel network geomorphology ‘laws’.

  44. Constant Support Area Threshold

  45. Channel network delineation, other options 4 3 2 1 1 1 1 1 1 1 1 1 1 5 6 7 1 1 1 4 2 3 2 2 3 1 1 Grid Order 8 1 1 1 2 1 1 1 1 3 12 1 1 1 1 1 1 2 1 16 3 1 2 1 1 2 3 6 2 25 3 Accumulation Area

  46. Grid network pruned to order 4 stream delineation

  47. Curvature based stream delineation

  48. Local Curvature Computation(Peuker and Douglas, 1975, Comput. Graphics Image Proc. 4:375) 43 48 48 51 51 56 41 47 47 54 54 58

  49. Contributing area of upwards curved grid cells only

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