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Watershed and Stream Network Delineation – Geomorphological Considerations

Watershed and Stream Network Delineation – Geomorphological Considerations. David G. Tarboton dtarb@cc.usu.edu. http://www.engineering.usu.edu/dtarb. Overview. Review of flow direction, accumulation and watershed delineation Topographic texture and drainage density

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Watershed and Stream Network Delineation – Geomorphological Considerations

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  1. Watershed and Stream Network Delineation – Geomorphological Considerations David G. Tarboton dtarb@cc.usu.edu http://www.engineering.usu.edu/dtarb

  2. Overview • Review of flow direction, accumulation and watershed delineation • Topographic texture and drainage density • Channel network geomorphology and Hortons Laws • Stream drop test to objectively oelect channel delineation threshold • Curvature and slope based methods to represent variable drainage density • The D approach • Specialized grid accumulation functions • TauDEM software

  3. 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.

  4. 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

  5. 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:

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

  7. 4 3 2 5 1 6 7 8 Eight Direction Pour Point Model D8 Band/GRASS/TARDEM Direction encoding

  8. Grid Network

  9. 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 TauDEM convention includes the area of the grid cell itself.

  10. 4 3 2 5 1 6 7 8 Direction encoding 1 2 3 1 1 7 6 5 2 1 7 6 5 3 6 7 7 Contributing area Programming the calculation of contributing area 2 2 3 6

  11. 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

  12. Watershed Draining to This Outlet

  13. 100 grid cell constant support area threshold stream delineation

  14. 200 grid cell constant support area based stream delineation

  15. AREA 2 3 AREA 1 12 How to decide on support area threshold ? Why is it important?

  16. 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.

  17. Delineation of Channel Networks and Subwatersheds 500 cell theshold 1000 cell theshold

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

  19. Logged Pacific Redwood Forest near Humboldt, California

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

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

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

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

  24. “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.

  25. 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

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

  27. Drainage Density Versus Contributing Area Threshold

  28. 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

  29. Bifurcation Ratio

  30. Area Ratio

  31. Length Ratio

  32. Slope Ratio

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

  34. Constant Stream Drops Law Broscoe, A. J., (1959), "Quantitative analysis of longitudinal stream profiles of small watersheds," Office of Naval Research, Project NR 389-042, Technical Report No. 18, Department of Geology, Columbia University, New York.

  35. Nodes Links Single Stream Note that a “Strahler stream” comprises a sequence of links (reaches or segments) of the same order Stream DropElevation difference between ends of stream

  36. Look for statistically significant break in constant stream drop property Break in slope versus contributing area relationship 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’.

  37. Statistical Analysis of Stream Drops

  38. T-Test for Difference in Mean Values 72 130 0 T-test checks whether difference in means is large (> 2) when compared to the spread of the data around the mean values

  39. Constant Support Area Threshold

  40. 200 grid cell constant support area based stream delineation

  41. 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

  42. Contributing area of upwards curved grid cells only

  43. Upward Curved Contributing Area Threshold

  44. Curvature based stream delineation

  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 Contributing Area

  46. Grid network pruned to order 4 stream delineation

  47. Slope area threshold (Montgomery and Dietrich, 1992).

  48. Addressing the limitations imposed by 8 grid directions

  49. ? Topographic Slope Topographic Definition Drop/Distance Limitation imposed by 8 grid directions. Flow Direction Field — if the elevation surface is differentiable (except perhaps for countable discontinuities) the horizontal component of the surface normal defines a flow direction field.

  50. The D Algorithm Tarboton, D. G., (1997), "A New Method for the Determination of Flow Directions and Contributing Areas in Grid Digital Elevation Models," Water Resources Research, 33(2): 309-319.) (http://www.engineering.usu.edu/cee/faculty/dtarb/dinf.pdf)

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