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Watershed and Stream Network Delineation Geomorphological Considerations David G. Tarboton dtarb@cc.usu.edu http://www.engineering.usu.edu/dtarb Slide 2 Overview n Review of flow direction, accumulation and watershed delineation n Topographic texture and drainage density n Channel network geomorphology and Hortons Laws n Stream drop test to objectively oelect channel delineation threshold n Curvature and slope based methods to represent variable drainage density n The D approach n Specialized grid accumulation functions n TauDEM software Slide 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. Slide 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 Slide 5 675649 524837 585522 30 675649 524837 585522 30 Slope: Direction of Steepest Descent Slide 6 32 16 8 64 4 128 1 2 Eight Direction Pour Point Model ESRI Direction encoding Slide 7 4 5 6 3 7 2 1 8 Eight Direction Pour Point Model D8 Band/GRASS/TARDEM Direction encoding Slide 8 Grid Network Slide 9 11111 1 1 1 1 1 1 1 1 143 3 12 2 2 16 36 25 2 11 1 11 1 1 1 1 1 1 1 1 1 433 12 1 2 2 3 16 256 Contributing Area Grid TauDEM convention includes the area of the grid cell itself. Slide 10 Programming the calculation of contributing area 5 1 8 7 6 3 2 4 5 6 5 6 7 7 6 7 7 Direction encoding 2 2 6 3 1 1 1 2 3 1 2 3 Contributing area Slide 11 11 1 11 1 1 1 1 1 1 1 1 1 433 12 2 2 2 3 16 256 Contributing Area > 10 Cell Threshold Slide 12 Watershed Draining to This Outlet Slide 13 100 grid cell constant support area threshold stream delineation Slide 14 200 grid cell constant support area based stream delineation Slide 15 How to decide on support area threshold ? AREA 1 AREA 2 3 12 Why is it important? Slide 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. Slide 17 Delineation of Channel Networks and Subwatersheds 500 cell theshold 1000 cell theshold Slide 18 Examples of differently textured topography Badlands in Death Valley. from Easterbrook, 1993, p 140. Coos Bay, Oregon Coast Range. from W. E. Dietrich Slide 19 Logged Pacific Redwood Forest near Humboldt, California Slide 20 Canyon Creek, Trinity Alps, Northern California. Photo D K Hagans Slide 21 Gently Sloping Convex Landscape From W. E. Dietrich Slide 22 Mancos Shale badlands, Utah. From Howard, 1994. Slide 23 Topographic Texture and Drainage Density Same scale, 20 m contour interval Sunland, CA Driftwood, PA Slide 24 Lets look at some geomorphology. Drainage Density Hortons Laws Slope Area scaling Stream Drops 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.) Suggestion: One contributing area threshold does not fit all watersheds. Slide 25 Drainage Density D d = L/A Hillslope length 1/2D d L B B Hillslope length = B A = 2B L D d = L/A = 1/2B B= 1/2D d Slide 26 Drainage Density for Different Support Area Thresholds EPA Reach Files100 grid cell threshold1000 grid cell threshold Slide 27 Drainage Density Versus Contributing Area Threshold Slide 28 Hortons Laws: Strahler system for stream ordering 1 1 1 1 1 1 1 1 1 1 1 1 1 1 2 2 2 2 3 Slide 29 Bifurcation Ratio Slide 30 Area Ratio Slide 31 Length Ratio Slide 32 Slope Ratio Slide 33 Slope-Area scaling Data from Reynolds Creek 30 m DEM, 50 grid cell threshold, points, individual links, big dots, bins of size 100 Slide 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. Slide 35 Stream Drop Elevation difference between ends of stream Note that a Strahler stream comprises a sequence of links (reaches or segments) of the same order Nodes Links Single Stream Slide 36 Suggestion: Map channel networks from the DEM at the finest resolution consistent with observed channel network geomorphology laws. 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 Slide 37 Statistical Analysis of Stream Drops Slide 38 T-Test for Difference in Mean Values 72130 0 T-test checks whether difference in means is large (> 2) when compared to the spread of the data around the mean values Slide 39 Constant Support Area Threshold Slide 40 200 grid cell constant support area based stream delineation Slide 41 Local Curvature Computation (Peuker and Douglas, 1975, Comput. Graphics Image Proc. 4:375) 43 41 48 47 48 4754 51 54 5156 58 Slide 42 Contributing area of upwards curved grid cells only Slide 43 Upward Curved Contributing Area Threshold Slide 44 Curvature based stream delineation Slide 45 Channel network delineation, other options 4 5 6 3 7 2 1 8 11 1 11 1 1 1 1 1 1 1 1 1 433 12 2 2 2 3 16 256 Contributing Area 11 1 11 1 1 1 1 1 1 1 1 1 222 3 1 1 1 2 3 32 Grid Order Slide 46 Grid network pruned to order 4 stream delineation Slide 47 Slope area threshold (Montgomery and Dietrich, 1992). Slide 48 Addressing the limitations imposed by 8 grid directions Slide 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. Slide 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) Slide 51 Specific catchment area a is the upslope area per unit contour length [m 2 /m m] Upslope contributing area a Stream line Contour line Slide 52 Contributing Area using D8 Contributing Area using D Slide 53 Useful for example to track where sediment or contaminant moves Slide 54 Useful for example to track where a contaminant may come from Slide 55 Useful for a tracking contaminant or compound subject to decay or attenuation Slide 56 Transport limited accumulation Useful for modeling erosion and sediment delivery, the spatial dependence of sediment delivery ratio and contaminant that adheres to sediment Slide 57 Reverse Accumulation Useful for destabilization sensitivity in landslide hazard assessment with Bob Pack Slide 58 TauDEM Software Functionality n Pit removal (standard flooding approach) n Flow directions and slope u D8 (standard) u D (Tarboton, 1997, WRR 33(2):309) u Flat routing (Garbrecht and Martz, 1997, JOH 193:204) n Drainage area (D8 and D ) n Network and watershed delineation u Support area threshold/channel maintenance coefficient (Standard) u Combined area-slope threshold (Montgomery and Dietrich, 1992, Science, 255:826) u Local curvature based (using Peuker and Douglas, 1975, Comput. Graphics Image Proc. 4:375) n Threshold/drainage density selection by stream drop analysis (Tarboton et al., 1991, Hyd. Proc. 5(1):81) n Wetness index and distance to streams n Specialized grid analysis functions (Upslope influence, Downslope dependence, Decaying accumulation, Concentration limited accumulation, Downslope accumulation, Transport limited accumulation) Slide 59 TauDEM in ArcGIS ESRI binary grid ASCII text grid ESRI gridio API (Spatial analyst) USU TMDLtoolkit modules (grid, shape, image, dbf, map, mapwin) TauDEM C++ library Fortran (legacy) components Standalone command line applications C++ COM DLL interface Visual Basic GUI application Visual Basic ESRI ArcGIS 8.1 Toolbar Vector shape files Data formats Available from http://www.engineering.usu.edu/dtarb/ Binary direct access grid Slide 60 Demonstration