David G. Tarboton
July 18, 2001
Utah State University
8200 Old Main Hill
Logan, UT 84322-8200
TauDEM is a still somewhat experimental effort to develop a graphical user interface version of my programs that have been available in command line version for several years. This program is Copyright (C) 2001 David Tarboton, Utah State University. This program is distributed for free in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
Download taudem.exe. The installation package and software was built for Windows 98.
Click on commands and buttons below to go to the help for them.
The tools in the button bar are used to navigate within the project, and to execute functions.
These buttons start a new TauDEM project, open an exsiting project from a *.tdp file or save the current project in a *.tdp file.
Zoom to full extents
This button scales the map window to the extents of the current project.
This tool allows the user to view a smaller region of the map in greater depth. Click in the map window on the region of study. When the zoom in feature is selected, a left mouse click will zoom in, and a right mouse click will zoom out. To zoom to a specific area, left click and drag the mouse to enclose the area. The view will then zoom to those extents.
When selected, this tool will show more of the map in less detail. A left click will zoom out; a right click will reverse the process.
Zoom to previous extents
This will get back the last position of the map on the map window. It can be used along with Zoom-in and Zoom-out to get the desired view of the map. When the user zooms in/out mistakenly, he can use this tool to get back at his previous view.
This tool moves the portion of the map on display in the map window. Click on a region of the map and drag the mouse; dragging to the left will display the map to the right, and vice versa.
This tool is used to select grid cells or graphical objects. At present this is used for the selection of outlet points.
This button allows users to add a new layer in the project. At present bitmap images and shape files are the only data formats supported. Data layers added should have consistent geographic projections.
Remove Selected Layer
This tool will remove the selected layer from the project. Layers may be selected by clicking in the layer list window.
Clear all layers
To remove all the layers from the map window.
Layer Order arrows
These arrows control the order in which layers are displayed. Layers at the top in the legend are displayed on top of lower layers.
If drop analysis is checked, then the threshold is searched between the lowest and highest values given, using the number of steps given on a log scale. For the science behind the drop analysis see Tarboton et al. (1991, 1992), Tarboton and Ames (2001). The smallest threshold in the set searched with absolute value of the t statistic less than 2 is selected. This is done automatically during the River Network Raster (Upstream of Outlets) step. The threshold selected is saved in the threshold variable so may be inspected afterwards by viewing the options window.
The "Drop Analysis" command displays a table showing the information
used in the drop analysis, as follows
The columns are:
Threshold: The threshold used in the network delineation algorithm.
Dd: The drainage density (inverse length units - typically m) of the resulting network.
n1: Number of first order streams (Strahler ordering) in network with specified threshold.
nh: Number of higher order streams (Sequential segments of the same order are counted as one Strahler stream) in network with specified threshold.
md1: Mean drop (elevation difference between start and end) of first order streams.
mdh: Mean drop of higher order streams.
sd1: Standard deviation of first order stream drops.
sdh: Standard deviation of higher order stream drops.
t: Students t statistic for the difference between the first order and higher order mean stream drops.
The procedure suggested in Tarboton et al. (1991, 1992) and Tarboton and Ames (2001) is to select the smallest threshold for which the absolute value of the t statistic is less than 2. This selects the highest resolution network consistent with the "constant drop law". In the display above the threshold of 50 would be selected. It is worthwhile to view the drop analysis because the threshold steps are sometimes quite coarse, so the user may want to use the Specify Method Options command to change the number of intervals and lowest and highest values used in the search. Also it can occur that a large threshold is "correct" but a small threshold results in second or higher order streams also extending into the region that should not be streams. If these dominate the sample the following sequence of t statistics might result:
<2, <2, <2, >2, >2, <2, <2, ...
The automatic procedure in these cases would pick the lowest threshold, but it is probably better (and this is admittedly subjective, unfortunately) to pick the 6th threshold. In making this judgement I feel that it is best to consider many things, like sample sizes (is the t statistic robust), the visual impression in comparison to contour crenulations, and the drainage density that would result from a Slope versus Area plot as discussed in Tarboton et al., (1991, 1992). The automated procedure is therefore not foolproof and some degree of judgement and subjectivity is required.
The variables under 'Parameter' and 'Initial Conditions' can be assigned a fixed value or be set to be read from a look-up table associated with a variable classification grid by selecting the radio buttons. If the option of look-up table is chosen the user has to load the appropriate grid-table pair. Also, the user has to assign each variable the corresponding grid-table pair and the field in the table, from which the value has to be read. Combo boxes under 'Value from the look up table' help in making the selections. The lookup table should be a comma delimited text file with one header row and first column giving the key to associate parameters in the table with classification values in the corresponding grid. Following is an example of a lookup table:
Soil_type_number,f (m^-1),k(m/h),dth1,dth2,soil name,depth(metres)Parameter values in each model element are computed by averaging over all the grid cells for that model element based on table lookups above. In case the grid associate with a lookup table has no data at a location within a model element the fixed parameter value is used at that location. Therefore the fixed value parameters serve as defaults, even when table lookup is being used.
The checkboxes on the right (under calibration) control whether resulting model element parameters can be calibrated by multiplying by a factor to retain the spatial patterns provided through the GIS information in the classification grid.
Rain Coordinate file and Flow Coordinate file are the files required by the module to generate the output files, that are Model Specification file and Basin Parameter file. Rain Coordinate file is a shape file (extension '.shp') that contains the raingage point locations. The flow coordinate file has not been implemented yet.
Topmodel uses a histogram discretization of the topographic wetness index (ln(a/S) from the wetness index function above). The parameters in the right pane control the bin size associated with this histogram. Topmodel also uses a histogram discretization of overland flow distances to channels (computed with the distance to stream function above). The parameters in the right pane control the bin size associated with this histogram.
The kinematic wave flow routing part of TOPNET needs channel widths. These are estimated based on geomorphology using the drainage area and the hydraulic geometry function with parameters in the right pane.
Topmodel estimates the rainfall input to each model element using weights based upon delauney triangles. The delayney triangle check box controls the output of a grid depicting these triangles so that they may be displayed.
Pits in digital elevation data are defined as grid elements or sets of grid elements surrounded by higher terrain that, in terms of the DEM, do not drain. These are rare in natural topography and generally assumed to be artifacts arising due to the discrete nature and data errors in the preparation of the DEM. They are eliminated here using a 'flooding' approach. This raises the elevation of each pit grid cell within the DEM to the elevation of the lowest pour point on the perimeter of the pit . Slopes and Flow Directions
Working with grid DEMs slope may be computed as the difference in elevation between two adjacent cells divided by the distance between them. In dealing with flow this is usually done in a forward downwards direction. The slope associated with a cell is the slope from the cell to a downslope neighbor. This makes sense because it is where water will go. Radiation computations sometimes use slope based upon central finite difference methods. The earliest and simplest method for specifying flow directions is to assign flow from each grid cell to one of its eight neighbors, either adjacent or diagonally, in the direction with steepest downward slope. This method, designated D8 (8 flow directions), was introduced by O'Callaghan and Mark (1984) and has been widely used. The D8 approach has disadvantages arising from the discretization of flow into only one of eight possible directions, separated by 45odeg; . These have motivated the development of other methods comprising multiple flow direction methods , random direction methods and grid flow tube methods . Tarboton (1997) discusses the relative merits of these.
In the D¥ method, the flow direction angle measured counter clockwise from east is represented as a continuous quantity between 0 and 2p. This angle is determined as the direction of the steepest downward slope on the eight triangular facets formed in a 3 x 3 grid cell window centered on the grid cell of interest as illustrated in figure 1. A block-centered representation is used with each elevation value taken to represent the elevation of the center of the corresponding grid cell. Eight planar triangular facets are formed between each grid cell and its eight neighbors. Each of these has a downslope vector which when drawn outwards from the center may be at an angle that lies within or outside the 45o (p/4 radian) angle range of the facet at the center point. If the slope vector angle is within the facet angle, it represents the steepest flow direction on that facet. If the slope vector angle is outside a facet, the steepest flow direction associated with that facet is taken along the steepest edge. The slope and flow direction associated with the grid cell is taken as the magnitude and direction of the steepest downslope vector from all eight facets. This is implemented using equations given in Tarboton (1997).
Figure 1. Flow direction defined as steepest downward slope on planar triangular facets on a block centered grid.
In the case where no slope vectors are positive (downslope), the flow direction is set using the method of Garbrecht and Martz (1997) for the determination of flow across flat areas. This makes flat areas drain away from high ground and towards low ground. The D¥ method is preferred for the computation of flow directions on hillslopes where D8 grid bias is significant in the calculation of specific catchment area. D8 is still used for the definition of channel networks because we can not (have not yet learned to) work with channel networks that bifurcate in a downwards direction.
The contributing area programs check for edge contamination . This is defined as the possibility that a contributing area value may be underestimated due to grid cells outside of the domain not being counted. This occurs when drainage is inwards from the boundaries or areas with no data values for elevation. The algorithm recognizes this and reports no data for the contributing area. It is common to see streaks of no data values extending inwards from boundaries along flow paths that enter the domain at a boundary. This is the desired effect and indicates that contributing area for these grid cells is unknown due to it being dependent on terrain outside of the domain of data available. The edge contamination checking may be overridden with an option in the River Network and Watersheds/Method Options form in cases where you know this is not an issue or want to ignore these problems, if for example the DEM has been clipped along a watershed outline.
ncols 480 nrows 450 xllcorner 378923 yllcorner 4072345 cellsize 30 nodata_value -32768 43 3 45 7 3 56 2 5 23 65 34 6 32 etc 35 45 65 34 2 6 78 4 38 44 89 3 2 7 etc etcThe first row of data is at the top of the data set, moving from left to right. Cell values should be delimited by spaces. No carriage returns are necessary at the end of each row in the data set. The number of columns in the header is used to determine when a new row begins. The number of cell values must be equal to the number of rows times the number of columns.
Grid naming convention.
The following default naming convention is suggested and used by the
software. Any file names may be used with interactive input, but
I suggest sticking to this convention to avoid confusion. File names
nnnn comprises the name of the dataset. Maximum length is operating system dependent.
sss comprises the suffix used to designate the data type as follows:
|no suffix.||Elevation data.|
|fel||Pit filled elevation data.||produced by Fill pits and nondraining hollows|
|p||D8 drainage directions.||produced by D8 flow directions|
|sd8||D8 slopes.||produced by D8 flow directions|
|ad8||D8 contributing area’s, units are number of grid cells.||produced by D8 drainage area|
|slp||Dinf slopes.||produced by Dinf flow directions|
|ang||Dinf flow directions.||produced by Dinf flow directions|
|sca||Dinf contributing area, units are specific catchment area, i.e. number of grid cells times cell size.||produced by Dinf drainage area|
|plen||Longest path length to each grid point along D8 directions.||produced by Grid network order, Upslope total flow length, Upslope longest path length function|
|tlen||Total path length to each grid point along D8 directions.||produced by Grid network order, Upslope total flow length, Upslope longest path length function|
|gord||Strahler order for grid network defined from D8 flow directions.||produced by Grid network order, Upslope total flow length, Upslope longest path length function|
|src||Network mask based on channel source rules.||produced by RiverNetwork Raster|
|ord||Grid with Strahler order for mapped stream network.||produced by River Network Raster|
|w||Subbasins mapped using subbasinsetup.||produced Create Network and Sub-Watersheds|
|fdr||Flow directions enforced to follow the existing stream network||produced by Convert Connected Reach Network to Forced Flow Direction Grid|
|fdrn||Flow directions enforced to follow the existing stream network after cleaning to remove any loops||produced by flood|
The following files are used to represent channel networks.
Network connectivity file, nnnntree.dat.
This is essentially a list of links comprising a channel network. It is text with 7 columns as follows:
1 LINK NUMBERThis file is produced by the 'Create Network and Sub-Watersheds' command. The second and third columns refer to point coordinates, vectors along each link, from upstream to downstream, stored on the network coordinate, or 'coord.dat', file.
2 START POINT NUMBER IN COORD
3 END POINT NUMBER IN COORD
4 NEXT (DOWNSTREAM) LINK NUMBER IN CNET
5&6 PREVIOUS (UPSTREAM) LINK NUMBERS IN CNET
7 STRAHLER ORDER OF LINK IN CNET
Network coordinate file, nnnncoord.dat.
This is a list of coordinates defining the points along each channel link. It is text with 5 coulmns of data as follows:
1 X COORDINATE (metres)This file is produced by the 'Create Network and Sub-Watersheds' command. The coordinates are based on the coordinate system (and projection) implicit in the header bounding box information in the raster grid file. Coordinates are the centers of grid elements (pixels) corresponding to each channel network link. This file is only useful in conjunction with the 'tree' file which gives the start and end position (line or record) in this file of each channel network link.
2 Y "
3 DISTANCE ALONG CHANNELS TO GAUGE (metres or whatever units grid size is in)
4 ELEVATION (metres or whatever units the DEM is in)
5 CONTRIBUTING AREA (meter2 or whatever units grid size is in)
This is an open ESRI data format that stores vector data in DBF files. It is described in a white paper. TauDEM reads EPA reach files in Shape file format to enforce flow directions to follow existing streams where desired. TauDEM also outputs the delineated channel network and reach subwatersheds in Shape file format. The attribute table information associated with these shapefiles is as follows:
|LINKNO||Link Number. A unique number associated with each link (segmentof channel between junctions)|
|DSLINKNO||Link Number of the downstream link. -1 indicates that this does not exist.|
|USLINKNO1||Link Number of first upstream link|
|USLINKNO2||Link Number of second upstream link.|
|Order||Strahler Stream Order|
|Length||Length of the link|
|Magnitude||Shreve Magnitude of the link. This is the total number of sources upstream|
|DS_Cont_Ar||Drainage area at the downstream end of the link. Generally this is one grid cell upstream of the downstream end because the drainage area at the downstream end grid cell includes the area of the stream being joined.|
|Drop||Drop in elevation from the start to the end of the link|
|Slope||Average slope of the link (computed as drop/length)|
|Straight_L||Straight line distance from the start to the end of the link|
|US_Cont_Ar||Drainage area at the upstream end of the link|
|WSNO||Watershed number. Cross reference to the *w.shp and *w grid files giving the identification number of the watershed draining directly to the link.|
|DOUT_END||Distance to the outlet from the downstream end of the link|
|DOUT_START||Distance to the outlet from the upstream end of the link|
|DOUT_MID||Distance to the outlet from the midpoint of the link|
This is the first Graphic User Interface version. Older command line software may be accessed at http://www.engineering.usu.edu/dtarb/tardem.html.
Garbrecht, J. and L. W. Martz, (1997), "The Assignment of Drainage Direction Over Flat Surfaces in Raster Digital Elevation Models," Journal of Hydrology, 193: 204-213.
Jenson, S. K. and J. O. Domingue, (1988), "Extracting Topographic Structure from Digital Elevation Data for Geographic Information System Analysis," Photogrammetric Engineering and Remote Sensing, 54(11): 1593-1600.
Mark, D. M., (1988), "Network models in geomorphology," Chapter 4 in Modelling in Geomorphological Systems, Edited by M. G. Anderson, John Wiley., p.73-97.
Marks, D., J. Dozier and J. Frew, (1984), "Automated Basin Delineation From Digital Elevation Data," Geo. Processing, 2: 299-311.
Montgomery, D. R. and W. E. Dietrich, (1992), "Channel Initiation and the Problem of Landscape Scale," Science, 255: 826-830.
O'Callaghan, J. F. and D. M. Mark, (1984), "The Extraction of Drainage Networks From Digital Elevation Data," Computer Vision, Graphics and Image Processing, 28: 328-344.
Peckham, S. D., (1995), "Self-Similarity in the Three-Dimensional Geometry and Dynamics of Large River Basins," PhD Thesis, Program in Geophysics, University of Colorado.
Peuker, T. K. and D. H. Douglas, (1975), "Detection of surface-specific points by local parallel processing of discrete terrain elevation data," Comput. Graphics Image Process., 4: 375-387.
Tarboton, D. G., (1989), "The analysis of river basins and channel networks using digital terrain data," Sc.D. Thesis, M.I.T., Cambridge, MA, (Also available as Tarboton D. G., R. L. Bras and I. Rodriguez-Iturbe, (Same title), Technical report no 326, Ralph M. Parsons Laboratory for Water resources and Hydrodynamics, Department of Civil Engineering, M.I.T., September 1989).
Tarboton, D. G., R. L. Bras and I. Rodriguez-Iturbe, (1991), "On the Extraction of Channel Networks from Digital Elevation Data," Hydrologic Processes, 5(1): 81-100.
Tarboton, D. G., R. L. Bras and I. Rodriguez-Iturbe, (1992), "A Physical Basis for Drainage Density," Geomorphology, 5(1/2): 59-76.
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.
Tarboton, D. G. and U. Shankar, (1998), "The Identification and Mapping of Flow Networks from Digital Elevation Data," Invited Presentation at AGU Fall Meeting, San Francisco, December 6 to 10.
Tarboton, D. G. and D. P. Ames, (2001),"Advances in the mapping of flow
networks from digital elevation data," in World
Water and Environmental Resources Congress, Orlando, Florida, May 20-24,
ASCE. [ PDF