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185 lines
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HTML
185 lines
11 KiB
HTML
<html>
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<head><link rel="stylesheet" type="text/css" href="help.css"/></head>
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<body>
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<h1 class='module'>Stream Reach And Watershed</h1>
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<div class='author'>(c) 2010 by David G. Tarboton</div>
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<div class='description'>This tool produces a vector network and shapefile
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from the stream raster grid. The flow direction grid is used to connect
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flow paths along the stream raster. The Strahler order of each stream
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segment is computed. The subwatershed draining to each stream segment
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(reach) is also delineated and labeled with the value identifier that
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corresponds to the WSNO (watershed number) attribute in the Stream Reach
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Shapefile.</div>
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<div class='description'>This tool orders the stream network according to
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the Strahler ordering system. Streams that don't have any other streams
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draining in to them are order 1. When two stream reaches of different order
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join the order of the downstream reach is the order of the highest incoming
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reach. When two reaches of equal order join the downstream reach order is
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increased by 1. When more than two reaches join the downstream reach order
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is calculated as the maximum of the highest incoming reach order or the
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second highest incoming reach order + 1. This generalizes the common
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definition to cases where more than two reaches join at a point. The network
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topological connectivity is stored in the Stream Network Tree file, and
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coordinates and attributes from each grid cell along the network are stored
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in the Network Coordinates file.</div>
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<div class='description'>The stream raster grid is used as the source for
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the stream network, and the flow direction grid is used to trace connections
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within the stream network. Elevations and contributing area are used to
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determine the elevation and contributing area attributes in the network
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coordinate file. Points in the outlets shapefile are used to logically
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split stream reaches to facilitate representing watersheds upstream and
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downstream of monitoring points. The program uses the attribute field "id"
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in the outlets shapefile as identifiers in the Network Tree file. This tool
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then translates the text file vector network representation in the Network
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Tree and Coordinates files into a shapefile. Further attributes are also
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evaluated. The program has an option to delineate a single watershed by
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representing the entire area draining to the Stream Network as a single
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value in the output watershed grid.</div>
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<h2>Parameters</h2>
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<dl class='parameters'>
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<dt>Number of Processes <div class='type'>Integer</div></dt>
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<dd>The number of stripes that the domain will be divided into and the
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number of MPI parallel processes that will be spawned to evaluate each
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of the stripes.</dd>
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<dt>Pit Filled Elevation Grid <div class='type'>Raster Grid</div></dt>
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<dd>A grid of elevation values. This is usually the output of the "Pit
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Remove" tool, in which case it is elevations with pits removed.</dd>
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<dt>D8 Flow Direction Grid <div class='type'>Raster Grid</div></dt>
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<dd>A grid of D8 flow directions which are defined, for each cell, as
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the direction of the one of its eight adjacent or diagonal neighbors
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with the steepest downward slope. This grid can be obtained as the
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output of the "D8 Flow Directions" tool.</dd>
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<dt>D8 Drainage Area Grid <div class='type'>Raster Grid</div></dt>
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<dd>A grid giving the contributing area value in terms of the number
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of grid cells (or the summation of weights) for each cell taken as its
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own contribution plus the contribution from upslope neighbors that drain
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in to it using the D8 algorithm. This is usually the output of the "D8
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Contributing Area" tool and is used to determine the contributing
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area attribute in the Network Coordinate file.</dd>
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<dt>Stream Raster Grid <div class='type'>Raster Grid</div></dt>
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<dd>An indicator grid indicating streams, by using a grid cell value
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of 1 on streams and 0 off streams. Several of the "Stream Network
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Analysis" tools produce this type of grid. The Stream Raster Grid
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is used as the source for the stream network.</dd>
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<dt>Outlets Shapefile as Network Nodes <div class='type'>Point Shapefile (optional)</div></dt>
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<dd>A point shape file defining points of interest. If this file is used,
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the tool will only deliiniate the stream network upstream of these outlets.
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Additionally, points in the Outlets Shapefile are used to logically split
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stream reaches to facilitate representing watersheds upstream and downstream
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of monitoring points. This tool REQUIRES THAT THERE BE an integer attribute
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field "id" in the Outlets Shapefile, because the "id"
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values are used as identifiers in the Network Tree file.</dd>
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<dt>Delineate Single Watershed <div class='type'>Boolean</div></dt>
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<dd>This option causes the tool to delineate a single watershed by
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representing the entire area draining to the Stream Network as a single
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value in the output watershed grid. Otherwise a seperate watershed is
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delineated for each stream reach. Default is <strong>False</strong>
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(seperate watershed).</dd>
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</dl>
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<h2>Outputs</h2>
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<dl class='parameters'>
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<dt>Stream Order Grid <div class='type'>Raster Grid</div></dt>
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<dd>The Stream Order Grid has cells values of streams ordered according
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to the Strahler order system. The Strahler ordering system defines order
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1 streams as stream reaches that don't have any other reaches draining
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in to them. When two stream reaches of different order join the order
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of the downstream reach is the order of the highest incoming reach.
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When two reaches of equal order join the downstream reach order is
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increased by 1. When more than two reaches join the downstream reach
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order is calculated as the maximum of the highest incoming reach order
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or the second highest incoming reach order + 1. This generalizes the
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common definition to cases where more than two flow paths reaches
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join at a point.</dd>
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<dt>Watershed Grid <div class='type'>Raster Grid</div></dt>
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<dd>This output grid identified each reach watershed with a unique ID
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number, or in the case where the delineate single watershed option was
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checked, the entire area draining to the stream network is identified
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with a single ID.</dd>
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<dt>Stream Reach Shapefile <div class='type'>Polyline Shapefile</div></dt>
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<dd>This output is a polyline shapefile giving the links in a stream
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network. The columns in the attribute table are:
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<ul>
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<li>LINKNO — Link Number. A unique number associated with
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each link (segment of channel between junctions). This is arbitrary
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and will vary depending on number of processes used</li>
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<li>DSLINKNO — Link Number of the downstream link. -1
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indicates that this does not exist</li>
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<li>USLINKNO1 — Link Number of first upstream link. (-1
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indicates no link upstream, i.e. for a source link)</li>
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<li>USLINKNO2 — Link Number of second upstream link. (-1
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indicates no second link upstream, i.e. for a source link or an internal
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monitoring point where the reach is logically split but the network
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does not bifurcate)</li>
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<li>DSNODEID — Node identifier for node at downstream end
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of stream reach. This identifier corresponds to the "id"
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attribute from the Outlets shapefile used to designate nodes</li>
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<li>Order — Strahler Stream Order</li>
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<li>Length — Length of the link. The units are the horizontal
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map units of the underlying DEM grid</li>
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<li>Magnitude — Shreve Magnitude of the link. This is the
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total number of sources upstream</li>
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<li>DS_Cont_Ar — Drainage area at the downstream end of
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the link. Generally this is one grid cell upstream of the downstream
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end because the drainage area at the downstream end grid cell includes
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the area of the stream being joined</li>
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<li>Drop — Drop in elevation from the start to the end
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of the link</li>
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<li>Slope — Average slope of the link (computed as drop/length)</li>
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<li>Straight_L — Straight line distance from the start
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to the end of the link</li>
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<li>US_Cont_Ar — Drainage area at the upstream end of
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the link</li>
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<li>WSNO — Watershed number. Cross reference to the *w.shp
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and *w grid files giving the identification number of the watershed
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draining directly to the link</li>
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<li>DOUT_END — Distance to the eventual outlet (i.e. the
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most downstream point in the stream network) from the downstream end
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of the link</li>
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<li>DOUT_START — Distance to the eventual outlet from the
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upstream end of the link</li>
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<li>DOUT_MID — Distance to the eventual outlet from the
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midpoint of the link</li>
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</ul>
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</dd>
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<dt>Network Connectivity Tree <div class='type'>Text File</div></dt>
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<dd>This output is a text file that details the network topological
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connectivity is stored in the Stream Network Tree file. Columns are
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as follows:
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<ul>
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<li>Link Number (Arbitrary — will vary depending on number
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of processes used)</li>
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<li>Start Point Number in Network coordinates (*coord.dat) file (Indexed
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from 0)</li>
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<li>End Point Number in Network coordinates (*coord.dat) file (Indexed
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from 0)</li>
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<li>Next (Downstream) Link Number. Points to Link Number. -1 indicates
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no links downstream, i.e. a terminal link</li>
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<li>First Previous (Upstream) Link Number. Points to Link Number. -1
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indicates no upstream links</li>
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<li>Second Previous (Upstream) Link Numbers. Points to Link Number. -1
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indicates no upstream links. Where only one previous link is -1, it
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indicates an internal monitoring point where the reach is logically
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split, but the network does not bifurcate</li>
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<li>Strahler Order of Link</li>
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<li>Monitoring point identifier at downstream end of link. -1 indicates
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downstream end is not a monitoring point</li>
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<li>Network magnitude of the link, calculated as the number of upstream
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sources (following Shreve)</li>
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</ul>
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</dd>
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<dt>Network Coordinates <div class='type'>Text File</div></dt>
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<dd>This output is a text file that contains the coordinates and attributes
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of points along the stream network. Columns are as follows:
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<ul>
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<li>X coordinate</li>
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<li>Y Coordinate</li>
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<li>Distance along channels to the downstream end of a terminal link</li>
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<li>Elevation</li>
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<li>Contributing area</li>
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</ul>
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</dd>
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</dl>
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</body></html>
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