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73 lines
4.2 KiB
HTML
73 lines
4.2 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'>D-Infinity Decaying Accumulation</h1>
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<div class='author'>(c) 2010 by David G. Tarboton</div>
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<div class='description'>The D-Infinity Decaying Accumulation tool creates
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a grid of the accumulated quantity at each location in the domain where
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the quantity accumulates with the D-infinity flow field, but is subject
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to first order decay in moving from cell to cell. By default, the quantity
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contribution of each grid cell is the cell length to give a per unit width
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accumulation, but can optionally be expressed with a weight grid. The decay
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multiplier grid gives the fractional (first order) reduction in quantity
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in accumulating from grid cell <tt>x</tt> to the next downslope cell.</div>
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<div class='description'>A decayed accumulation operator <tt>DA[.]</tt>
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takes as input a mass loading field <tt>m(x)</tt> expressed at each grid
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location as <tt>m(i, j)</tt> that is assumed to move with the flow field
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but is subject to first order decay in moving from cell to cell. The output
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is the accumulated mass at each location <tt>DA(x)</tt>. The accumulation
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of <tt>m</tt> at each grid cell can be numerically evaluated.</div>
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<p align="center"><img src="img/decayeqn.gif"></img></p>
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<div class='description'>Here <tt>d(x) = d(i ,j)</tt> is a decay multiplier
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giving the fractional (first order) reduction in mass in moving from grid
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cell <tt>x</tt> to the next downslope cell. If travel (or residence) times
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<tt>t(x)</tt> associated with flow between cells are available <tt>d(x)</tt>
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may be evaluated as <tt>exp(-k t(x))</tt> where <tt>k</tt> is a first order
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decay parameter. The weight grid is used to represent the mass loading <tt>m(x)</tt>.
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If not specified this is taken as 1. If the outlets shapefile is used the
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function is only evaluated on that part of the domain that contributes flow
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to the locations given by the shapefile.</div>
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<p align="center"><img src="img/decay.gif"></img></p>
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<div class='description'>Useful for a tracking contaminant or compound
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subject to decay or attenuation.</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>D-Infinity Flow Direction Grid <div class='type'>Raster Grid</div></dt>
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<dd>A grid giving flow direction by the D-infinity method. Flow direction
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is measured in radians, counter clockwise from east. This grid can be
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created by the function "D-Infinity Flow Directions".</dd>
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<dt>Decay Multiplier Grid <div class='type'>Raster Grid</div></dt>
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<dd>A grid giving the factor by which flow leaving each grid cell is
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multiplied before accumulation on downslope grid cells. This may be
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used to simulate the movement of an attenuating substance.</dd>
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<dt>Weight Grid <div class='type'>Raster Grid (optional)</div></dt>
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<dd>A grid giving weights (loadings) to be used in the accumulation.
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If this optional grid is not specified, weights are taken as the linear
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grid cell size to give a per unit width accumulation.</dd>
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<dt>Outlets Shapefile <div class='type'>Point Shapefile (optional)</div></dt>
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<dd>This optional input is a point shapefile defining outlets of interest.
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If this file is used, the tool will only evaluate ther area upslope of
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these outlets.</dd>
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<dt>Check for edge contamination <div class='type'>Boolean</div></dt>
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<dd>This option determines whether the tool should check for edge
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contamination. Edge contamination is defined as the possibility that
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a value may be underestimated due to grid cells outside of the domain
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not being considered when determining contributing area. Default
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<strong>True</strong>.</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>Decayed Specific Catchment Area Grid <div class='type'>Raster Grid</div></dt>
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<dd>The D-Infinity Decaying Accumulation tool creates a grid of the
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accumulated mass at each location in the domain where mass moves with
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the D-infinity flow field, but is subject to first order decay in moving
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from cell to cell.</dd>
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</dl>
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</body></html>
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