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101 lines
6.1 KiB
HTML
101 lines
6.1 KiB
HTML
<html>
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<head><link rel="stylesheet" type="text/css" href="help.css"/></head>
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<h1 class='module'>D-Infinity Concentration Limited Acccumulation</h1>
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<div class='author'>(c) 2010 by David G. Tarboton</div>
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<div class='description'>This function applies to the situation where an
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unlimited supply of a substance is loaded into flow at a concentration or
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solubility threshold Csol over a region indicated by an indicator grid (dg).
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It a grid of the concentration of a substance at each location in the domain,
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where the supply of substance from a supply area is loaded into the flow
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at a concentration or solubility threshold. The flow is first calculated
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as a D-infinity weighted contributing area of an input Effective Runoff
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Weight Grid (notionally excess precipitation). The concentation of substance
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over the supply area (indicator grid) is at the concentration threshold.
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As the substance moves downslope with the D-infinity flow field, it is
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subject to first order decay in moving from cell to cell as well as dilution
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due to changes in flow. The decay multiplier grid gives the fractional
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(first order) reduction in quantity in moving from grid cell <tt>x</tt>
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to the next downslope cell. If the outlets shapefile is used, the tool
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only evaluates the part of the domain that contributes flow to the locations
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given by the shapefile. This is useful for a tracking a contaminant or
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compound from an area with unlimited supply of that compound that is
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loaded into a flow at a concentration or solubility threshold over a zone
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and flow from the zone may be subject to decay or attenuation.</div>
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<div class='description'>The indicator grid (<tt>dg</tt>) is used to delineate
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the area of the substance supply using the (0, 1) indicator function <tt>i(x)</tt>.
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<tt>A[]</tt> denotes the weighted accumulation operator evaluated using
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the D-Infinity Contributing Area function. The Effective Runoff Weight
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Grid gives the supply to the flow (e.g. the excess rainfall if this is
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overland flow) denoted as <tt>w(x)</tt>. The specific discharge is then
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given by:</div>
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<pre align="center">Q(x)=A[w(x)].</pre>
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<div class='description'>This weighted accumulation <tt>Q(x)</tt> is output
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as the Overland Flow Specific Discharge Grid. Over the substance supply area
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concentration is at the threshold (the threshold is a saturation or solubility
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limit). If <tt>i(x) = 1</tt>, then</div>
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<pre align="center">C(x) = Csol, and L(x) = Csol Q(x),</pre>
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<div class='description'>where <tt>L(x)</tt> denotes the load being carried
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by the flow. At remaining locations, the load is determined by load accumulation
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and the concentration by dilution:</div>
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<p align="center"><img src="img/claeqn.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 Concentration grid output is <tt>C(x)</tt>. If the
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outlets shapefile is used, the tool only evaluates the part of the domain
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that contributes flow to the locations given by the shapefile.</div>
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<p align="center"><img src="img/clafig.gif"></img></p>
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<div class='description'>Useful for a tracking a contaminant released or
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partitioned to flow at a fixed threshold concentration.</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>Disturbance Indicator Grid <div class='type'>Raster Grid (optional)</div></dt>
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<dd>A grid that indicates the source zone of the area of substance
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supply and must be 1 inside the zone and 0 or "no data" over
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the rest of the domain.</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 or decaying substance.
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If travel (or residence) times <tt>t(x)</tt> associated with flow between
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cells are available <tt>d(x)</tt> may be evaluated as <tt>exp(-k t(x))</tt>
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where <tt>k</tt> is a first order decay parameter.</dd>
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<dt>Effective Runoff Weight Grid <div class='type'>Raster Grid</div></dt>
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<dd>A grid giving the input quantity (notionally effective runoff or
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excess precipitation) to be used in the D-infinity weighted contributing
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area evaluation of Overland Flow Specific Discharge.</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 the area upslope of
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these outlets.</dd>
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<dt>Concentration Threshold <div class='type'>Double</div></dt>
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<dd>The concentration or solubility threshold. Over the substance supply
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area, concentration is at this threshold. Default <strong>1.0</strong>.</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>Concentration Grid <div class='type'>Raster Grid</div></dt>
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<dd>A grid giving the resulting concentration of the compound of interest
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in the flow.</dd>
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</dl>
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</body></html>
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