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| To compute the time of concentration in a sub-basin, the longest flow path in each basin must be defined. Once a watershed has been defined and broken into sub-basins, flow path arcs ([[WMS:Time Computation|Time Computation arcs]]) may be defined for each sub-basin. These arcs must be created in a [[WMS:Time Computation|Time Computation Coverage]]; the [[WMS:Coverages|Coverages]] dialog in WMS includes the option to create this type of coverage. The new coverage should be created and activated before creating flow path arcs.
| | #REDIRECT [[WMS:Time Computation]] |
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| When a Time Computation Coverage is active, Tc arcs may be created using the Create Feature Arc tool in the Map Module of WMS. These paths are created by simply pointing and clicking along the desired path, and double-clicking to end the arc. The Tc arcs created should start near the basin outlet and follow the longest flow path in the basin. This path must often be determined from knowledge of the area or visual inspection of a map or photograph of the area. However, WMS can automatically create flow paths if elevation data exists and is imported into WMS. By creating a node at the furthest point in the basin, the user can direct WMS to define the flow path to the outlet when the [[WMS:Flow Paths to Time Computation Arcs|Node to Flow Path]] command is issued from the '''Feature Objects''' menu.
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| '''NOTE:''' the flow path arc for each basin must not cross the basin boundary at any point. Such a crossing will result in errors.
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| ==Related Topics==
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| * [[WMS:Compute Regression Tc|Compute Regression Tc]]
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| * [[WMS:Assigning the Regression Equation|Assigning the Regression Equation]]
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| * [[WMS:Regression Tc Arc Computations|Regression Tc Arc Computations]]
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| * [[WMS:Automated Tc Calculations|Automated Tc Calculations]]
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| {{WMSMain}}
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