WMS:MODRAT Tc Coverage Type

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Use this type of coverage to define time of concentration arcs for a MODRAT simulation.

To change the attributes for feature arcs, select the arc(s) and click Attributes from the Feature Objects menu, or double-click on the arc. Feature arcs created in the Modrat Tc coverage can have the following conveyance types.

  • street
  • 1/2 street
  • pipe
  • channel
  • mountain channel
  • valley channel
  • triangular channel
  • overland
  • none

Conveyances are the links within a hydrologic model that simulate the flow of water through channel reaches. A hydrograph is specified at the top of a reach and a resulting outflow hydrograph is calculated at the bottom. Conveyance modeling is necessary due to the reduction of peak flow rates by attenuation and travel time. These processes affect the hydrograph at the downstream end of the conveyances.

The type of conveyance is important because water will flow much faster in a pipe than through a valley. The length and slope of the conveyance between collection points are also important in determining the effects of hydrologic routing. The conveyance lengths are determined by measuring the flow path length using a scale or GIS. This length information is combined with the elevation data from a DEM or topographic map to determine the slope.

Further conveyance setting are entered in the model parameters.

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