WMS:OC Rational Sub-area Data

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Orange County Rational Method – Edit Parameters dialog

When setting up a Orange County Rational Method simulation, data must be entered for each sub-area.

  • Area – The sub-area area (acres or ha.) can be automatically computed when using a DEM or TIN
  • % Nonmountainous and % Mountainous – The percentage of the sub-area that lies below and above 2000 ft, respectively.

Use the Compute % Mountainous button to calculate these values using a DEM or TIN.

Initial Sub-area

  • Tc – The time of concentration (min)
  • Intensity – The rainfall intensity (in/hr) is automatically computed based on the Tc


  • ap – Pervious area percentage
  • Fp – Pervious area loss rate
  • Fm – Maximum area loss rate

Calculate Fm by toggling on the Compute Fm checkbox, entering values for ap and Fp, and using the Compute Fm button or click on the Compute Fm – GIS button to use GIS data.

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