C.7 Infiltration Editor

The Infiltration Editor dialog is used to specify values for the parameters that describe the rate at which rainfall infiltrates into the upper soil zone in a subcatchment's pervious area. It is invoked when editing the Infiltration property of a subcatchment. The infiltration parameters depend on which infiltration model was selected for the project: Horton, Green-Ampt, or Curve Number. The choice of infiltration model can be made either by editing the project's Simulation Options or by changing the project's Default Properties.

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Green-Ampt Infiltration Parameters

The following data fields appear in the Infiltration Editor for Green-Ampt infiltration:

• Suction Head: Average value of soil capillary suction along the wetting front (inches or mm).

• Conductivity: Soil saturated hydraulic conductivity (in/hr or mm/hr).

• Initial Deficit: Fraction of soil volume that is initially dry (i.e., difference between soil porosity and initial moisture content). For a completely drained soil, it is the difference between the soil's porosity and its field capacity.

Horton Infiltration Parameters

The following data fields appear in the Infiltration Editor for Horton infiltration:

• Max. Infil. Rate: Maximum infiltration rate on the Horton curve (in/hr or mm/hr). Representative values are as follows:

• • • DRY soils (with little or no vegetation):
  • • Sandy soils: 5 in/hr

  • Loam soils: 3 in/hr

  • Clay soils: 1 in/hr

  • DRY soils (with dense vegetation):

  • • Multiply values in A. by 2

  • MOIST soils:

  • • Soils which have drained but not dried out (field capacity): Divide values from A and B by 3.

  • Soils close to saturation: Choose value close to min. infiltration rate.

  • Soils which have partially dried out: Divide values from A and B by 1.5 - 2.5. 

• Min. Infil. Rate: Minimum infiltration rate on the Horton curve (in/hr or mm/hr). Equivalent to the soil’s saturated hydraulic conductivity.

• Decay Const.: Infiltration rate decay constant for the Horton curve (1/hours). Typical values range between 2 and 7.

• Drying Time: Time in days for fully saturated soil to dry completely. Typical values range from 2 to 14 days.

• Max. Infil. Vol.: Maximum infiltration volume possible (inches or mm, 0 if not applicable). It can be estimated as the difference between a soil's porosity and its wilting point times the depth of the infiltration zone.

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Curve Number Infiltration Parameters

The following data fields appear in the Infiltration Editor for Curve Number infiltration:

• Curve Number: This is the SCS curve number which is tabulated in the publication SCS Urban Hydrology for Small Watersheds, 2nd Ed., (TR-55), June 1986. Consult the Curve Number Table for a listing of values by soil group, and the accompanying Soil Group Table for the definitions of the various groups.

• Conductivity: This property has been deprecated and is no longer used.

• Drying Time: The number of days it takes fully saturated soil to dry. Typical values range between 2 and 14 days.