CN/Runoff Coefficient Lookup Dialog

The CN/Runoff Coefficient Lookup dialog is used as part of the process of generating SCS Runoff Curve Numbers or SRM Runoff Coefficients from GIS data on land use and soil type. The dialog is displayed when Subcatchment | CN/Runoff Coefficient Dialog lookup is selected from the Model menu.

The process requires two GIS files (land use and soil type), which can be loaded as GIS background layers, and a lookup table that relates these to Curve Number.

For further information, see the Setting Runoff Coefficients from GIS Data topic.

Option Description
Parameter

Select the type of value to be set:
GIS Surface Import

Select the source of the Land Use and Soil Type data:

  • From Files - browse for the Land Use/Soil Type files using the button
  • From Layers - select the GIS layer to be used from the Land Use/Soil Type dropdown

Use the Field dropdown to select the field in the GIS file that contains the Land Use/Soil Type data.
Lookup Table

Enter the path of the csv format lookup table, or browse for the table using the .button.

Number of Soil Types - the total number of lookup columns (ignoring the Land Use values in column 1).
Update selected subcatchments only

Check this option to set values for currently selected subcatchments only.

If this option is unchecked, values will be set for all subcatchments in the network for which data is available.
Flag Identifier

Flag to be applied to changed data.

Select an existing flag from the dropdown list or click the New Flag button to display the User Defined Flags Dialog.
If input data contains invalid geometry

Select option for action to carry out if GIS data contains invalid geometry:

  • Ignore and continue - continue update process if land use/soil type polygons contain invalid geometry
  • Stop and report - stop update process and display log if GIS data polygons contain invalid geometry
Log

Set the log display options:

  • Display - check this box to display a log of the calculation process after values have been updated.
  • Summary Table - enabled when Display option is selected. Check this box to include summary statistics for each updated subcatchment in the process log.
  • Lookup Table - enabled when Display option is selected. Check this box to include lookup table details in the process log.

Setting Runoff Coefficients from GIS Data

SCS Model

Simple Runoff Model (SRM)