Area inflows can be applied to the system using the Area Inflow type.



An area can be entered directly or calculated automatically from the polygon drawn on the Plan. 

Preliminary Sizing

The Area, Volumetric Runoff Coefficient, Percent Impervious and Time of Concentration values shown in the preliminary Sizing tab will be used for initial sizing of pipes and stormwater controls using Rational Method style calculations.

If these values are not entered here, the default values or the values from the current dynamic sizing runoff method will be used.

Volumetric Runoff Coefficients

Used to factor the runoff when the Time Area Diagram or Time of Concentration Runoff Methods are selected. If a UK Rainfall pattern ( FSR Rainfall /  FEH Rainfall) is selected in the Analysis Criteria, values can instead be specified seasonally. The CVs specified will be used for the Summer and Winter storm analysis, if that type of storm is enabled in the Select Rainfall section within the Analysis Criteria.

Runoff Coefficient Calculator is available which allows the Volumetric Runoff Coefficient to be calculated from Land Use and Overland Slope.

Runoff Method

The preferred runoff methods can be selected - select from the methods below for details and required input parameters.

Time of Concentration


Santa Barbara Urban Hydrograph


Time Area Diagram

FSR Unit Hydrograph

FEH Unit Hydrograph

ReFH Unit Hydrograph

ReFH2 Unit Hydrograph

Simplified Modified Rational Method

Green Roof Runoff Method