Option

Description

Time of Concentration (hours)

The time it takes for a drop of water to travel from the most distant part of the catchment to the catchpit. Click ... to display the Time of Concentration calculator.

User Specified Point Rainfall

Select this option if the Rational Runoff calculations must not calculate the Point Rainfall value from the standard Rational Runoff graphs, but must make use of the entered value.

Rural Percentage

The rural portion of the catchment area expressed as a percentage of the total area.

Rural Factor

The rural area runoff coefficient, which can be calculated using the rural coefficient calculator.

Urban Percentage

The urban portion of the catchment area expressed as a percentage of the total area.

Urban Factor

The urban area runoff coefficient, which can be calculated using the urban coefficient calculator.

Lake Percentage

The percentage of the catchment area consisting of lakes or ponds, which do not contribute to runoff.