Option

Description

Effective impervious area factor - IF

The ratio of impervious to pervious ground on the site.

Porosity factor - PF (mm)

A factor representing how porous the ground is.

New antecedent precipitation index (NAPI) calculations

Decay factor - C

Determines how much fallen rain from previous day affects the runoff factor.

Daily evaporation - E (mm/day)

The amount of water that evaporates each day.

NAPI calculation mode

Specify whether to enter data manually, or to automatically calculate it by entering the amount of rain experienced for each day for the 30 days prior to the storm event.

Selecting Automatic enables the graph and grid, and disables the manual entering of the NAPI.

The NAPI is calculated from the data in the grid and the graph is a graphical representation of the grid values.

NAPI

30 day antecedent precipitation index.