A time of concentration may be defined for the impervious and pervious portions of the catchment separately. This options window has three main areas:

All the information on the retarding basin or on-site storage at a selected node can be manipulated using the appropriate buttons on the Retarding Basin Window.

Basin Invert Datum Level

Level of outlet conduit invert at entrance. This level is used to tie ALL interconnected basins together, and is the datum level for levels in the basin level-storage, level-discharge, and level-tailwater relations, (i.e. the Level curves must start with a value of 0.0 or equal to the Basin Invert Datum).

Spillway Depth

Depth of water below the normal spillway sill, in metres. This value is only required if the Normal Spillway checkbox is on.