Time constants

The time constant for OL Drainage Inflow controls the rate of water entering the drain storage. The time constant for Outflow controls the rate of water draining to the destination. Thus, if the Outflow time constant is greater than the Inflow time constant, the drain storage will not accumulate any water. In this case, inflow to the drain will be instantly discharged to the destination.

The default values for both time constants is 0.001. This is quite high and will normally drain nearly all ponded water from the cell. Since the two time con­stants by default are the same, the default storage will be very low or zero. This will normally result in a very sharp peak in your streams in response to the instantaneous drainage of rainfall to the streams.

During model calibration, you can start decreasing the outflow time constant to dampen these drainage peaks.