This model demonstrates the use of a recession constant applied to the operational volume in the reservoir to control discharges. The operational volume of the reservoir is calculated as the volume of water above a target water level. When the water level drops below this target, then there is no operational volume available to apply the recession constant and therefore the outflow request will be zero. When the water level rises above the target water level, the operational volume is positive and then we apply the recession constant to this value to calculate the withdrawal rate. The recession constant is in terms of %/day and when multiplied by the volume becomes a flow rate. This option is a good way to represent complex hydraulic controls in a simplistic way.
Below is a time history chart showing the water level compared to the target and the resulting inflow and reservoir discharges.