Available Air Space - The available air space is the volume of allotment tank space between the orifice outlet and the spillway sill. (m³/lot).

Available Water Space - The available water space is the volume of allotment tank space below the orifice outlet invert (m³/lot).

Roof Capture - This represents the percentage of allotment roof area directed into the water tank (%).

Outlet Discharge - This is the discharge from the orifice in the side of the water tank with a driving head equal to TWHT (m).

Height Outlet to Spill - This is the height between the invert of the orifice outlet and the sill of the spillway at the top of the tank (m).

Spill Width - Width of spillway (m).

HED - Check if the outlet orifice can be controlled by a high early discharge.