The initial design of a soakaway may show that its outflow, combined with its storage, is in balance with its inflow and, therefore, works for the chosen design rainfall.

However, the soakaway must be capable of discharging from full to half-volume within 24 hours (default value) in readiness for a subsequent storm inflow of similar proportions.

The following calculation is incorporated within Soakaway Design to check the design

Half empty = ((Storage Volume) x 0.5) / (As50 x Soil Infiltration Rate) seconds


As50 = internal surface area of soakaway through which exfiltration can occur.