How Big a Soakaway???
Assuming the trial pit has proved suitable, the next task is to calculate the size of soakaway that will be required. There are a few formulae used to calculate the required storage capacity for a soakaway, but the one we normally use is… Vol = A × (rainfall rate/3000) This formula states that the volume of soakaway required is equal to the area to be drained (in m²) multiplied by the product of the storm rainfall rate (assumed to be 50mm/hr in UK) divided by 3000. For example:- Area to be drained = 60m², hence, Volume required = 60 × (50/3000) = 1m³ Note that this is the storage volume required between the dry base or water table level of the soakaway, and the invert (inlet) level of the incoming drainage pipe, and assumes that the chamber is empty, not filled with old bricks, lumps of concrete or gravel, etc., as is often found in older soakaways. If the chamber were to be filled with, say, a gravel, this would significantly reduce the storage volume, requiring a much bigger chambe
