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Each Stormwater Control has an associated sizing calculator that allows the user to either:

(a) specify a new volume for the Stormwater Control whilst varying a chosen dimension, e.g. Depth, Width, Length etc.

(b) specify a scale factor to modify the existing volume of the Stormwater Control, again whilst varying a chosen dimension

(c) in the case of a Tank or Pond to specify a particular side slope, either from its top downwards or base upwards

<screenshot of the SWC sizing calculator (can be from any of the SWC types)>

The SWC sizing calculator consists of the following options:


Choose Volume or Runoff Reduction Volume to specify a volume. When choosing either of these a calculator button appears to the right; if Volume was chosen then clicking on the calculator button produces the Quick Storage Estimate (QSE) calculator, if Rural Reduction Volume is chosen then clicking on the calculator button produces the Water Quality Volume (WQv) calculator. Using either of these calculators will return a volume into the sizing calculator; In the case of the QSE calculator the returned volume is the centre of the estimated storage volume range. In the case the WQv calculator the returned volume is the Target Volume stated in the WQv's report.

Choose Scale to specify a change in scale of the current Total Volume of the SWC (as given in the bottom right of the SWC's Properties form). The figure entered is relative, so 0% is no change in Total Volume, 100% is a doubling in Total Volume, -50% results in halving in Total Volume.

For Tank and Pond SWCs there is a third option: Side Slope. Choose this option to impose a side slope to the structure of the Tank or Pond, specifying the side slope in the field below. In addition the third row of the form is changed to Maintain whose combo box contains two options: Top Area and Base Area. Choose Top Area to impose the side slope from the top area downwards; choose Base Area to impose the side slope from the base area upwards.

Update (for all Methods except Side Slope - relevant to Tank and Pond SWCs only)

Choose a parameter that is to be updated when the SWC is resized to the new volume. This list is specific to the type of SWC.


Bioretention Calculators











Porous Paving (with and without Underdrain)

Infiltration Trench