Page 11 - Water Pollution Management - Management Plans - Understanding your Risk

Step 5 Calculate the peak flow

Peak Flow Litres/Second

Peak flow (l/s) = Catchment area (Ha) x Run-off Factor x Return Period Factor

Return period 2 5 10 25 50

Factor 1 1.22 1.48 1.88 2.22

Note

The CIRIA Method does not take the slope of the site into account. For steep sites use the
MAFF Method.

The CIRIA method has a number of conservative assumptions built into it, has a tendency
to overestimate the peak flow.

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