Flood Studies Report

The Flood Studies Report, published in 1975, is used in relation to rainfall events in the United Kingdom. It has since been replaced by the Flood Estimation Handbook, but the method can still be used.
Calculation procedure.
It is possible to use the FSR to predict the depth of rainfall from a storm of a given duration and return period. The FSR includes values for two key variables mapped across the UK: the M5-60 minutes rainfall, and the ratio "r".
To find the depth of a rainfall of duration D and return period T at a given location in the UK, the following should be carried out:
Example.
Find the depth of rainfall from a storm of duration 6 hours and return period 10 years on a catchment of 5 km2 in Sheffield.
Therefore the expected depth of rainfall from the storm is 36.6mm. The mean intensity of rainfall is given by 36.6mm divided by 6 hours, which is 6.1mm/hour.
Storm profiles.
The above method is sufficient for finding the overall depth of rainfall during a storm. However, it is often useful from an engineering perspective to predict the intensity of rainfall during the storm, to allow structures such as drains and sewers to be designed with sufficient capacity for stormwater.
In general, the intensity of a storm is highest at the mid-duration point (known as the peak), and lowest at the start and end of the storm. Therefore, peaked profiles are applied to the storm data to provide a more realistic description of the rainfall intensity during the storm.
Flood Estimation Handbook.
The Flood Estimation Handbook was published in 1999 and replaces the FSR. It is based on the percentage runoff equation:
formula_1
where PR is percentage runoff, PIMP is percentage imperviousness of the catchment, SOIL is the soil index and UCWI is urban catchment wetness index.