Is there a place for regional coefficients in the UK?

Abstract

In many parts of the world, it is common to estimate the value of extreme floods using regional coefficients such as those of Creager or Francou–Rodier. It seems that these methods have not hitherto been applied in the UK and this paper examines whether they could play a useful role for preliminary flood estimates or for checking existing estimates and comparing them with those made by more sophisticated methods for similar catchments. The method is extremely rapid and can be applied in a few minutes by those familiar with it. However, it appears to have limited usefulness for UK, although it does have potential for highlighting cases where peak reservoir inflows are surprisingly high or low. For projects overseas the authors are aware of instances where the use of regional coefficients has been instrumental in flagging up major errors in the proposed size of spillways – both for spillways planned to be too big and expensive and for others where the planned capacity was too small. In such cases, the planned capacity has been re-examined by other methods and appropriate amendments were made. Where there are few river flow data available, regional coefficients are sometimes used for the design.