A generalised technique for the estimation of probable maximum precipitation in India

Abstract

In this paper a version of a generalised method of estimating probable maximum precipitation (PMP) is applied to the catchments of four large dams in India. The value of a secure dam is high both in terms of human life and in economic terms. Reliable estimates of PMP are required in estimating the design flood for spillways of large earth and rockfill dams. Estimates of PMP obtained using the traditional method of moisture maximisation and storm transposition can be unreliable as highly efficient rain storms may not be represented in the rainfall records of an area. Generalised methods of (calculating) PMP are used to obtain reliable estimates of PMP and also to give estimates which are consistent over a region. This is done by pooling together all the rainfall data from a very large area. The rainfall depths are normalised for such factors as storm dew-point temperature, distance of the storm from the coast, topographic effects and any intervening mountain barriers between the rainfall area and the moisture source. These normalised values can then be applied to any individual catchment, with the appropriate adjustment factors.