Point and areal PMP estimates for durations of two and three days in India

Abstract

The risk of dam failure in India, coupled with better analysis of extreme storm events, has led to the estimation of revised one-day probable maximum precipitation (PMP). For some water conservation projects where the catchment area is very large, there is a need to have estimates of PMP for durations of both two and three days. These are provided in this paper. It was found that the two-day PMP over the Indian region varied from 100 cm over the central peninsula to over 290 cm in eastern India. For a duration of three days the corresponding values are 120 cm and 370 cm. For water management projects which include impounding reservoirs, an estimate has been made of the probable maximum flood (PMF) based on the new PMP estimates. The results of the design flood estimates were compared with existing estimates at the same sites and in most cases were found to be considerably higher. A comparison of the revised estimates of PMF and recorded floods in India shows that the trend of the rates of runoff in relation to catchment area differ by an average of 38% for an area of 1000 km² and 46% for an area of 10 000 km². These results show that some dams in India may be unsafe in the event of the probable maximum flood.