DESIGN STORM STUDIES FOR THE UPPER KRISHNA RIVER CATCHMENT UPSTREAM OF THE ALMATTI DAM SITE

The Almatti dam is the major engineering feature in the development of water resources in the Upper Krishna river forming a storage reservoi r of 6425 million m(3) at spillway crest level. In this paper, the des ign storm rainfalls for different return periods and also the Probable Maximum Precipitation (PMP) for the catchment above Almatti dam have been estimated to review the adequacy of the flood spillway design for the dam. The design storm rainfalls of various return periods have be en computed from a statistical analysis of point and areal time series of annual maximum rainfall. In evaluating the PMP, the maximum observ ed rainfall obtained by Depth Duration method were maximized as the or ography of the Western Ghats plays profound influence over the catchme nt. It was found that (area 35925 km(2)) the highest areal rainfalls o ver the catchment were 14.0 cm, 21.5 cm and 24.6 cm in 1, 2 and 3-day durations, respectively. These are scaled up by a factor of 1.23 to ob tain the PMP rainfalls. The areal PMP estimates for the upper Krishna River (UKR) catchment above Almatti dam have been found to be 18.0 cm, 27.0 cm and 31.0 cm, respectively.