THE VICTORIA PROJECT, SRI-LANKA HYDROLOGICAL ANALYSIS FOR VICTORIA DAM

The hydrological analyses described in this Paper formed an important part of the studies for the Victoria Project of which the Victoria Dam is the major component. The purpose of the hydrological studies was t o provide consistent sets of river flow and climate data at the sites of the major components of the project, and to provide flood estimates for sizing the spillway and river diversion works. This Paper outline s the approach used in the overall study, and then concentrates on asp ects of specific relevance to the Victoria Dam. The main hydrological characteristics of the upper Mahaweli basin are presented as an introd uction to the overall water balance; the humid climate made the apprai sal of flow records relatively simple. Time series modelling was used to fill gaps in the observed flow records used for reservoir operation studies. The spillway design flood was based on the probable maximum precipitation (PMP) derived by maximizing a historic storm in which ra infall approaching the PMP covered most of the basin. Construction flo ods of moderate return period were estimated from a dimensionless anal ysis of regional flood records. The main lessons to be drawn are that water balance methods are of particular value in these humid monsoon c onditions, while the ratio of the PMP to the maximum recorded storm is lower than would be the case in more arid regions.