Low flow analysis for the blue Nile river

Two mathematical models were developed to investigate the low flows of the blue Nile river at a single site (Eldeim station - Sudan). The first model evaluates the frequency of annual minimum flow (annual minimum series model). To develop such a model, the performance of 13 flow frequency procedures formulated by the combination of 5 distribution functions and 3 methods of parameters estimation were examined. The results have shown that out of these procedures, three can be used in low flow magnitude estimation, among which extreme value type 1 (EV1) associated with the method of maximum likelihood performs best. The second model which simulates the drought volume corresponding to some specific demand levels, was developed using mass curve analysis technique. The required reservoir capacities, were calculated at yield levels of 10, 20, 25 and 30 percent of the mean flow. The results have shown that for such small demand levels, simplest drought which consists of a single deficit followed by a surplus greater than it, were encountered. High demand levels should be considered in the future studies.