In planning and developing multipurpose reservoirs it is necessary to make an allocation of storage space for sediment accumulation. This sediment accumulation, in turn, influences the design of the dam because of its effect on active storage capacity requirements, outlet sill elevations, recreational facilities, and backwater conditions. Therefore, it is necessary to predict the probable distribution of the sediment in the reservoir with time. Two methods of predicting the probable sediment distribution are given and an example shown. One method is basically mathematical (area-increment method), whereas the other is a mathematical procedure developed on the basis of actual experiences (empirical area-reduction method). The area in which additional study is needed to evolve procedures that will give consistently reliable predictions of sediment distribution under varying conditions is described.