Derived Distribution for Estimation of Snowmelt Flood Frequency in an Ungauged Basin

A.N. Gelfan

A compositional method for calculating the probability distribution function for the layer of snowmelt runoff based on the distribution of maximum snow reserves and indicators on the absorption capability of catchments, with the aid of the runoff’s dependence on this factors, which are territorially common to European Russia. An expression is derived that combines the probability of an excess of the runoff layer, the parameters of the dependence, and statistical characteristics of the factors of runoff formation. A method is described for finding the territorially common parameters of the obtained distribution with the aid of observations data at the small catchments of the Nizhnedevitskaya and Pridesnyanskaya water-balance stations. The compositional method is applied for calculating the curves for the supply of the floodwater layer in the Sosna and Seim rivers; it has given satisfactory results without the need for observations data of the runoff of these rivers.