Work reported here consists of two parts: the first part describes studies performed on a conceptual catchment, the second part, presented as a separate paper, describes studies on real catchments in the city of Lund (Niemczynowicz 1984b).

In this paper we try to find the general shape of the relation between storm movement parameters like storm duration, intensity, velocity and direction, and its influence on peak discharge. This influence is called a “directional bias”. Different factors affecting the magnitude of directional bias are described. The relations between rainfall characteristics and the magnitude of the directional bias are shown for a conceptual catchment.

The most important conclusion is that the maximal directional bias can theoretically reach values of several hundred percent, but this can happen only in a catchment with specially designed linear geometry. Maximal directional bias can be expected for storms moving downstream the catchment with velocity equal to the average flow velocity. Maximal directional bias occurs for storms with short duration giving low peak discharge, which are not important for design purposes.