Research papersThe temporal variability of a rainfall synthetic hyetograph for the dimensioning of stormwater retention tanks in small urban catchments

•Time distribution of rainfall has an influence on dimensioning of stormwater tanks.•Storm water tanks should be dimensioned for the most critical rainfall.•The most critical rainfall distribution is quadratic function y = a·x2.•Value of stormwater flow reduction coefficient affects the time of critical rainfall.

The paper presents issues relating to the influence of time distribution of rainfall on the required storage capacity of stormwater reservoirs. The research was based on data derived from simulations of existing drainage systems. The necessary models of catchments and the drainage system were prepared using the hydrodynamic modelling software SWMM 5.0 (Storm Water Management Model). The research results obtained were used to determine the critical rainfall distribution in time which required reserving the highest capacity of stormwater reservoir. In addition, it can be confirmed based on the research that dimensioning of enclosed structures should rely on using the critical precipitation generated as the characteristics of a synthetically developed rainfall vary dynamically in time. In the final part of the paper, the results of the analyses are compared and followed with the ensuing conclusions. The results of the research will have impact on the development of methodologies for dimensioning retention facilities in drainage systems.