Urban surface runoff under simulated heavy rainfalls

In the face of ongoing climate change, changes in precipitation patterns are observed. More and more often, rainfall is characterized by high intensity and short duration. Such rainfall poses a threat to urban areas as it may generate urban flash floods. As a result of intense rainfall on impermeable surfaces, surface runoff accumulates and the capacity of the storm sewer system is exceeded. The aim of the presented research was to identify the dynamics of surface runoff depending on the rainfall intensity, type of land cover and soil moisture conditions. It was carried out as a series of field experiments with a rainfall simulator.

The experiment was conducted at the research station located in the Różany Strumień catchment (Poznań, Poland). The station consists of 4 plots (20 x 1 m each), with different land cover: black fallow, grass, concrete paver blocks and an impermeable testing plot. The program of experiments included seven types of precipitation, corresponding to the classification of Chomicz from A0 (strong rain, intensity 4 mm∙h^-1, duration 360 min) to B2 (torrential rain, intensity 60 mm∙h^-1, duration 70 min). Each rainfall was simulated twice in dry and wet ground conditions. The experiment was carried out in July 2022.

The result of field research is 56 surface runoff dynamics curves depending on: type of land cover, precipitation category according to Chomicz and soil moisture conditions. On the basis of curves obtained from the experiments, four new descriptors were determined, characterizing the variability of surface runoff in urbanized areas: volume of surface runoff, runoff coefficient, the moment of runoff initiation and runoff dynamics coefficient.