Abstract

Over the last years, the City of Gdańsk suffers twice from flash floods. Both events were caused by intense storms which produced significant surface runoff and caused inundation private and cities properties. The first case of July 2001 flood [3], [9] was the turning point for the city authorities, who decide to look close on the flood management in small urban catchments. The aim of research projects was to establish technical solutions and procedures to be applied in case of risk of flooding due to heavy rain on all Radunia Channel tributaries. The largest basin is the catchment of the Oruński Stream. This area was recently intensely developed and according to the spatial planning the urbanisation process will proceed. The project’s closure took form of decisions concerning technical solutions modifying operation mode of Gdansk Water Junction System in order to ensure an optimal distribution of flood water. After 2003, Gdansk Floodway System rebuilding propositions started to be regularly implemented. Thanks to actions initiated in the river basin of Radunia channel, no more emergency situations were observed during the flood in 2016. In the paper, the hydrologic model of the water system of Oruński Stream will be presented with particular effort paid to the new and renovated retention structures. Hydrological modelling system of HEC HMS was used to simulate the basin response on precipitation. The 16,4 km2 model domain was divided into 35 sub-basins according to storm water drainage system. Both, current and proposed land use of the basin was taken into consideration. The operation of six existing and two proposed flood detention reservoirs were included in the simulations. The results showed the importance of reservoirs and water diversion structures on flood surge routing.

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