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This article is aimed at defining the impact of the direction and velocity of waves of rainfall as they pass over interconnected stormwater detention tank systems. The simulations were conducted for a real urban catchment area as part of the Storm Water Management Model (SWMM) 5.1 programme. The results permit us to conclude that the direction and velocity of a moving wave of rainfall have a significant influence on the required volumes of interconnected stormwater detention tank systems. By comparing the modelling test results for stationary rainfall and rainfall moving over the urban catchment area, it has been demonstrated that differences in the required volume of the detention tank located at the terminal section of a stormwater drainage system are inversely proportional to the adopted value of the diameter of the outfall channel for upstream storage reservoirs. In extreme cases, the differences may be up to several dozen percentage points. Furthermore, it has been proven that the arrangement of the stormwater detention tanks in relation to one another and the adopted diameter of the outfall channel are key factors in identifying the degree to which the detention tanks are hydraulically dependent on one another.

In order to identify the most effective variants for reducing flood risk in cities and to provide protection for water resources, an in-depth study was carried out. The research results allowed for the identification of sustainable drainage infrastructure solutions that should be used to increase the efficiency of traditional drainage systems. The most effective solution turned out to be the simultaneous use of low impact development facilities and stormwater flow control devices in drainage systems (Variant IV). Applicationof this variant (maximum discharge QOmax = 246.39 dm3/s) allowed for the reduction of the peak flow by as much as 86% in relation to those values that were established in the traditional drainage system (maximum discharge QOmax = 1807.62 dm3/s). The use of Variant IV allowed for a combination of the advantages of low impact development (LID) facilities and stormwater flow control devices in drainage systems while limiting their disadvantages. In practice, the flow of rainwater from the catchment area to the drainage system was limited, the share of green areas increased, and the drainage system retention capacity grew. The proposed approach for reducing the increasing flood risk in cities and providing protection for water resources provides a structured approach to long-term urban drainage system planning and land use guidelines.

The paper presents an innovative retention canal for storm sewage as a competitive solution in relation to the ones currently used. The principle of operation of the retention canal, the conditions of its use in a sewage network and the basis for dimensioning were presented. To demonstrate its versatility and retention efficiency, comparative studies on the example of a drained catchment were carried out. A linear network layout composed of 12 storm canals with the retention reservoir located at the network outlet was assumed. Based on the developed algorithm, simulation tests were performed with the use of the SWMM 5.1 program. On the basis of hydrodynamic modelling it was determined: (1) the required geometry of storm canals, (2) the geometry of damming partitions and (3) the process of wastewater accumulation in the retention canal. Having the results of simulation research for rainfalls with a duration of 10 to 100 minutes, the critical rainfalls for network and retention canal dimensioning were determined. The comparison of hydrographs of sewage outflow from the examined catchment is interesting. From the value of 3.62 m3/s in the network it decreases three times to just 1.16 m3/s at the outlet of the retention canal. The retention canal with diameters identical to those established for the network, allow achieving the sewage retention capacity, which corresponds to a capacity of 1,844 m3 for a multi-chamber retention reservoir. Thus, the retention canal fully replaces the operation of a network of certain geometry and retention reservoir. The results of the research allowed the formulation of a number of important conclusions, including conclusions on cognitive significance. The critical rainfall appointed for the design of the retention canal always lasts longer than that, determined for the sewage network design. The retention canal is suitable for widespread use in the canals of new and already existing storm sewage systems and combined sewage systems.*

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