| Summary: | The construction of buildings and paved surfaces changes the natural water balance. Precipitation generates surface runoff and storm water instead of infiltrating into the soil. Storm water has come to be considered as a major source of pollution in lakes and streams in the vicinity of urban areas. Reduction of pollutants in storm water is a key action in order to protect sensitive recipients and maintain high water quality. Storm water is traditionally transported by storm sewers to the nearest recipient. In recent years the approach to storm water management has changed; storm water should primarily be disposed of on site, through local disposal of storm water, LOD. LOD is created by a combination of the function of several smaller local facilities and the general sewer system. In LOD techniques like wet and dry ponds, ditches, rain gardens, infiltration areas and green roofs are used. The function of a LOD facility is reduction, equalization and delay of storm water flows. There are several advantages of LOD over traditional storm water management. The natural water balance is imitated, exposed water surfaces and green areas are perceived as aesthetically pleasing, a reduction of pollutants occurs and the load on the grid is reduced The aim of this work was to investigate the conditions and strategies for increased use of LOD in existing urban areas in Västerås. This was done by examining two areas in Västerås city center and by suggesting LOD solutions. Private land and public land has been distinguished between for each area. The LOD plant is dimensioned so that the total outgoing flow is limited to 10 l / s, hectare. It has been investigated if the requirements for outbound flows from private property can be set lower and flows reduced by a further delay on public land or if it is more advantageous to delay the flows individually. To simulate flow and magazine volumes, the program StormTac has been used. The investigation has shown that storm water volumes to be disposed will be much lower if the disposal is done in one step. Available lawns should be used wherever possible to construct dry ponds, swales or other technics based on infiltration. By using lawns, large volumes can be disposed, pollution is reduced effectively and the arrangement is relatively cheap. Rain gardens are more expensive to construct but provide an efficient cleaning of storm water and are nice from an aesthetic point of view. Rain gardens should be placed lengthwise along roads or pedestrian streets. With such a design, large storage volumes are created while the surrounding areas can still be used. The use of percolation basins are needed when using LOD in urban paved areas. With the use of LOD plants, pollutants are reduced enough to reach the values and goals in Västerås’ storm water plan.
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