Lokalt omhändertagande av dagvatten i Västerås - Möjligheter till ökad användning i befintliga innerstadsområden
Local disposal of storm water i Västerås - possibilities for increased use in downtown areas
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 inthe vicinity of urban areas. Reduction of pollutants in storm water is a key action in order toprotect sensitive recipients and maintain high water quality. Storm water is traditionallytransported by storm sewers to the nearest recipient. In recent years the approach to stormwater management has changed; storm water should primarily be disposed of on site, throughlocal disposal of storm water, LOD. LOD is created by a combination of the function ofseveral smaller local facilities and the general sewer system. In LOD techniques like wet anddry ponds, ditches, rain gardens, infiltration areas and green roofs are used. The function of aLOD facility is reduction, equalization and delay of storm water flows. There are severaladvantages of LOD over traditional storm water management. The natural water balance isimitated, exposed water surfaces and green areas are perceived as aesthetically pleasing, areduction of pollutants occurs and the load on the grid is reducedThe aim of this work was to investigate the conditions and strategies for increased use ofLOD in existing urban areas in Västerås. This was done by examining two areas in Västeråscity center and by suggesting LOD solutions. Private land and public land has beendistinguished between for each area. The LOD plant is dimensioned so that the total outgoingflow is limited to 10 l / s, hectare. It has been investigated if the requirements for outboundflows from private property can be set lower and flows reduced by a further delay on publicland or if it is more advantageous to delay the flows individually. To simulate flow andmagazine volumes, the program StormTac has been used.The investigation has shown that storm water volumes to be disposed will be much lower ifthe disposal is done in one step. Available lawns should be used wherever possible toconstruct dry ponds, swales or other technics based on infiltration. By using lawns, largevolumes can be disposed, pollution is reduced effectively and the arrangement is relativelycheap. Rain gardens are more expensive to construct but provide an efficient cleaning ofstorm water and are nice from an aesthetic point of view. Rain gardens should be placedlengthwise along roads or pedestrian streets. With such a design, large storage volumes arecreated while the surrounding areas can still be used. The use of percolation basins areneeded when using LOD in urban paved areas. With the use of LOD plants, pollutants arereduced enough to reach the valuesand goals in Västerås? storm water plan.