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Sammanfattning

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.