Lokal dagvattenhantering med grönytefaktorn
Sammanfattning: In cities hard surfaces prevent rainwater from infiltrating to the ground, which causes runoff,stormwater, that needs to be taken care of. With future changes in climate patterns winters in Scania, southern Sweden, will be warmer, with more rain and less snow and more days with more than 10 mm of precipitation. More intensive rains increase the chance of flooding of urban drainage systems. Open sewer systems and local stormwater treatment have become ways to combine stormwater treatment with green space in the cities. Best Management Practices (BMPs) are used within open sewer systems to retain, store and infiltrate precipitation. At the same time the Biotope Area Factor (or Green Area Factor) has become more commonly used as a method to improve the ecological situation of cities. It rates different categories of surfaces after ecological functions, among others, their ability to evapotranspirate, retain and infiltrate precipitation and stormwater. In this paper it is investigated whether the Biotope Area Factor can be used as an instrument to implement local stormwater treatment on private property in cities. The weightings (between 1,0 and 0,0)of the categories in the Biotope Area Factor developed in Malmö, Sweden in 1999 are compared with calculations on the same categories' ability to store, intercept and/or infiltrate precipitation from twenty storms with a frequency between 1 and 10 years and a duration between 1 and 24 hours. The results show that some of the weightings of the categories used in the Biotope Area Factor correspond to their calculated weightings, while other weightings are either overestimated or underestimated compared to their hydrological function. Using the Biotope Area Factor improves the surfaces' ability to store, intercept and/or infiltrate precipitation, yet for it to be used as an instrument to implement local stormwater treatment on private property in cities the weightings need to be modified to better correspond to the categories' hydrological function. The calculations should be based on design storms of a certain frequency and duration optimized to the peak flow capacity of the existing sewer system. The weightings need to be compiled with scientific methods and adjusted to local circumstances.
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