GIS-BASED FLOOD RISK ASSESSMENT FOR SUSTAINABLE STORMWATER MANAGEMENT IN HAMMARÖ MUNICIPALITY : A case study based on a multicriteria approach

Sammanfattning

Sustainable management of urban stormwaters has become increasingly important in relation to climate change, as it reduces damage to critical infrastructure, private property and ecosystems. Extreme weather events, such as heavy precipitation, are occurring more frequently and are projected to increase further in both frequency and intensity due to global warming. At the same time, urban densification and expansion of impervious surfaces alter functions of the hydrological cycle, impairing natural drainage processes and increasing the risk of pluvial flooding. The purpose of this study is to evaluate stormwater related flood risk in Hammarö Municipality. This is achieved using a Geographical Information system (GIS)based multicriteria analysis (MCA) approach, where stormwater flow paths, flood prone risk areas and potential pollutant loads are assessed. The study also identifies suitable stormwater management measures for areas classified as high risk. The results indicate that watershed delineation and stormwater flow patterns are strongly influenced by rainfall quantity and topography, which further also affect the dispersion across the land surface. Low-lying areas and depressions are particularly prone to flooding and several buildings within the study area are identified as at high risk. Pollution loads are highly connected to land use and landcover, where urban areas include higher concentrations compared to natural landscapes. Nature based solution (NBS) are identified as the most suitable mitigation measures, as the approach can reduce the flood risk by retention properties but also lowering pollutant loads through infiltration. Implementation of sustainable stormwater management, particularly focusing at already built environments, could enhance resilience to flooding, reduce environmental impact while simultaneously providing other important climate adaptation functions for Hammarö Municipality.