Att förebygga översvämningar med hjälp av konceptet Sponge city : En fallstudie av Hemlingby i Gävle

Sammanfattning: Climate change is predicted to cause an increase in cloudbursts and heavy precipitation, which makes urban flooding an issue that needs to be dealt with. The term Sponge city is a theory that intends to deal with urban flooding and worsening water quality in urban areas with absorption. The study area Hemlingby is an area that has been prone to flooding before, for instance on the 17–18 of August 2021. The area is located about 3 km from the city center Gävle with Hemlingbybäcken running north through the study area. The study was performed in several parts, the first was to use the GIS tool ArcMap 10.8 and hydraulic software CAESAR-lisflood 1.8 to investigate which areas are considered sensitive. In ArcMap 10.8, a bluespot map was created to estimate how much water is needed to fill different areas of Hemlingby, and in CAESAR-lisflood 1.8, the flood inundation area was mapped based on different water flow scenarios. Subsequently, two site visits were made to the study area to photograph and validate the results from the GIS analyses. Based on the GIS analyses, an interview with the municipality of Gävle and an extensive literature analysis, measures were identified that suited both the concept and the study area. The results show what affects the drainage in Hemlingby and how it could be improved through the use of Sponge city. Hemlingbybäcken, which is easily flooded by large water flows, and the topography of the area are factors that have been identified as particularly problematic for the study area's drainage. To show how the area could be planned after the Sponge city concept, proposals for both types of measure and location have been presented, also restrictions and how similar concepts can be applied in other areas are presented. Given that the frequency and intensity of future cloud bursts are not known, there is no answer as to whether the measures presented in the study would stop the study area from being flooded in the future. Especially when data and statistics from previous rainfall were missing, the area's exact reaction to a cloud burst could not be analyzed. On the other hand, it is possible to determine from the analyzes in the method that the study area was not adapted to the type of downpour it was affected by. Therefore, measures aimed at Hemlingbybäcken become significant as the topography or soil type of the area is much more difficult to influence. In order to investigate exactly what impact the proposed measures would have on Hemlingby, further studies need to be carried out to map both the collection capacity and the impact on Hemlingbybäcken the proposal has.