Vulnerability assessment of urban flooding in Lerum - Municipality and study of effectiveness of blue-green mitigation measures using software MIKE 21 and SCALGO Live

Examensarbete för masterexamen
Adhikari, Utsav
A much-realized consequence of climate change is shift in precipitation pattern and increase in extreme rainfall events. Moreover, growing urbanization trend associated with population and wealth growth has caused increase in impervious surfaces, while lowering groundwater recharge. In Sweden, the annual precipitation amount is predicted to increase consistently towards the end of this century thus increasing the likelihood of urban flooding risk. Lerum Municipality has realized this consequence of climate change and prepared a flood map for the municipality using a 2D hydrodynamic model to study the urban flooding risks and develop strategies to reduce these risks. In the thesis work, this flood map was utilized to investigate infrastructure vulnerable to flood and to locate areas where risks to human life can arise. Further, this thesis work has also supported the municipality to develop and investigate climate change adaptation strategies to reduce or eliminate urban flooding risk for two study areas – Hulan and Berghultskolan. Using GIS analysis, high flooding risk was obtained for both study areas affecting mostly residential houses and residential streets. Appropriate blue-green measures were proposed to regulate the stormwater runoff in both upstream and downstream areas. The effectiveness of the proposed measures was tested using two computer models - SCALGO Live and MIKE 21, and the results were compared. Similar results were obtained from both models, showing that blue-green measures are very effective in regulating stormwater runoff. Even though flood volume was significantly controlled in the Hulan area, there was still risk of flooding at the downstream point. However, the blue-green solutions proposed in the Berghutskolan area were successful in protecting the area from flooding risk. Sensitivity tests were performed for the proposed solution i) by testing against a more extreme rainfall event and ii) by changing the size of the solution by 10 percent. Uncertainties associated with model calibration, analysis technique and limitations of software were studied. Finally, recommendations for future studies as well as alternative flood mitigation solutions were suggested to the municipality based on the data obtained from the results and their critical analysis performed during the study.
blue-green solutions, urban flooding, hydraulic modelling, climate change
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