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Flash flood modeling for geul catchment, considering different mitigation measures for july 2021 extrem rainfalls.

Mohammed, M. Jeneto (2022) Flash flood modeling for geul catchment, considering different mitigation measures for july 2021 extrem rainfalls.

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Abstract:In July 2021, Belgium, Germany, and the Netherlands experienced major floods as a result of heavy rainfall with 1/500–1/1000 return periods. On the Geul watersheds, specifically in Valkenburg city, the flood has caused economic damage estimated at around 400 million euros. Therefore, because of the increased risk posed by flood hazards due to climate change, there was a need for effective disaster management that considers the future implications of current mitigation and adaptation strategies. Thus, this study has investigated how a July 2021 flash flood and future flood events can be reduced on downstream parts of the catchment by applying different mitigation measures. Flood simulation was made by using the physically-based LISEM Integrated Spatial Earth models (LISEM). Calibrated mode results showed an NSC and RMSE performance of 0.50 and 0.30, respectively. Subsequently, the study investigated four potential mitigation measures. Initially, the flood simulation was made with the scenario of improving farming practices by selectively increasing the hydraulic conductivity and porosity of the soil in agricultural fields. With both slightly and significantly enhanced agricultural practices, the simulation showed that the water level is identical to the calibrated simulation. Additionally, given Limburg's current farming techniques and its limited spatial coverage, further improving farming practices has little impact on the Geul flooding. Thus, based on the model results, the farming scenario was considered ineffective. Secondly, the simulation has made by increasing the volumes of the current water buffer. The 2m and 4m increment in the depth of the existing water buffer maximizes the current volumes from 1 million m3 to 3 million m3 and 6 million m3, respectively. The water buffer scenario initially slows down the water level while the peak remains the same. As a result, the effectiveness of water buffers was volume-dependent and required further reinforcement with non-structural measures. Thirdly, the flood simulation was made by increasing forest land by 5%, which improved the peak water level and velocity by 10% each. Moreover, the combination of the water buffer and afforestation scenario helps to slow down the water level by 3-4 hr and improve the peak of water level and velocity by 10%. Thus based on the model result, the combination of water buffer and afforestation scenario is considered adequate. Lastly, given the meandering nature of the Geul and its huge demand for the area and cost, the room for the river scenario was considered impractical. While these studies explain, the causes and potential solutions for flash floods in the Geul area and Valkenburg, more detailed work on the spatial flood simulation and cost-benefit analysis must be taken to improve the certainty of the results.
Item Type:Essay (Master)
Faculty:ITC: Faculty of Geo-information Science and Earth Observation
Programme:Geoinformation Science and Earth Observation MSc (75014)
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