University of Twente Student Theses
Preparing polders for extreme weather events : Strategies to reduce flooding
Nannes, L.M.C. (2023) Preparing polders for extreme weather events : Strategies to reduce flooding.
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| Abstract: | The goal of this thesis is to investigate how flooding in polders during the preparation phase of an extreme weather event can be reduced, taking climate change into account. This research emerges from the identified gap in literature, where it is indicated how flooding can be reduced by implementing structural measures, but limited to no research has been done into measures that can be employed in the preparation phase of an extreme weather event. Moreover, research has been done on how to protect polders from fluvial flooding, but less research is done into which measures can be taken to protect for flooding caused by extreme precipitation events. In this research, the Zijpepolder is used as a case study to test how flooding can be reduced in polders during the preparation phase of an extreme weather event. The Zijpepolder has experienced flooding due to an extreme precipitation event in June 2021. To accomplish the aim of this research, it was first investigated what possible measures could be taken in polders during the preparation phase of an extreme weather event to reduce flooding. Secondly, the measures were tested and assessed using a multi criteria analysis. Then, a sensitivity analysis was performed, in which the area-specific terrain characteristics were varied. This sensitivity analysis was used to generalise the results of the Zijpepolder to an advice on how to reduce flooding in polders in general. To investigate which measures could potentially reduce flooding, expert interviews were conducted and literature research was done. By applying these methods, four measures appeared to possibly reduce flooding in polders. These measures were; creating a water level buffer, activating the old mills in the area, installing temporary flood barriers, and installing emergency pumps. To investigate which of these measures is most effective in reducing flooding, the measures were assessed on their performance using a multi criteria decision analysis. Flood duration, maximum water level, flood damage, and inundated area were used as criteria. To test the measures for these criteria, the 3Di hydrodynamic flood modelling program was used. Climate change was taken into account by choosing to test the measures for precipitation scenarios of 2050. From this multi criteria decision analysis, the water level buffer measure appeared to be most effective with a score of 1.86. The emergency pumps measure, the activating old mills measure, and the temporary flood barriers measure, scored 1.08, 0.74, 0.32 respectively. The major difference in the performance of the water level buffer measure and the emergency pumps measure could be found in the maximum water level criteria. The water level buffer measure scores 0.80 here and the emergency pumps measure scores 0.18. To check for uncertainties in the model results, a sensitivity analysis for the water level buffer measure was performed. For this sensitivity analysis the infiltration rate, the storage capacity, the friction, and the interception capacity were varied over a range from -30% to +30%. It appeared that especially the flood duration and the maximum water level were highly sensitive for a decrease in infiltration rate. A decrease in infiltration rate of 30% led to an increase of 103.3% and 24.3% for flood duration and maximum water level respectively. A flow chart and the sensitivity analysis were used to form an advise for the Zijpepolder on the reduction of flooding. Subsequently, a broader recommendation was given for polders in general. There can be concluded that, to reduce flooding of polders during the preparation phase preceding an extreme weather event, taking climate change into account, the water level buffer measure is on average most effective. More specifically, the water level buffer appeared to be most effective in reducing the flood duration and the maximum water level in polders. Activating the old mills appeared to be most effective in reducing flood damage, and the emergency pumps measure appeared to be most effective in reducing the inundated area. For areas with a reduced infiltration rate, or a reduced storage capacity compared to the Zijpepolder, the water level buffer measure is significantly less effective. With this conclusion, the research objective has been achieved. Due to the limited timeframe of this study, decisions were made that could potentially affect the results of the research. To determine the flood duration and maximum water level, five locations within the polder were chosen to be tested. These locations directly influence the results of the flood duration and the maximum water level. When different test locations were used, it might be possible that the results would have been different. That is why it is recommended for future research to test more locations within the polder to check if the water level buffer measure then still appears to be most effective. There is also recommended to do further research into the effects of the water level buffer measure on its surroundings. There are risks associated with draining the polder during summer. If the precipitation then falls in the adjacent polder, the whole polder will be dry. Future research should critically weigh the risks of this measure against the benefits. In this way, it can be decided if and how this measure can be put into practice safely. |
| Item Type: | Essay (Bachelor) |
| Faculty: | ET: Engineering Technology |
| Programme: | Civil Engineering BSc (56952) |
| Link to this item: | https://purl.utwente.nl/essays/95829 |
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