University of Twente Student Theses
Storage improvement of urban water catchments in Ede using the SOBEK model
Hanning, J. (2023) Storage improvement of urban water catchments in Ede using the SOBEK model.
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| Abstract: | In the context of climate change and ongoing development in flood-prone areas, Europe faces the potential for an unprecedented increase in flood risk. The Netherlands, with its low-lying geography and high population density, is particularly vulnerable to this threat (Koopman, Kuik, Tol, & Brouwer, 2015). Implementing storage mechanisms to reduce regional flood peaks has been identified as a cost-effective adaptation strategy (Dottori, Mentaschi, Bianchi, Alfieri, & Feyen, 2023). The Waterboard ’Vallei en Veluwe’, responsible for managing the urban surface water system, has identified that the peak discharges in neighborhoods constructed in the 1970s and 1980s exceed the design norm of 3 l/s/ha. Although storage facilities are available, their utilization remains suboptimal. The objective of this thesis was to investigate the causes of underutilization and propose potential solutions for improving storage capacity in these urban catchments. The research focused on a case study of two catchments in Ede, Gelderland. To begin, an enhanced SOBEK model was constructed by building upon an existing model. Data from the waterboard, municipality, and national authorities were integrated into the model. Remarkable deviations between the new and old data were observed. Measured discharge data from automatic weirs were used to calibrate the groundwater model. The model is verified through a site visit and validated using measured data. The performance of each model update is evaluated against the measured data using the Nash-Sutcliffe efficiency (NSE). Significant improvements in model performance (NSE increasing from -1.8 to 0.4) are observed, with the most substantial enhancement resulting from updating the paved area and overflow locations within the model. Subsequently, the constructed model is utilized to identify the causes of underutilization. Hypotheses are tested by simulating peak events and assessing water levels. The simulations reveal that water levels can increase by up to 2 meters before flooding occurs. Additionally, the steady water levels exhibit minimal changes, supporting the hypothesis that the storage facilities are consistently full. Consequently, a full storage system leads to the direct discharge of peak events. It is concluded that the water systems were not originally designed to store peak discharges but rather to drain groundwater from surrounding neighborhoods. Implementing additional drainage methods can reduce the need for lower water levels, thus allowing for increased utilization of storage capacity. To pinpoint the specific problem areas, a map illustrating the relative discharge in l/s/ha per weir is produced. This map exposes the bottlenecks in the water system and can be used to identify the starting point for implementing interventions. The relative discharges downstream of both catchments exceed the norms, with values of 7.6 and 7.4 l/s/ha. Finally, the potential solutions are modeled to assess their impact on peak discharge. Considering budgetary, temporal, and technical constraints, the selected intervention is the improvement of weirs, specifically by incorporating V-notch structures. V-notch weirs are chosen for their ability to modify discharge capacity based on water heights. Implementing V-notch weirs with heights of 0.3 and 0.5 meters results in a reduction of peak discharge by 20% and 40% respectively. The water levels upstream of the weirs temporarily rise but are lowered within 48 hours to limit changes in groundwater levels. Incremental implementation of V-notch weirs enables data collection between interventions, which facilitates the validation of changes in discharge, surface water levels, and groundwater levels. To implement the proposed interventions across the entire management area of the Waterboard, improvements in urban water models are necessary. Undertaking a comprehensive update of the urban model for the entire management area in a single project is more cost-effective, as the process of improving the model is time-consuming and independent of the amount of data. However, achieving this requires enhancing the integration of data between municipalities and the waterboard. Benefit linkage can be utilized to foster comprehensive and long-term collaboration. The most important municipal data for urban models are overflow locations and sewage capacity. The collaboration requires clear storage definitions, peak storage should be redefined and based on the amount of water that is not directly discharged, rather than the absolute volume of the storage facility. |
| Item Type: | Essay (Bachelor) |
| Faculty: | ET: Engineering Technology |
| Programme: | Civil Engineering BSc (56952) |
| Link to this item: | https://purl.utwente.nl/essays/95257 |
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