University of Twente Student Theses
Calibrating a hydraulic river model using bathymetry and roughness: A case study on the River Waal
Gerrits, G.J. (2023) Calibrating a hydraulic river model using bathymetry and roughness: A case study on the River Waal.
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| Abstract: | Rivers play an important role in shaping the earth's landscape and serve as a crucial resource for various human activities. However, rivers can also be the cause of flooding, which can be very dangerous for humans and other species living near the rivers. It is therefore important to accurately predict the behaviour of a river. This can be achieved by using hydraulic river models, which are valuable tools used to simulate and predict flow patterns, water levels, and sediment transport in river systems. To make the predictions of these models as accurate as possible they are calibrated by adjusting one or more model parameters. The roughness of the river bed is commonly used as a calibration parameter for hydraulic river models because it is one of the main sources of uncertainty. An alternative to the roughness that is not used as often as a calibration parameter is bathymetry. The roughness and the bathymetry have the largest impact on predicting inundation and flow characteristics. However, the number of studies that include bathymetry in the calibration process is limited. It would therefore be interesting to investigate the use of bathymetry as a calibration parameter in a hydraulic river model. The bathymetry can then be compared to the roughness based on the effect it has on the water level, and the accuracy of the calibration when used as a calibration parameter. The objective of this master thesis is to determine and compare the effect of the roughness and the bathymetry as calibration parameters on the accuracy of simulated water levels in a hydraulic river model. The study area that is used is the river Waal from the observation station Pannerdense kop to the observation station Hardinxveld. To accomplish the objective a sensitivity analysis has been performed to compare the effect of the roughness and the bathymetry on the water level. Thereafter both parameters are used as calibration parameters to simulate the water level for the discharge wave of 1995. The calibrated models are subsequently validated using the 1993 and 2011 discharge waves. The accuracy in the calibration and validation is determined using the Root Mean Square Error (RMSE). This is all done using the modelling software SOBEK. The most important result of the sensitivity analysis was that the roughness had a larger effect on the water level than the bathymetry for the chosen roughness value range and bathymetry height range. The bathymetry showed a linear and the roughness a slightly nonlinear relationship to the water level. The calibration resulted mainly in increases in the roughness values and the bathymetry height. The validation yielded comparable average RMSE values for the roughness and the bathymetry. The bathymetry showed slightly higher RMSE values on average, but these differences were not significant enough to deem the bathymetry less accurate as a calibration parameter than the roughness. Overall, the results of this research show that the influence of the roughness on the water level is larger than the bathymetry. However, the accuracy of the roughness and bathymetry is comparable when using them as calibration parameters for a hydraulic river model. It is recommended to do further research into the effect of bathymetry as a calibration parameter on both the water level and the accuracy of the calibration. This can be performed for a different study area, using a different modelling approach, or for lower discharges. It is also recommended to do further research into the influence that the shape of a cross-section has on the effect of the bathymetry on the water level. |
| Item Type: | Essay (Master) |
| Faculty: | ET: Engineering Technology |
| Subject: | 56 civil engineering |
| Programme: | Civil Engineering and Management MSc (60026) |
| Link to this item: | https://purl.utwente.nl/essays/95264 |
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