University of Twente Student Theses


Extrapolation of morphodynamics for the estimation of future seabed changes in the Europlatform area

Vinni, T. (2019) Extrapolation of morphodynamics for the estimation of future seabed changes in the Europlatform area.

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Abstract:Background Sand waves typically occur in sandy shallow seas such as the North Sea and they are induced by tidal currents. Sand waves are dynamically active features with migration rates up to a few meters per year posing a serious threat to the safety of submarine structures. Thus, a detailed study of the sand wave characteristics (shape and migration rates) could be used in the strategy formulation process of offshore wind farms. Objectives This study aims to calculate the main characteristics (height, length, asymmetry, migration and growth rate) of a sand wave field located in the vicinity of the Europlatform (North Sea). Furthermore, it aims to identify correlation patterns between the migration rate and the sand wave shape. The measurements of 13 surveys (from 2006 to 2018) carried out at the study area have been used in the bathymetric analysis. The second objective of the study is to create a statistical predictive model that can be used to estimate future seabed levels. The predictive model has been developed, using the findings of the bathymetric analysis. Methods We use the Fourier analysis to filter bedforms, with shorter and longer wavelengths, from the sand wave signal. From the filtered seabed profiles, we determine the positions of crests and troughs and we calculate the sand wave characteristics using the method suggested by Knaapen (2005). The least square method has been used to define the best fitted regression model. The selected regression model has been extrapolated and we use the prediction bounds to define future minimum and maximum vertical positions of sand wave crests and troughs. Results From the bathymetric analysis, we found that the characteristics of the sand wave field show little, if any, variation over the study period (13 years). Furthermore, the predominant direction of the migration of the sand wave field is North East, which coincides with the steeper slope. The field comprises individual sand waves with average lengths and heights ranging from 117 to 347m and from 1.9 to 8.4m respectively. The mean (per individual sand wave) migration rates vary between 0.3 and 1.86m/yr to the North East. Lastly, it has been observed that a few sand waves migrate in the opposite direction of the steeper slopes. A statistically weak negative correlation has been revealed between migration rate and sand wave height and length. This study found no correlation between migration rate and sand wave asymmetry. Based on the predictive model and the suggested uncertainty bounds, the future seabed level changes have been estimated. Specifically, we found that the maximum potential rise and lowering of the seabed level in 2030 is 0.9m and -0.4m, respectively. The predicted seabed rising and lowering have been estimated with respect to the most recent bathymetrical survey (2018). Conclusion The proposed model could be used to improve the decision-making process by predicting minimum and maximum seabed level changes. However, the prediction model is not valid outside of the study area.
Item Type:Essay (Master)
Faculty:ET: Engineering Technology
Subject:56 civil engineering
Programme:Civil Engineering and Management MSc (60026)
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