A process-based modelling study on the morphological response of the Bacton Sandscaping project
J.P.D. van der Veen (TU Delft - Civil Engineering & Geosciences)
Matthieu de Schipper – Mentor (TU Delft - Coastal Engineering)
SGJ Aarninkhof – Graduation committee member (TU Delft - Hydraulic Engineering)
AP Luijendijk – Graduation committee member (TU Delft - Coastal Engineering)
BC Van Prooijen – Graduation committee member (TU Delft - Environmental Fluid Mechanics)
C.M. van der Boon – Graduation committee member (Royal HaskoningDHV)
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Abstract
The last couple of years, the interest in large nourishments, that also feed the adjacent coast, has increased. A feeder nourishment is suggested to be cost effective as well as ecological more beneficial than traditional nourishments. However, their behaviour is more complex and the need for better morphological predictions has increased. Earlier research has given insight in the morphological behaviour and the driving forces of a feeder nourishment in the Netherlands (the Sand Engine). A new feeder nourishment was constructed in October 2019 at the coast of Bacton (UK). This provides a new opportunity to evaluate the feeder nourishment behaviour outside the Netherlands. This thesis describes the results of a numerical morphological model of this feeder nourishment called Bacton Sandscaping (hereafter: BSS) A full bathymetric survey was conducted three times with echo-sounder, LiDAR scanner and photogrammetry during the first half year of the BSS. The surveys showed that the erosion of the first two months is four times higher than the erosion volumes of the months following, indicating a strong initial response. Moreover, a clear link between the morphological response of the sub-aerial beach and submerged beach was found. The numerical model has been calibrated and validated extensively with the bathymetric data of the first half year of this nourishment. The model is very well capable of representing beach volume changes and scores excellent on the Brier skill score. To obtain this excellent score, similar calibration parameters for waves were used as in the Sand Engine case in the Netherlands. The strength of this model was then used to evaluate the effect of offshore wave heights on the erosion volumes of the nourishment and showed that significant wave heights lower than 1 meter are causing 57% of the observed erosion. As the model is well capable of simulating the first half year it is then assumed that the model is also capable of simulating beach volume changes for a different grain size as well as different wave event intensities. The model predicted that sediment grain size and wave event intensities do not have a significant effect on the morphological behaviour of the BSS, therefore the initial state of the nourishment is more important in how the nourishment will evolve. The BSS model is a step forward in the understanding of the morphological behaviour of feeder nourishments and can be used for future modelling purposes of the BSS.
For future feeder nourishments it is advised to focus more on the design shape of the nourishment and not so much on the wave event intensity and grain size of the nourishment. In addition, future calibration of feeder nourishments can further point out if feeder nourishments can use similar calibration parameters for waves.