With increasing sea level rise, increasing volumes of sand are required to nourish the Dutch coast. To satisfy this demand, increasing volumes of sediment are extracted from the Netherlands Continental Shelf (NCS). To ensure future availability of sediment, make efficient use of limited space on the NCS and reduce sailing costs, the policy has now changed to allow for deep sand extraction with a pit depth exceeding two meters. However, the impact these deep extraction pits have on their environment may be severe.
Firstly, literature suggests that the sea bed may not recover from the sand extraction and that the pit will remain permanently present, with some researchers even terming them “scars in the sea bed” (Witbaard & Craeymeersch, 2023).
Secondly, the extraction disturbs bedforms that may already be present. In this study, we specifically focus on sand waves: wave-shaped dynamic bed features with a wavelength in the order of hundreds of meters, a height of multiple meters and migration rate of meters per year. Due to the sand extraction, the sand waves may locally be removed or altered. In case of a flat bed prior to extraction, the extraction may induce sand wave formation. Conversely, if sand waves were present prior to extraction, these do not necessarily regenerate (Krabbendam et al., 2022).
Thirdly, sand extraction pits may function as a fine sediment sink due to the local reduction in flow velocity. Consequently, fine (and potentially cohesive) sediment settles in the pit, changing the sediment composition. This doesn’t only have a large impact on sea life and benthic organisms, but also on bedform formation: it is suggested that only 10% mud can already prevent sand wave formation (Baas et al., 2016).
Thus far, a linear sand wave model has been developed to investigate the interaction between sand wave formation and cohesive sediment presence (see Ploeg et al., 2024). In this assignment, we can use this model to systematically explore:
- The impact of different extraction strategies (width and depth of the pit, slopes of the pit) on sand wave formation and sediment sorting (see e.g. Roos et al., 2005).
- The impact of multiple non-cohesive (sandy) and a single cohesive (muddy) sediment fraction on sand wave formation and pit evolution.
It should be noted that there is still some freedom in shaping the assignment. Additionally, the model development for this assignment has already been done. No major model development or programming is to be expected, although application of the model will still require some programming and math. Programming for this assignment is in MatLab.
References
- Baas, J. H., Best, J. L., & Peakall, J. (2016). Predicting bedforms and primary current stratification in cohesive mixtures of mud and sand. Journal of the Geological Society, 173(1), 12–45. https://doi.org/10.1144/jgs2015-024
- Krabbendam, J. M., Roche, M., Van Lancker, V. R. M., Nnafie, A., Terseleer, N., Degrendele, K., & De Swart, H. E. (2022). Do tidal sand waves always regenerate after dredging? Marine Geology, 451, 1–8. https://doi.org/10.1016/j.margeo.2022.106866
- Ploeg, W., Roos, P.C., Borsje, B.W., Hulscher, S.J.M.H. (2024). Idealised modelling of the influence of cohesive sediment on sand wave dynamics. Abstract from 21st Physics of Estuaries and Coastal Seas Conference, Bordeaux, France. https://pecs2024.sciencesconf.org/data/pages/PECS_2024_ Book_of_abstracts.pdf
- Roos, P. C., Blondeaux, P., Hulscher, S. J. M. H., & Vittori, G. (2005). Linear evolution of sandwave packets. Journal of Geophysical Research: Earth Surface, 110(4), F04S14, 1-10. https://doi.org/10.1029/2004JF000196
- Witbaard, R., & Craeymeersch, J. (2023). Littekens op de zeebodem. Een onderzoek naar de faunistische effecten op lange termijn van diepe zandwinning voor de Nederlandse kust (Nos. 2023–01; pp. 1–42). Netherlands Institute for Sea Research (NIOZ). https://doi.org/10.25850/nioz/7b.b.8d
Supervision
Are you interested in this assignment? Contact the Master thesis coordinator.
