Jaap van Thiel de Vries

A New Alternative to Saving Our Beaches from Sea-Level Rise: The Sand Engine

ABSTRACT Stive, M.J.F.; de Schipper, M.A.; Luijendijk, A.P.; Aarninkhof, S.G.J.; van Gelder-Maas, C.; van Thiel de Vries, J.S.M.; de Vries, S.; Henriquez, M.; Marx, S., and Ranasinghe, R., 2013. A new alternative to saving our beaches from local sea-level rise: the sand engine. A boldly innovative soft engineering intervention, comprising an unprecedented 21.5 Mm3 sand nourishment known as the Sand Engine, has recently been implemented in the Netherlands. The Sand Engine nourishment is a pilot project to test the efficacy of local mega-nourishments as a counter measure for the anticipated enhanced coastal recession in the 21st century. The proposed concept, a single mega-nourishment, is expected to be more efficient, economical, and environmentally friendly in the long term than traditional beach and shoreface nourishments presently being used to negate coastal recession. Preliminary numerical model results indicate that this local nourishment will result in the widening of the beach along a 10 to 20 km stretch of the coastline and a beach area gain of 200 ha over a 20-year period. First observations show indeed a redistribution of the sand feeding the adjacent coasts, roughly 40% toward the south and 60% toward the north. While the jury is still out on this globally unique intervention, if proven successful, it may well become a global generic solution for combating sea-level-rise driven coastal recession on open coasts.

Title: MICORE: DUNE EROSION AND OVERWASH MODEL VALIDATION WITH DATA FROM NINE EUROPEAN FIELD SITES

In this paper we present the first results of beach profile hindcasting with XBeach using recently measured coastal data acquired under storm conditions at eight European sites, including a comparison to model results obtained with off-the- shelf models. The results show consistently that the XBeach has skill in predicting the coastal profile, albeit that in most cases the erosion around the mean water line is overpredicted and the depositions at the lower beach face are overpredicted. The causes for this model effect are under active investigation but not resolved yet. Likely candidates are the modeling of onshore (asymmetry) transports which reduces the offshore transports due to undertow (currents) or the modeling of sediment motion in the swash zone.

Coastal Mangrove Squeeze in the Mekong Delta

ABSTRACT Phan, L.K.; van Thiel de Vries, J.S.M., and Stive, M.J.F., 2015. Coastal mangrove squeeze in the Mekong Delta. The role of mangrove forests in providing coastal zone stability and protection against flooding is increasingly recognized. The specific root, stem, and canopy system of mangroves is highly efficient in attenuating waves and currents. The sheltered environment created by a healthy mangrove forest offers great sedimentation potential in case a sediment source is available. However, the once-abundant mangrove forests in the Mekong coastal delta are becoming rapidly depleted. Especially along the Mekong eastern and southeastern coast, mangrove degradation and rapid coastline erosion are observed at many locations. At these locations, the mangrove forests usually consist of a narrow strip only, sometimes as narrow as 100 m. This mangrove squeeze is mainly due to the construction of sea dikes in a quest for the creation of space for cultivation and the prevention of salinity intrusion. The basic assumption behind our work is that there is a critical minimum width of a coastal mangrove forest strip to keep its ability to stay stable or, once surpassing the minimum width, to promote sedimentation. The larger the width the more efficient the attenuation of waves and currents will be, offering both a successful seedling and sedimentary environment. Our analysis of available data both from literature and from satellite observations supports our basic assumption: an average critical width of 140 m is found for the southeastern and eastern Mekong Delta coast as a minimum width to sustain a healthy mangrove forest. To further our insights into the efficiency of mangrove to attenuate wave energy as a function of their width we have applied a state-of-the-art wave propagation model that includes both short and long waves. Our results confirm earlier results from the literature that short waves are indeed attenuated very rapidly over distances shorter than the critical width, but as we show for the first time infragravity waves penetrate over much larger distances. We therefore hypothesize that the decay of long waves plays a crucial role in the health of the mangrove.

Applicability of video-derived bathymetry estimates to nearshore current model predictions

ABSTRACT Radermacher, M., Wengrove, M.E., Van Thiel de Vries, J.S.M., Holman, R.A., 2014. Applicability of video-derived bathymetry estimates to nearshore current model predictions. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 290–295, ISSN 0749-0208. In the framework of swimmer safety, coastal managers desire accurate nearshore current predictions obtained from numerical models. To this end, detailed and up-to-date bathymetry is a necessity. Remote sensing techniques for bathymetry estimation are a promising solution. The focus of this paper is to assess the performance of wavenumber-based bathymetric inversion using Argus imagery (also known as the cBathy algorithm) as a feasible input bathymetry for numerical models to make reasonable nearshore current predictions. Numerical flow simulations on a cBathy bed are compared to simulations on an in-situ surveyed bathymetry. Results demonstrate that simulated nearshore currents on a cBathy bathymetry have a root-mean-square error in the order of 10 cm/s (magnitude) and 40 degrees (direction) when compared to simulated currents on a surveyed bathymetry. In the intertidal zone cBathy should be combined with a different method for bathymetry estimation in order to decrease these errors.

Intertidal beach classification in infrared images

ABSTRACT Hoonhout, B.M., Baart, F., Van Thiel de Vries, J.S.M. 2014. Intertidal Beach Classification in Infrared Images. In: Green, A.N. and Cooper, J.A.G. (eds.), Proceedings 13th International Coastal Symposium (Durban, South Africa), Journal of Coastal Research, Special Issue No. 70, pp. 657–662, ISSN 0749-0208. Digital imagery is a powerful data source for coastal monitoring, maintenance and research. It provides high-resolution measurements in both time and space. The size and resolution of long-term imagery datasets provide great opportunities, but also pose problems of tractability in the data analysis. In order to fully use the possibilities of these datasets, reliable and automated classification of images is essential. This paper discusses an automated classification approach based on Conditional Random Fields (CRF). The algorithm is applied in pixel space only. Therefore it does not rely on in-situ measurements, nor is there a need for image rectification. The algorithm consists of three steps: segmentation, feature extraction and model training and prediction. We applied the method to a coastal thermal infrared image stream that monitors the wetting and drying of the upper intertidal beach in relation to tide and meteorological parameters. Classification of the upper intertidal beach provides information on the potential sources of Aeolian sediment. The use of 62 extracted features and structured learning proves to provide significantly better classification results compared to algorithms solely based on intrinsic intensity features.