Arjen Luijendijk

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.

The Lagos coast - Investigation of the long-term morphological impact of the Eko Atlantic City project

The Lagos coast has been suffering high rates of erosion since the construction of three harbour moles, i.e. the West Mole, East Mole and the Training Mole, at the tidal inlet connecting the Lagos Lagoon to the South Atlantic Ocean. To provide for a permanent erosion mitigation measure and to create residential and commercial area for circa 400,000 people, the Eko Atlantic City project has been initiated in 2008. In front of the eroded coast, approximately 9 km² of land will be reclaimed and protected by a revetment. In this study the long-term and large-scale morphological behavior of the Lagos coast is investigated and subsequently the long-term morphological impact of the project is assessed. First, a conceptual model is created, in which the historical development of the coast is discussed. The long-term morphological behavior of the coast downstream of the inlet is determined by two main factors: sediment accumulation at the West Mole and sediment import into the tidal inlet and the lagoon, induced by disturbance of the morphological equilibrium by sea level rise and dredging activities. Using the numerical simulation model Unibest, the long-term impact of Eko Atlantic City is assessed. It is concluded that the construction of Eko Atlantic City will not change the total erosion volumes downstream of the inlet. However, as the revetment of the project retains the coast, the erosion will be shifted towards downstream. Downdrift of the project, the erosion rates are locally relatively high. The shape of the sea defence has been designed to minimize the local erosion effect. A monitoring and mitigation strategy has been recommended to monitor this effect and instruct coastal protection management actions to be implemented if required.

The State of the World’s Beaches

Coastal zones constitute one of the most heavily populated and developed land zones in the world. Despite the utility and economic benefits that coasts provide, there is no reliable global-scale assessment of historical shoreline change trends. Here, via the use of freely available optical satellite images captured since 1984, in conjunction with sophisticated image interrogation and analysis methods, we present a global-scale assessment of the occurrence of sandy beaches and rates of shoreline change therein. Applying pixel-based supervised classification, we found that 31% of the world’s ice-free shoreline are sandy. The application of an automated shoreline detection method to the sandy shorelines thus identified resulted in a global dataset of shoreline change rates for the 33 year period 1984–2016. Analysis of the satellite derived shoreline data indicates that 24% of the world’s sandy beaches are eroding at rates exceeding 0.5 m/yr, while 28% are accreting and 48% are stable. The majority of the sandy shorelines in marine protected areas are eroding, raising cause for serious concern.

Shallow water bathymetry mapping using Support Vector Machine (SVM) technique and multispectral imagery

ABSTRACT Satellite imagery along with image processing techniques prove to be efficient tools for bathymetry retrieval as they provide time and cost-effective alternatives to traditional methods of water depth estimation. In this article, a nonlinear machine learning technique of Support Vector Machine (SVM) is used to derive shallow water bathymetry data along Sint Maarten Island and Ameland Inlet, The Netherlands, by combining echo-sounding measurements and the reflectance of blue, green, or red bands of Landsat Enhanced Thematic Mapper Plus (Landsat 7 ETM+) and Landsat 8 Operational Land Imager (OLI) imagery with 30 m spatial resolution. In the analysis, 80% of data points of the echo-sounding measurements are used for training and the remaining 20% data points are used for testing. The model utilizes the radial basis kernel function (nonlinear) and the other training factors such as the smoothing parameter, penalty parameter C, and insensitivity zone ε are selected and tuned based on the learning (i.e. training) process. The overall errors during test phases for Sint Maarten Island (1–15 m) and Ameland Inlet (1.00–3.50 m) are 8.26% and 14.43%, respectively, reflecting that the model produces significant estimations for the shallow depths ranges, considered in this study. The results obtained are also compared statistically with those estimated from the widely used linear transform model and ratio transform model, which establish a linear relationship between the water depth and band reflectances. Based on the results, it is evident that SVM provides a comparable or better performance for shallow depth ranges and can be used effectively for deriving accurate and updated medium resolution bathymetric maps.

COASTAL RESPONSE ON MULTIPLE SCALES: A PILOT STUDY ON THE IJMUIDEN PORT

Responses due to coastal interventions may occur at multiple temporal and spatial scales. The morphological development in such cases may be a result of an interactive behaviour between the different scales. To illustrate such behaviour, the IJmuiden port was selected as a pilot case. The IJmuiden case showed that computing the morphological developments around such local coastal interventions is not trivial. The dominant force in the considered case is a coupled behavior covering multiple scales, which does not allow for a simple sub-division of scales. So, one single numerical model is not able to resolve all relevant scales. Hence, a hybrid (multi-scale) modeling approach is required, in which two or more models are combined. The results presented in this paper show that a coupling between a coastline model and area model (bypass, currents) already improves the predicted coastline development and longshore sediment transport. Further strategic research is currently being undertaken to further investigate the sensitivities of a hybrid modeling approach with the ultimate goal to develop an integrated modeling system that is able to assess the impact of anthropogenic activities on all relevant spatial and temporal scales.

A QUALITATIVE ASSESSMENT OF CLIMATE CHANGE IMPACTS ON THE STABILITY OF SMALL TIDAL INLETS VIA SCHEMATISED NUMERICAL MODELLING

Tidal inlets are of great societal importance and are also the most morphologically dynamic regions in the coastal zone. Therefore, they are of great scientific interest. Their behaviour is governed by the delicate balance of oceanic processes such as tides, waves and mean sea level (MSL), and fluvial/estuarine processes such as riverflow. All of these processes can be significantly affected by climate change (CC) processes, which may result in negative physical impacts such as inlet closure/relocation, creation of new inlets, erosion of the coast adjacent to the inlet etc. Although CC impacts on some large tidal inlets (e.g. Wadden Sea inlets) have received some attention recently, the potential CC impacts on small tidal inlets (STIs) remain virtually unknown to date. Furthermore, whether currently available predictive tools are capable of simulating CC impacts on these systems also remains unknown. These knowledge gaps are a serious threat to effective adaptation to CC in STI environments. Just, this study attempts to investigate the potential range of CC impacts on the stability (i.e. closed/open state and locational stability) of STIs via the application of a sophisticated process based morphodynamic model (Delft3D) to strategically selected schematised inlet morphologies and forcing conditions. Results indicate that CC driven variations in system forcing are likely have profound impacts on inlet stability and also show that a process based coastal morphodynamic model (eg. Delft3D) is suitable for investigating potential CC impacts at small tidal inlets.

Climate Change Impacts on the Stability of Small Tidal Inlets: A numerical modelling study using the Realistic Analogue approach

Tidal inlets are of great societal importance as they are often associated with ports and harbours, industry, tourism, recreation and prime waterfront real estate. Their behaviour is governed by the delicate balance of oceanic processes (tides, waves and mean sea level), and fluvial/estuarine processes (riverflow and heat fluxes), all of which can be significantly affected by climate change (CC) processes. This study investigates the potential range of CC impacts on the stability (closed/open state and locational stability) via the application of a sophisticated process based morphodynamic model (Delft3D) to strategically selected schematized inlet morphologies and forcing conditions. Results show that, under worst case scenario conditions, the integrated effect of climate change driven increase in mean sea level, wave height and wave angle may significantly change inlet stability condition.

Author Correction: The State of the World’s Beaches

A correction to this article has been published and is linked from the HTML and PDF versions of this paper. The error has not been fixed in the paper.