coastal development

Sint Eustatius is a Caribbean island located in the north of the Lesser Antilles. The coastline west of the capital, Oranjestad Bay, is of vital importance to the island as it is here where tourism, recreation, the harbour and historical ruins are located. On the other hand, Oranjestad Bay has a heavily fluctuating beach, which is undesirable. The Public Entity of St. Eustatius is investigating the possibility of a coastal solution that could preserve and extend this beach. However, there is insufficient knowledge of the hydrodynamic processes and morphology available to design a solution. By analysing the morphological system, this study aims to advise the Public Entity of St. Eustatius on the decision for a coastal solution to create a beach in Oranjestad Bay.

A literature study was performed to obtain basic knowledge of the coastal system of Oranjestad Bay. A two-dimensional numerical Delft3D model was then developed to gain more in-depth knowledge of the wave, current and sediment patterns. The result of both findings is combined in a conceptual model, where the cause of the beach fluctuations along Oranjestad Bay was analysed. Based on the system knowledge and stakeholders’ demands and regulations, three alternatives to create a beach at Oranjestad Bay are proposed. The alternatives are qualitatively verified and evaluated with a multi-criteria analysis and cost-value ratio.

The literature review shows that Oranjestad Bay has the characteristics of a wave-dominated coast. The seasonal wave climate has a strong influence on the beach fluctuations that occur in Oranjestad Bay. The influence of tides and wind on sediment dynamics is expected to be minimal. The modelling study concluded that the wave climate can be described by three main wave conditions, namely a sea condition, a storm condition and a swell condition. The different hydrodynamic and morphodynamic characteristics of these conditions provide a reasonable simulation of the coastal processes in Oranjestad Bay. The model results give an impression of the seasonal wave climate and a net northward sediment transport capacity is found. These results are consistent with the expected coastal morphodynamics found in the literature study. The effect of a storm is less well represented in the modelling study. This limitation is caused by the modelling approach. In addition, there are some uncertainties in the model due to the lack of detailed coastal data in the nearshore. The conceptual model indicates that the coast of Oranjestad Bay may experience seasonal gradients
in alongshore sediment transport leading to beach fluctuations. From April to September, beaches are likely to erode due to net northward sediment transport. In addition, beaches erode due to periodic storm conditions that occur from June to November. It has been found that the recovery of beaches after a storm varies along Oranjestad Bay. Scubaqua beach recovers much faster than the beach at Smoke Alley. This is due to the larger sediment transport capacity in the alongshore direction at Smoke Alley beach, the amount of larger cobbles on the shoreline of Smoke Alley and the lack of sediment north of Smoke Alley...

Part of the larger The impacts of climate change on Bonaire (2022-present) report available here.
 

Summary

Coastal hazards pose a significant threat to small islands, especially in combination with Sea Level Rise (SLR). Currently, the small Caribbean island of Bonaire is poorly protected against coastal flooding and there is a lack of local knowledge on potential adaptation options and their benefits and trade-offs. This study aims to fill this gap by evaluating how different coastal adaptation options to protect Bonaire are valued, considering economic, social, environmental, and technical criteria. This is evaluated using a participatory Multi-Criteria Analysis (MCA) that includes key stakeholders through semistructured interviews and the use of an online questionnaire. A wide variety of coastal adaptation options, ranging from grey infrastructure to softer Nature-based Solutions (NbS), is assessed based on an interdisciplinary set of 10 different criteria, providing a holistic view of the consequences of each option. The results show that NbS, especially mangrove restoration, and spatial zoning measures are overall perceived to be most beneficial. The least favourable adaptation strategies include the construction of any type of seawall and doing nothing. While an MCA does not lead to a final perfect solution, it does provide valuable comparative information about potential future adaptation strategies for Bonaire, which can be used to aid policy makers in the decision-making process. Moving forward, it is important to further strengthen the results of this study by conducting additional quantified analyses, including an evaluation of the spatial suitability of specific measures or combinations of measures. Moreover, to ensure public support for any final policy decisions, regardless of the specific measures that a

Part of the larger The impacts of climate change on Bonaire (2022-present) report available here.
 

Summary

This study aims to identify the extent to which Bonaire’s buildings and critical infrastructure will be directly impacted by future climate change, focusing on floods and storms. To do so, we combine open-source information on exposure and vulnerability with locally acquired detailed information through interviews and fieldwork. We introduce a new method, called neighbourhood sampling, to produce accurate local data on building values to overcome data scarcity. The results show that in 2050 a 1/100 flood event may affect at least 54 buildings, depending on the climate scenario, most of which are residential along the southern coastline, leading to a maximum of 14.4 USDm in damages. In 2050, no critical infrastructure other than roads will be hit by a flood. Using our approach, we find no damages due to storm hazards, which can be attributed to the limited availability of knowledge on wind vulnerability for Bonaire. The results are assumed to be underestimated due to inaccuracy in the applied hazard intensity maps, which can significantly impact the estimated flooding damages and associated costs. This research is anticipated to serve as a foundation for more sophisticated local climate hazard research on scarce data locations, and Bonaire specifically. Moreover, it provides a starting point for further research on adaptation measures on Bonaire, as it shows which areas are most vulnerable to flooding.