Dikes constructed of a sand core, clay cover and natural vegetation as (landside) slope protection are common flood defence structures in the Netherlands. The design parameters, such as the crest height of dikes, are determined through risk assessment to reduce the remaining probability of a failure mechanism, such as overflow. Little is known about the exact process leading to failure of the typical Dutch dikes in case the failure conditions actually occur. The most notable floods in the Netherlands have all been caused by dike breaching, where local damage in the dike lead to breach formation. This research describes the process of breach formation due to overflow and determines what design parameters affect the resistance of a dike against breaching. The proposed model (BRAM, a Breach Resistance Analysis Model) combines existing methods to determine the time-to-failure of the grass and clay cover with a newly developed process-oriented headcut erosion model. The model assesses the total time-to-failure of a dike through sequential failure of its components. The following process is simulated. Overflow over a dike causes a turbulent flow along the landside slope, resulting in local damage to the grass cover on either a prescribed weak spot or slope transition. The clay cover is subsequently eroded and the granular core material becomes exposed to the flow. A key assumption in the applied method lies in the fact that every newly exposed layer is less resistant to erosion than the layer above, resulting in slope steepening. Therefore, a near-vertical cliff, referred to as a headcut, is formed. When the overflowing water no longer follows the profile of the steep slope, a cascading flow, resembling a waterfall, forms a scour pit. The turbulent flow in this scour pit also erodes the core material of the dike, allowing horizontal erosion to undercut the slope. The undercutting of the slope causes the headcut to tumble over, moving the headcut and jet impact point to move towards the waterside slope, essentially restarting the scour process. This iterative process continues until the invert height of the dike is lowered to zero and the overflow rate is increased further. Model validation shows good agreement with test results on both large and small scale, as long as the assumptions regarding the structure of the dike hold (a dike profile consisting of a granular core under a clay layer and grass cover). When applied to three case studies, the BRAM-model predicts a similar total time-to-failure as the most advanced current model, posed by d’Eliso (2007). The predicted time-to-failure for the grass cover shows a significant difference. The BRAM-model predicts the grass cover to fail significantly faster than the model by d’Eliso (2007). This difference is offset by a longer predicted time-to-failure of the clay cover. Finally, the proposed model predicts a 50% slower headcut migration rate, as compared to the results by D’Eliso. This is a result of the more advanced description of the headcut erosion process. As the time-to-failure of the headcut migration phase is relatively short compared to the total breach formation process (between 10% and 25%), the total predicted time-to-failure is quite similar between both models. The main advantage of the BRAM-model is its suitability for design testing. The main weakness remains the unpredictable location of headcut initiation, which depends too strongly on spatial variation of the resistance of the dike to be predicted accurately, based on available data. Design parameters to increase the time-to-breaching have been identified. The most relevant were the steepness of the dike slope and thickness of the clay cover. Sensitivity analysis showed that the steepness and thickness of the clay cover, but also the porosity of the core material can be adapted to increase the time-to-failure of a dike. A breach-resistant dike may be designed for a limited overflow duration. Case studies showed three test dikes to sustain an overflow rate of 100 l/m/s for various hours by the grass and clay cover. As soon as the core material becomes exposed, the breach formation process accelerates significantly. The exact duration depends on the profile and construction material of the dike.

Storm safety and durability of touristic destinations is of utmost importance in Cuba, considering high stakes regarding life and capital invested in the development of the touristic sector. This twomonth research focuses on one of the largest Caribbean beach tourism hotspots found in Varadero, Cuba.

Tourism along the Hicacos peninsula has been on the rise and will continue to do so. The Oasis beach hotel is capitalizing on this trend by building a larger new hotel. However, no characteristic flat white coral beach is present in front of it. Tourist demand is greatly driven by the presence of such a beach. Year-round erosion was verified to be partly caused by a blocking of longshore sediment transport.

The local harbour groyne at the eastern beach section was found to be responsible for this but may not be adapted, as it is a necessity for the harbour entrance. Demolition of existing hydraulic structures, construction of a groyne at the westward boundary and sand nourishing are proposed as a zero-solution to ensure sufficient beach width (40 metres) at the 800-metre coastal segment.
Durability is not achieved through this zero-solution as the average lifetime between maintenance nourishments is smaller than one year.

This result shows that successful development of the Oasis beach sector can only be achieved by considering cross-shore erosion processes as well. An important aspect of the cross-shore transport was expected to be the effect of tropical storms on Oasis beach. To ensure the safety of tourists in storm conditions, an assessment of the infrastructure was required.

A multidisciplinary path was chosen to ensure safety of inhabitants, tourists and capital, especially during hurricanes. Flood safety, coastal engineering, transport and infrastructure form the core pillars of the research. Two distinct events were simulated to determine the morphodynamical response of the Oasis beach, namely hurricanes Wilma (2005) and Irma (2017). Both affected the northern coast of Cuba greatly, but passed Varadero from opposite directions. A general hurricane scenario was tested in evacuation assessments of the entire peninsula, which has just one exit road. Furthermore, the capacity of the current evacuation scheme was projected on the expected population and tourists visiting the peninsula in 2048.

Proposed coastal solutions were the construction of a submerged breakwater along the entire length of the beach, an artificial reef or a combination of the two. Normal, cold front and hurricane conditions were imposed upon these structures using XBeach software to test their performance. The subsequent infrastructural safety of the hinterlands was modelled using Simio software.

Results yielded good performance of the artificial reef against structural erosion from both the normal north-eastern wave climate and the northern cold front waves. The submerged breakwater performed better in hurricane conditions though extension of both groynes was found necessary to keep sediments within the Oasis beach system.

A multi criteria analysis was used to determine the best coastal intervention given the project requirements. Initially, no financial motives were used to determine the optimal solution. The results of this analysis stated a preference for the installation of an artificial reef. Its added recreational value was not quantified and thus not discounted from the initial investment. In detailed design, cost estimations of all viable design alternatives showed that the rtificial reef was also a relatively affordable option.

The final recommended design that ensures beach durability thus consists of: demolition of weathered hydraulic structures, western groyne placement, initial nourishment, artificial reef deployment and maintenance nourishment for a 30-year lifetime. A modelling of the definitive design with, also including the vegetation of the dunes indicated the Oasis beach section to be flood safe.

The total cost of this intervention amounts to approximately $900,000 and takes 28 months to complete. If monitored well, the artificial reef will increase its coastal defence capacities and functionality is expected to exceed the 30-year lifetime.

Recommendations regarding storm safety also include the evacuation process of tourists during the extreme hurricane conditions, on which the coastal design was based. Various projections of the growth of the number of tourists on the Hicacos peninsula have been simulated in a Simio evacuation transport model. The model indicated that even for the largest projected growth of tourism in Varadero, the infrastructure suffices and using a 50:50 ratio between evacuees being transported in buses and cars, it is possible to evacuate the peninsula in twenty-four hours.

To be able to evacuate using this optimal ratio, an increase in car ownership in Cuba is required before 2048, as a shortage exists in the current situation. Therefore, the peninsula is still considered storm-safe, but monitoring of the actual increase in tourists is advised.