The Northern European Enclosure Dam: A study on the technical feasibility of the enclosure dam

Sea level rise caused by climate change directly affects and threatens low-lying countries. In August of 2021, the report of the IPCC was published, and the findings were disturbing. The sea could rise by a few meters in the coming centuries, causing floods in large parts of West-Europe. Groeskamp and Kjellson proposed a solution to adapt to the effect of extreme sea-level rise, a Northern European Enclosure Dam (NEED). The dam stretched from Bergen in Norway to the north of Scotland and from Ploudalmézeau France to the Lizard Heritage Coast England. The main objective of this thesis is to investigate the technical feasibility of the NEED. To fulfill this objective, the following aspect were studied in more detail: the location and layout of this dam, the favorable cross-section of the dam, and the most likely closure scenarios.The first step was to find out what the optimized location was. The proposed location from Groeskamp was compared to an optimized location based on the boundary conditions. The two alignments are distinguished by their length, depth, and location. An engineering perspective was used to evaluate the alignments. The outcome of the multicriteria analysis (MCA) was that the initial alignment by Groeskamp was most favorable. However, a different perspective can result in a different conclusion, and it is therefore advised to look in further detail to come up with a well-founded decision. For the favorable cross-section, two types of closure dams were investigated to determine the best dam design, the caisson dam, and the earthen dam. Both designs were dimensioned based on safety criteria. These safety criteria were derived from the Dutch guidelines for primary flood defenses, with the top event, inundation of west Europe, given a probability of failure of 1:10 000 per year. A Monte Carlo analysis was constructed to determine the dimensions of both dams. Two failure mechanisms are assessed fully probabilistically as these are considered to be the most relevant. The ULS (ultimate limit state) and SLS (serviceability limit state) conditions are considered per failure mechanisms. The main difference between the resulting designs is the sizes; the earthen dam needs a mild slope to be stable (1:5), requiring a tremendous amount of material. The earthen dam requires seven times more material than the caisson dam. This results in the caisson dam being a more technically feasible design for the NEED than the earthen dam. The caisson is made of concrete filled with sand. Rock protection and concrete foot protection blocks to protect the sill from erosion.The closure procedure depends on the flow velocities inside the closure gap. The occurring flow velocities during the closure determine the feasibility. These velocities were calculated using the shallow water equation. A critical boundary condition for the caissons closure is that the maximum flow velocity in the gap is less than 2.5 m/s. For higher flow velocities, placement of the caissons is impossible. Based on the model, a closure procedure was proposed in which this essential condition is met.The most likely closure scenario is that first, the Southern dam is closed to ensure that the flow velocities do not exceed the critical value. The next step is to fulfill the Northern dam closure. The gap is closed until the maximum velocity is approximately 2m/s. The last part is then closed using sluice caissons. These caissons are placed openly in the gap and closed between 1 tidal cycle, completing the dam. The location of the final gap is at the Norwegian trench.The results from this research are that the NEED is expected to be technically feasible. However, the enormous size of the NEED poses new challenges and effects. Further research is required to comprehensively analyze all impacts of the NEED in order to make it feasible.Civil Engineering | Hydraulic Engineerin