In 1990 the Dutch government passed legislation that dictates the South West Texel coast must be maintained with regard to the 1990 coastline. The coast is currently maintained by applying shoreface and beach nourishments with an interval of approximately 3 years, because it experiences erosion. The problems with this approach are that the mobilization of the dredging vessels is expensive, dredging vessels cause nuisance in the ecological system and moreover, the dredging vessels emit carbon dioxide and therefore contribute to climate change. The first goal of this study was to to investigate if an alternative coastal protection strategy is able to mitigate the drawbacks of the current scheme. Consequently, the application of a mega nourishment was chosen over a cross-shore dam or an outer delta nourishment. To optimally design a mega nourishment, a morphological analysis was executed that focused on elements in the sediment balance of the system. Using Vaklodingen and JARKUS data, volume changes of each transect were identified for 4 parts of the transect: the dune, the beach, the shallow part of the foreshore and the Molengat channel. It was found that dunes started growing from the moment that the nourishments were structurally applied. When nourishments are aborted, it is expected that the shrinking of the dunes will resume, just like the pre-1990 situation. The Molengat in the transects was found to be moving towards shore before the nourishment program started, and its landward movement was not influenced by the implementation of the nourishment program. The Molengat filling rate was projected into the future, leading to a fill date in transects 880-930 by 2035, and in transects 930-1013 by 2055. In transects 1013-1108 and 1108-1210 the Molengat has already been filled. The late projection filling date of transects 930-1013 is a reason to put the mega nourishment at that location, combined with the largest natural erosion occurring at the same location. The application of a mega nourishment is done by putting 20 years worth of sediment at transect range 945-1053 in one construction project. Simultaneously, the mega nourishment aims to diffuse sediment alongshore in the shallow part of the transects, providing sediment to adjacent transects. The sediment supply to other transects could be able to limit the shrinking of the adjacent dunes, or even let them grow. However, this requires further investigation. Delft3D Model results showed that sediment transport in this area is mainly caused by waves on the NUN-shoal, and by the current in the Molengat ebb-tidal channel. The model resolution was not fine enough to accurately describe the accretion and erosion patterns alongshore. Yet, by the use of results of morphological updates it could be determined that the mega nourishment will likely cause accretion south of the nourishment area. This research can be used as a stepping stone for future design steps of a mega nourishment, and also for acquiring knowledge about future behaviour of different parts of the bottom profiles in the South West Texel area.
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The coastal area of the Murcia region in Spain experiences more frequent and more intense flash floods caused by inland heavy rainfall due to climate change. This results in high water levels in towns and cities, leading to risk of loss of life and many financial damages. Currently the region is vulnerable, because there are no hydraulic structures that regulate the flow safely downstream towards the coastline. Instead, at this moment the current channels are inadequate dry rivers. To reduce the risk of flooding, the objective of this design was to design a flood abatement control zone (ZAC). This design followed the design approach for Hydraulic Engineering.

A ZAC consists of a series of dikes that enclose separate reservoirs that are able to temporarily store water. This dampens the peak discharge of the flash flood, which reduces the flood risk of the downstream area. The peak reduction is the main function. The water that is stored is being discharged with a delay, spreading an acceptable discharge over a longer time to discharge the same rainfall event volume.

The first step of the design was to define the system of the ZAC. The ZAC was combined with the creation of an up- and downstream channel with short lengths to fit the structure into the environment. Its design life was set at 50 years, corresponding to a design rainfall event of once per 474 years. To design this structure, it was important to determine the maximum rainfall event discharge and the existing maximum discharge capacity without floods occurring downstream. These 2 factors, together with soil properties and land boundaries, acted as boundary conditions to the system.


In step 2, two locations were considered as potential construction location, both indicated by the client Universidad Polytechnica de Cartagena (UPCT). By applying a multi-criteria analysis (MCA) based on predominantly the water inflow, potential storage area, close company buildings and houses, the more upstream location was chosen.

Step 3: in order to design an adequate ZAC, a model was required to create the before-and-after-construction situation. A hydrological 2D-flow model was created in HEC-RAS. This was closely tied to functional design and design steps were taken iteratively. The 2D-model was able to compute flow in longitudinal and lateral direction, which is strongly needed in a flooded terrain. The most important design parameters to test in the model were the culvert-spillway-structure and the number of reservoirs. The model was validated qualitatively by flood maps from Centro de Descargas del CNIG.

Then, the functional design of the ZAC was done in step 4. The ZAC was placed partially dug into the soil upstream, and partly sticking out of the soil downstream. Upon iteration, it was decided to create 5 reservoirs, because of costs and a smaller marginal peak reduction effect of extra reservoirs. The ZAC is created in combination with a downstream funnel, downstream outflow channel and upstream channel. This means that the reservoirs are enclosed by 2 side dikes and 6 lateral dikes.

Then, detailed design in step 5 followed. The culvert-spillway structure was designed. The aim of this structure is to let water through the reservoirs without overflowing and therefore damaging the dikes. The structure consists of a culvert, spillway and retaining walls. For each element an MCA was set-up to determine the optimal shape, followed by choosing the design alternative. The design is a trapezoidal spillway, an arched culvert and a retaining wall.

With the optimal design, a conceptual design is constructed. In this conceptual design, the reinforced concrete dimensions and governing load combinations are determined. From this, the strength of the ZAC structure is evaluated in the finite element method program DIANA.

Finally, the final design was created. The conclusion is that the combination of structural elements that have been modelled in the system satisfies the aim to reduce the design rainfall event flood wave enough to avoid flood risk to the downstream areas of Murcia. The main uncertainties are the scaling of the data of the design rainfall event and the used soil characteristics. Further research could look into quantitative validation of the 2D-flow model, the implementation of sediment transport in the model and into optimizing bed protection downstream of the ZAC. ... Read more