Due to accelerating climate change, which entails more extreme storm conditions and exponential sea level rise, the protective function of our dikes and levees is under growing pressure. The presence of so-called forelands (e.g., beach, mudflat, and tidal marsh) are promising Nature-based Solutions to reduce the probability of dike failure and to mitigate the consequences after a dike breach. However, the positive effects of forelands depend, for instance, on sediment composition, geometry, and the presence of vegetation. These effects have not been studied in detail and have not been incorporated into reliable physical and validated mathematical models yet.

This report describes an experimental study on the stability of different foreland types. Particularly, the following aspects were considered: investigating whether surface and headcut erosion are indeed the dominant foreland erosion mechanisms, plus providing experimental data for validation purposes for models such as the extended BRES model.

Twelve experiments were performed in the sediment flume facility of the Hydraulic Laboratory of the faculty of Civil Engineering and Geosciences at the Delft University of Technology. A foreland during breaching conditions (i.e. high flow velocities) was simulated by an experimental setup, a so-called broad-crested weir. This weir was developed, constructed, and built within the facility to simulate and study erosion processes of two foreland sediment types, sand and clay. Geotechnical properties were obtained by performing sediment analyses in the Geoscience and Engineering Laboratory. In order to try to exclude the influence of cracks, a special adjustment of the facility was made by covering the sediment package with plywood panels; these experiments are referred to as ‘Tompouce’. For collecting data, the facility was fully instrumented with hydraulic sensors (discharge, flow velocities, and water levels) and synchronized cameras. The erosion process was analyzed and quantified from the visual data.

The experiments enabled us to answer the main research question, “Which erosion mechanisms are important to consider for forelands under dike breach conditions?”. For non-cohesive sediments, surface erosion should be considered the dominant erosion mechanism. In the case of cohesive sediments, however, headcut block erosion should be considered the dominant erosion mechanism. Here, when cracks are present, the erosion rate increases considerably. Especially the latter effect is a new finding; this mechanism should be included in foreland-dike breach development modeling. More research is needed into the quantitative effect of cracks on the stability of a vegetated foreland when it is subject to (sudden) high-water events.
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What long ago started as a small fishing village, seeking refuge from the Romans, slowly evolved into the city of Venice that we know today. With its unique location came unique problems, most of which were related to the interplay between Venice and its lagoon. By severe measures in the past it has continued to withstand the test of time.
In the decades to come, Venice, once again, has found itself in a difficult situation. Like has been done in the past, drastic measures are required to deal with the current and upcoming difficulties threatening the survival of Venice. These difficulties range from over-tourism to sea-level rise and the subsiding of the city. Acting like the Magistrato alle Acque acted in the past, extreme visions where laid out as possible solutions to these threats.
A workshop week with focus on interdisciplinary design formed the basis for two extreme visions which are laid out in this report. With the aim of answering the main research question: How do flood defense systems influence the spatial aspects of the territory in the context of a high dynamic landscape in the Anthropocene?
The plan for the Perfect Lagoon is one of these, which has focuses on tackling all of the current and upcoming problems were the emphasis lies on preserving and perfecting the lagoon using the building with nature philosophy, while also saving the city from drowning. Preservation is done by solving the sediment budget problems. Due to the constantly eroding system, salt marshes and land is slowly disappearing.
In this plan, drastic actions will be taken to counteract the constant erosion as well as the effect that sea level rise will have on this unique estuary. Drastic measures like redirecting rivers and re-purposing the MOSE contribute towards this goal.
After preservation comes restoration as one of the goals is to restore and increase ecological value, restoration of salt marshes and removal of negative influences like pollution.
As a second vision, the plan of the Symbiotic System deals with the same problems but here the emphasis lies on interconnectedness of Veneto. More attention is paid to mass tourism. The plan aims to turn Venice into a modern interconnected metropolitan area. The city and the lagoon will be treated as two separated system where the focus lies completely on the city of Venice. The lagoon will be left to its own devices in order to find a new, still unknown, equilibrium.
These visions are then further worked out and explained, and for both visions, technical design are made to, step-by-step, bring these visions closer to reality. From these visions along with their technical design we can conclude that flood defence systems have a major influence in the spacial aspects of the territory. Not only in its primary function, but more importantly in the secondary functions. Both primary and secondary functions can be used to create a paradigm shift for the territory. Using the multidisciplinary approach, an integral design can be made for the flood defence, in which the opportunities in a territory can be maximized. ... Read more