30 / 09 / 2019
Beach cliffs after a storm on a Belgian beach. Photo: René Billiau
After just about every winter storm, so-called ‘beach cliffs’ appear on numerous beaches of the Flemish coast (Belgium). And every time a lot of criticism is heard. On the one hand, these cliffs pose a safety risk for passers-by. On the other hand the impression is created that beach nourishments are uselessly "carrying sand to the sea". New Flemish research results of the four-year CREST project (www.crestproject.be) show that these beaches recovers partly spontaneously in the following months after a storm. At the same time, the sand suppletions contribute to a strengthening of the dunes by wind-driven sand transport, and they offer a protective buffer for the sea dikes against wave violence. "That is good news. Now it is confirmed by figures that the coastal protection approach, as it is applied today, works: soft (sand reclamation) where possible, hard (dikes, storm walls, etc.) where necessary," says Professor Jaak Monbaliu, coordinator of the CREST project. “By supplementing the beaches after storm events, the government can maintain a strong coastal foundation in the most natural and most cost-efficient way. Spontaneous feeding of sand from the sea has also contributed to the preservation of this coastal foundation in the past thirty years.”
This research also confirms that wider beaches buffer the impact of incoming waves on the sea dikes and that a significant part of the nourished sand finds its way to the dunes, the natural coastal protection par excellence. On the lower beach, waves and currents play a major role in redistributing the sand; higher up, the wind (the so called aeolian sand transport) is the steering factor. Measurements demonstrate that the dunes have grown on average by 6.2 m³ / m / year over the past decades, mainly under the influence of aeolian sand transport from the beach with W-SW winds.
Various technologies for monitoring the beach morphology have proven their worth within the CREST project. The study of the more fundamental, underlying processes proved to be a good basis to the understanding and simulating the sand displacement patterns of on the Flemish coast. Experiments in the test facilities of Ghent University, the Flanders Hydraulics Research and Deltares contributed significantly to estimating the power of waves on hard structures. In addition, CREST developed the FLIAT model as a solid basis for flood calculations of the hinterland. This instrument can be of particular value in the long term with a further rise in sea level and an increasing risk of flooding.
In the CREST project ten institutes from academia cooperated with the Flemish government and the private sector. The consortium have built up a great deal of knowledge about coastal processes in the past four years. The project is part of the Strategic Basic Research (SBO) program of the Agency for Innovation & Entrepreneurship, and ends on 31 October 2019.
The project led to nine key messages, and a compact list of striking results for each of the four themes examined. Download the compact final report.
Contact at VLIZ for the CREST project: tina.mertens@vliz.be