Alternative nourishment methods for the Belgian coast: exploring the possibilities for feeder-type mega nourishments along the Belgian coast
Van De Lageweg, W.I.; Dan, S.; Verwaest, T.; Mostaert, F. (2021). Alternative nourishment methods for the Belgian coast: exploring the possibilities for feeder-type mega nourishments along the Belgian coast. Version 3.0. FHR reports, 14_092_1. Flanders Hydraulics Research: Antwerp. IX, 96 + 30 p. app. pp.
Part of: FHR reports. Flanders Hydraulics Research: Antwerp, more
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Document type: Project report
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| Keywords |
Accretion > Beach accretion > Beach nourishment
Coastal protection > Coastal protection against erosion > Morphodynamics soft coastal defences
Literature and desktop study
Numerical modelling
ANE, Belgium, Belgian Coast [Marine Regions]
Brackish water |
| Author keywords |
Sand engine; UNIBEST CL+; Coastal protection |
Contact detailsProposer: Vlaamse overheid; Beleidsdomein Mobiliteit en Openbare Werken; Vlaams Ministerie van Mobiliteit en Openbare Werken; Agentschap voor Maritieme Dienstverlening en Kust; Afdeling Kust , more
| Authors | | Top |
- Van De Lageweg, W.I.
- Dan, S., more
- Verwaest, T., more
- Mostaert, F., more
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| Abstract |
The natural dynamics of the Belgian sandy coast system are severely disturbed nowadays. The human activities have changed the natural patterns for the sediment transport, which has resulted in accretion and erosion issues along the Belgian coast. The anticipated acceleration of the sea level rise will increase the vulnerability of the Belgian coast to extreme events.
To strengthen the safety of the coast, the Flemish government has approved the Masterplan Kustveiligheid in 2011. This Masterplan consists of a suite of measures to prevent flooding related to a 1000-year flood event. Nourishment of beaches is considered one of the most important measures to maintain and enhance coastal safety. Nowadays, beach nourishments along the Belgian coast (~annual volume 0.5 million m3) are constructed using a traditional method: by heightening the upper and intertidal beach.
A possible alternative for creating a safer and more resilient Belgian coast are feeder-type mega nourishments such as the so-called Sand Engine along the Dutch coast. This innovative soft engineering intervention makes use of natural processes (i.e. waves, currents, wind) to redistribute the nourished sand across the entire coastal profile (i.e. shoreface, subaqueous and sub-aerial beach, and dune area) and represents a paradigm shift in coastal management.
In this exploratory study, quantitative predictions of shoreline change across decadal timescales for a potential feeder type nourishments along the Belgian coast are made. Using the coastline model UNIBEST-CL+, the study aims to i) identify suitable locations for a feeder-type mega nourishment along the Belgian coast, ii) evaluate the alongshore sediment transport post-construction for a range of idealized mega nourishment with varying dimensions (alongshore and cross-shore extent, volume), iii) quantify the dispersion time of these mega nourishment designs, and iv) explore the sensitivity of the predicted shoreline changes and lifespan predictions to the hydrodynamic (i.e. waves and tidal currents) and sedimentary (i.e. grain size and sediment transport formulation) conditions. An identification of the current functions and usage of the Belgian coast is firstly made. By mapping opportunities from the coastal protection perspectives, nature development and recreation, an overview of the preferred locations for a feeder-type mega nourishment is generated. To address the multi-functionality of a mega nourishment, a location in which as many functions as possible can be combined is preferred.
Then, thirteen idealized nourishments are listed. The nourishments have a seaward extent ranging between 150 m and 900 m with variable alongshore lengths to evaluate the effect of geometry on resultant shoreline changes. The smallest nourishment has a volume of 1 million cubic meter of sand and the largest one is 30 million cubic meter. Using UNIBEST-CL+, all nourishment designs show a morphological reshaping from the original trapezoidal shape to a smoother bell shape during the first years post construction. As a result of the reshaping, the seaward head of the nourishment retreats and sand is being fed to the adjacent beaches, leading here to coastal advance. A key finding is that the dispersion time scales approximately linear with the initial nourishment volume for the same width-to-length ratio. A cost-effectiveness analysis indicates that a feeder-type mega nourishment should be considered a tool of opportunity for Belgian coastal managers. The tool can be employed when sand is available at a low cost relative to the regular nourishment program, and when the interest rate is low relative to the decadal average. When sea-level rise is taken into account, the required sand volumes will increase and the cost-effectiveness improves. |
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