Flanders Bays on Belgian North Sea Coast: Smart Beach & Dune Nourishments to Achieve an Integrated and Sustainable Reinstatement of Beach Barrier Systems
Type:
Presented during:
WODCON XX: "The Art of Dredging" - 2013, Brussels, Belgium
Authors:
Malherbe B, Fordeyn J, Defloor D
Abstract: The 67 km long Belgian North Sea Coast is a recent sand-barrier coast, consisting of a narrow dune and beach belt, which is the primary natural defence system against flooding of the 200.000 ha of coastal-plain lowlands, commonly called the “polders”. For about a century both waterfront and polder- lowlands knew an intensive urban and resort development, combined with hard coastal defence structures and protruding seadikes, turning it into a “squeezed coast” with little or no space left for any ecological, economical or residential developments anymore. Moreover, a large part of all 240 coastal sections are subject to structural erosions of beach and dune systems resulting in an insufficient flood protection against extreme storm-events.
In the same period, it appeared that the old-tech “hard coastal protection systems” – seawalls, groynes and revetments – have proved a poor efficiency, if any, in achieving a sound coastal protection, being unable to deliver safety against flooding. Moreover, these cannot be considered as sustainable anymore, because they don’t cure the cause and are not capable to integrate the unknowns about future climate change and sea-level rise.
The main cause of the poor sedimentological health of the beach and dune barrier in the erosive sections seems to be a chronic shortage of sand in the system. This shortage of sand causes the seaward-slope to progressively steepen, and prevents the free play of the coastal morpho-dynamics which provides the resilience for coastal protection. Protruding seawalls and shrinking sand-reserves in the system result in a “squeezed coast”.
In the early 90-ies, a first “morphological beach and dune restoration “ was executed, which proved to be a costefficient and sustainable solution for the 10km long coastal stretch centred around De Haan. This large full-scale coastal protection scheme – unique in its kind – inspired the concept for a safe and streamlined coastline as part of the vision –plan ‘Flanders Bays’: it integrates various functions of the beach, including extreme storm-event response and resilience, touristic beach developments, drink and food facilities, ecosystem functions, eventfacilities,… etc. The engineering design of these “smart beach and dune nourishments” is based on the observation of natural morpho-dynamics and achieved reclamations and by replicating these natural processes: a replica of the beach morphology and the natural beach sand.
Basically a “smart beach and dune nourishment” consists of:
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A “shore-face nourishment” with which the LW-breaker bar is reclaimed in order to tackle any further steepening of the sub-tidal beach and the sand-demand of the submerged part of the beach; the selected sand-granulometry for reclamation is compliant with the original sand of the Low Water -breaker bar;
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A “profile nourishment” of the tidal beach between Chart Datum + 1m and Chart Datum + 5m, in which the sand is profiled in compliance with the anticipated equilibrium slope of the beach in order to minimise resuspension and subsequent losses due to tidal and wave-induced currents; the selected sand –granulometry for reclamation is compliant with the original beach-sand ;
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A wide “upper-beach platform” at CD + 8m, above storm-surge level, prevents any form of whitewater or blue-water wave-overtopping, providing a buffer for extreme storm-event flash-erosions and a platform for various beach developments
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Flexible and removable wind-screens on the supra-tidal beach in order to capture/fix the eolian sand during the winter months.