IMIS

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.