Initial volume losses at nourished beaches and the effect of surfzone slope.

Nourishment projects often experience a period of large initial losses just after completion of the project. A better understanding of these losses would improve the design of nourishment strategies. Here we propose that the large initial losses could partly originate from the change in the cross-shore slope. A steepening of the slope results in an increase in background erosion, as is deduced from common bulk sediment transport formulae. Morphological data from a nourishment at Vlugtenburg Beach, the Netherlands provide support for this hypothesis. At Vlugtenburg we observe a large difference in the erosion rates between the first years. Our measurements also show that the slope adjusts on similar timescales as the timescales of initial losses, i.e. 1 to 2 years. We conclude that the steepness of the man-made profile is an important parameter, which may be manipulated to influence the lifetime of the nourishment.