Interdependence of Beach Fill Volumes and Repetition Intervals

Shore protection by beach nourishment is an environmentally favored method but is dependent on the availability of sand and its cost. Therefore, in order to save on cost and sand resources it is essential to keep the annual sand requirement for nourishment to a minimum. A theoretical model of a two‐dimensional infinitely long, straight beach is presented that links the nourishments volume (m³/m) with its decay due to losses and the intervals between beach nourishments with the required volumes. The results show that the average annual sand requirement is at its minimum when the nourishment is continuous, e.g. grain by grain according to demand. With increasing intervals the required annual nourishment volume increases rapidly. The corollary is that the sand requirement can be reduced by using smaller fill volumes at shorter intervals. In practice this means that an optimization of the sand requirement becomes a compromise between frequency of nourishment and the annual sand demand. The model shows that the sand requirement can be significantly affected by the beach fill volumes and the intervals between nourishments. Field data show that the model describes the sand‐loss rate to about half‐life of the fill. With increasing time the loss rate approaches a lower value. This lower loss rate may represent the “undisturbed” regional loss rate.