Artificial coastal sand nourishments are applied for various reasons:
- to compensate losses due to (structural) erosion, and hence maintaining biodiversity
- to enhance the safety of the hinterland against flooding
- to broaden a beach or create new beaches e.g. for recreational purposes
- to reclaim new areas such as peninsulas or artificial islands for urban or industrial development
- to feed the surrounding coast with sand at a rate governed by nature
In the case of structural erosion, the nourishment will have to be repeated from time to time as the erosion is an ongoing process. The interval between successive nourishments depends on the rate of erosion and on the equipment mobilization costs. In addition, the timing of the nourishment should be carefully chosen with respect to breeding season of species (seals, birds, etc.) and nursery habitats of fish and shrimps. Generally, an interval of five years is considered acceptable (for Dutch cases). Compared to hard solutions, nourishments must be repeated from time to time, hence it is flexible, while costs are spread over a longer time. For conditions along the Dutch coast this makes the soft nourishments more economical than the hard solutions with the added advantage that no lee-side erosion occurs (typical for hard solutions).
Sand nourishments can be carried out at various locations in the profile, such as the shoreface or foreshore (underwater), beach & surf zone and in the dune zone. In alongshore direction, the nourishment can be distributed over a large distance or placed more locally (concentrated). In the latter case, the goal of the nourishment could be to feed the adjacent coast gradually. Tide, winds and waves transport the sediments and spread it along the coast. This distribution of sand occurs gradually at rates that the adaptation of nature and species can keep up with. This enables nature and species to adapt. In case of an emerged nourishment, where part of the nourishment reaches above high water level, one can speak of a concentrated nourishment feeding the surrounding coastal area: e.g. the new beach provides new services such as recreation. A very large submerged foreshore nourishment does not provide such services; thus, for additional service for coastal development it is important that part of the nourishment is emerged and accessible (either by foot or boat). In case of an emerged concentrated nourishment the length of the shoreline increases due to the nourishment providing more space for recreation, water sports and beach lovers. In addition, new dunes and vegetation could develop increasing nature value.
Nourishments for coastal development attracts new services and hence new beach visitors (human and animals), which require a different management of the coast at the nourishment and its surroundings. In case of an unprotected nourishment, the shape and bathymetry of the nourishment will change continuously under the forcing of tide, wind and waves. It is therefore important that an adaptive management strategy is adopted to anticipate on unforeseen and poorly predictable developments.
Shallow areas in front of hydraulic infrastructure act as a buffer for safety by dissipating wave energy. Due to the extra segment of water that is created by the rise in sea-level, a sediment shortage on many of such shoals will be created leading to a decrease in area. Nourishments can be an effective measure to fulfill the sediment demand of the shoals and maintain a dynamic equilibrium between erosion and sedimentation.