Dune construction and strengthening

Dune erosion results from wind action (surface erosion) and marine erosion of the toe and face of the dune. Erosion is a natural phenomenon that can be worsened by human activities. Dune construction, strengthening and rehabilitation refer to the restoration of the flood safety and sand reservoir functions of dunes. This include the following processes:<ul><li>Dune grass planting: plant dune grasses on the face of the dune and the front to reduce wind speed across the surface and thereby trapping and holding sand. Planting vegetation helps to stabilise dunes and encourages dune recovery and may therefore be used after storm damage. Alternatively, vegetation may be planted when new embryonic dunes become high enough. In this way a buffer is created at the seaward front of existing dunes which can be eroded during storm surges. In general, the number of plant varieties that can be planted on dunes is relatively small. Selected species must be resistant to silting up, to the wind and to salinity. When the grass cover is established it can become self-sustaining. Regular monitoring and, when needed, re-planting will be necessary.</li><li>Dune thatching: covering the face of the dune with plant debris and branches to stabilise sand, encourage sand accretion and protect dune vegetation. Materials can be put on the ground manually or mechanically. The input of organic material favours the development of plants and grass.</li><li>Dune fencing: construction of fences along the seaward face of the dune to reduce wind speed on the surface and encourage foredune deposition of transported sediment. Fences are often constructed of wood, but depending on local circumstances can also use other material (including, for example, used fish neeting). Dune fencing also can increase the deposit of organic matter and the resulting growth of grasses and other plants. Fences can also act as barriers against wave impact. This technique is not suited for all types of dunes: the installation of fences will be difficult on steep slopes, and in very instable areas. Also, maintenance will be complex in touristic areas welcoming a lot of visitors.</li></ul>These methods are complementary and are usually combined: grass planting usually requires fencing and thatching to succeed. Interventions on dune are more effective when they are integrated with the restoration or construction of the complete coastal transect, including retro-dune wet areas and consolidated dunes with shrub and tree vegetation.Artificial dunes are engineered structures reproducing the form of natural dunes, often in a chain-like manner. They are built with sand brought from an external source area and shaped into dunes using bulldozers, dune nourishments or other means. This is often carried out at the same time as beach nourishment.