Shingle beaches are mobile structures developed in high-energy environments that are very efficient at absorbing and dissipating wave energy. Restoration of shingle beaches on the foreshore can create a more desirable morphological profile that is better able to dissipate wave energy and attenuate storm surge.
Shingle beaches are composed of pebbles or gravel as opposed to consisting only of sand. They can be naturally occurring or manmade and are extremely effective for absorbing and dissipating wave energy and storm surges. Gravel and pebble size varies significantly from 2mm to 200mm. Shingle beaches are typically steep because as the waves flow through and over the coarse and porous surface of the beach, the effect of backwash erosion is reduced creating a steeply sloping beach.
Restoring a shingle ridge
Shingle ridges require upkeep and restoration, particularly after a storm or when the ridge becomes particularly high and narrow. Restoring and repairing a shingle beach is complicated as there are risks relating to ensuring the integrity of vegetation and invertebrates. For example, care should be taken that re-profiling does not reduce the availability of sediment downdrift, potentially increasing flood or erosion risk there.
A wide shingle beach profile will have greater absorption capacity. Historically shingle beaches were made more vertical, putting the shingle ridge in contact with greater wave energy in place a of a naturally expansive shoreline. A steep shingle ridge on the one hand decreases the possibility of overtopping but is at risk of a catastrophic breach in the case of a significant storm.
Restoring vegetated shingle
While composed mostly of rock or pebble, shingle beaches also have a sensitivity to neighboring vegetation. The amount and type of vegetation is largely determined by the stability of the beach and by composition of the finer sediment which can be either sand, silt, clay, or organic matter.
Vegetated shingle habitats are relatively rare as the nutrient bed associated with shingle beaches is often not nutrient rich and are prone to invasive species and weeds. There are however several approaches to restoring vegetated shingle beaches (Forbes et al 2015):
- allowing natural regeneration;
- using the natural seed bank;
- sowing seeds; and
- planting container-grown plants.
The costs of shingle beaches is dependent on several factors. Firstly, if it requires recharge on a short time scale, there will be costs of maintenance. The scale or size of the shingle beach also influences the cost of implementation.
It should also be noted that shingle beaches are effective in storm barriers however they are generally considered disadvantageous for tourism and beach activities.