Coastal Erosion is defined as the weathering of rocks, removal of beach or dune sediment as a result of wave action, tidal currents or drainage.
Coastal erosion events are driven by storm events and sea-level, amongst other factors. The KZN coast sees regular erosion on a normal spring tide, the effects of which are often exacerbated by a reduction in sediment supply. KZN is seeing a regional sand deficient, due to drought, sand mining, dam construction and unwise coastal development. In addition protection measures such as breakwaters and groynes can block the flow of sand leading to accreting beaches to the south of the structure, while beaches to the north continue to erode.
Sections of coast considered vulnerable to erosion include:
- Narrow, sand depleted beaches and bays,
- Sandy bays which are north of points,
- Beaches with a thin veneer of sand over rock,
- Beaches whose natural defence mechanisms such as foredunes, naturally vegetated dunes, offshore sand bars and reefs have been removed,
- Beaches with, and adjacent to, inappropriate sea defences,
- Beaches where the built environment is located too close to the high-water mark, and
- Beaches with badly planned, inappropriate and poorly maintained stormwater systems.
The main management concern often relates to impacts on the built environment, public and private property and effects of livelihoods.
In order to fully understand the seasonal and long-term effects of coastal erosion along the KZN coast, ORI and EDTEA has established pilot monitoring programmes for sections of coast in order to track erosion rates and recovery. Data collection for this project is ongoing and results will be made available in due course.
What can and cannot be done to prevent future erosion?
- Determination of coastal management lines will ensure that development does not occur too close to the high-water mark, thus preventing further interference with natural sand movement.
- Prevent the removal of sand from beaches; eg. Sandmining.
- Consider green engineering in the design of sea defences, as hard engineering will result in further loss of sand.
- Maintain and rehabilitate natural dune vegetation, this assists in stabilising the frontal dune which in turn will offer protection against storm surge and erosion.
- Main problem is not enough sand delivery to the coast and then offshore.
ORI • EDTEA