Coastal defence

Populations by the coast are forever increasing. However the sea is constantly eroding beaches and cliffs, moving further inland towards these centres of human activity. Miami in Florida, USA, has miles of beachfront property and businesses, and as the sea advanced seawalls (?hard engineering?) were constructed to protect inland communities. However this defence does not curb the rate of beach erosion, in fact, the sea defences bounce the wave energy back out onto the beach, accelerating erosion. An alternative ?hard engineering? sea defence to basic coastal walls is a ?groin?. This is a rock wall perpendicular to the beach that gathers sand on the updrift side of the wall because the longwave action is slowed and slower moving water allows suspended particles, ie sand, to displace and accumulate. However detrimental effects are seen at the downdrift side of a beach, where the sand gets displaced from. Miami beach property owners have resorted to the expensive task of pumping sand onto their beaches. A process that will need repeating continuously as the sea never fatigues of eroding beach away.

Unfortunately sea defences, hard engineering sea defences in particular, do cause the displacement of large areas of wetland habitat that is essential for birds, benthic life, commercially important fish populations and acts as a sink for both marine and river-borne pollution, breaking down pesticides, nutrients, PCBs (polychlorinated biphenyls) and heavy metals. An offshore alternative is to dump long heaps of rocks, or even tyres, parallel to the shore that act as man-made coral reefs, intercepting waves, reducing wave action, and subsequent beach erosion. 6000 of these have been erected along Japanese coasts. These offshore structures are new areas that many plants and animals can exploit but they act as physical boundaries that can hinder the movement of larger marine creatures such as dolphins, rays, and porpoises. A ?soft engineering? initiative, with far less environmental impact, is to allow coastal areas to revert back to wetland habitat.

Some areas of high economic value along English shores, such as centres of tourism, are at risk coastal erosion. In March 2002, Scarborough on the Northeast coast of England received �28 million of aid to help combat the effects of coastal erosion and protect the homes and businesses at threat.

Another aspect to consider is that as global warming takes its hold on the planet the sea levels are expected to rise. This will naturally increase coastal erosion, and against a global onslaught of this kind, sea defences shall probably not be sufficient.