effects of rising sea levels
global sea levels have risen on average about 3mm a year in the last 15 years. by 2100, sea levels may have risen a further 30-40 cm. this is enough to submerge low lying places.
causes of rising sea levels:
1. thermal expansion of seawater caused by inbcreasing air temperatures
2. melting continental ice sheets, for example from Greenland, which will add water to the sea
some sections of coastline need to be protected to prevent rapid erosion form the sea, but it is too expensive to protect every stretch of vulnerable coastline. protectiong one area of coast can result in other areas being eroded more quickly or being more likely to flood.
where the sea erodes the coastline it can do so at an alarming rate. this may not be seen as an issue where farmland is involved, but if homes and towns are threatened then it is more serious. there are several common methods used to try and stop erosion
these approaches are usually cheaper and do not damage the appearance of the coast. they are therefore a more sustainable approach to coastal protection. on the other had they are usually not as effective as hard engineering methods.
soft engineering: beach replenishment
sand is brought in to build up the beach either from further along the coast or from offshore. this looks completely natural and provides a beach to protect the coast and for visitors to enjoy. however, the sea will continue to erode the beach so replenishmentr has to be repeated every few years
soft engineering: dune management
sand dunes provide good natural protection for the coast. dunes may be damaged by storms of by visitors walking thorugh them tol get to a beach. dune management includes planting marram grass to stabilise the sand or fill gaps and by making wooden boardwalks for use as footpaths to reduce visitor impact
in some places the sea is being allowed to erode the coast and peopke and activities have to move away. this is clearly the cheapest solution but it is very disruptive for the people who live where land and builings are likely to be lost. in many cases compensation is not paid so individuals can lose a great deal of money. it can be very stressful and disruptive os has important social costs. however, this approach will increase the amount of salt marshes, which help to stop future erosion and flooding and also provide a habitat for birds and wildlife.
integrated coastal zone management (ICZM)
in many areas planners decide to combine hard engineering schenes with soft engineeing and managed retreat. an integraded approach is used on the holderness coast in yorkshire
these structure are very expensive to build and maintain and are only used when towns, villages or expensive installations are at risk and where the economic benefit is greater than the costs involved.
hard engineering: groynes
at seaside resorts wooden walls or groynes are built across the beach to stop the sand being washed away by longshore drift. the beach materials build up at one side of the groyne. trapping material like this may cause problems elsewhere as it stops the material moving down the coast where, for instance, it may be builing up and protecting the base of a cliff. new groynes are expensive and need to be maintained to stop the wood from rotting
hard engineering: sea walls
the most effective method of halting sea erosion. they are also the most expensive and cost about £500,000 per metre to build. made of concrete, they are curved to deflect the power of the waves. but the sea can undermine them if the beach material in front of them is not maintained. sea walls may be unsightly and also can restrict access to the beach
hard engineering: revetments
these are sloping wooden fences with an open structure of planks to break the force of the waves and trap beach material behind them, protecting the base of the cliffs. they are cheaper but not as effective as sea walls
hard engineering: gabions
less expensive than a sea wall or a revetment. they are cages of boulders built up at the foot of the cliff or on a sea wall
hard engineering: rip rap or rock armour
the cheapest method but still expensive. it entails placing piles of large boulders on the beach to protect it form the full force of the sea
hard engineering: off-shore breakwater
these are built on the sea bed a short distance from the coast and are usually made from rock or concrete. they are also very expensive to build but are effective because the waves break on the barrier before reaching the coast. this reduces wave energy and allows a beach to build up, which protects the cliffs
salt marshes: a coastal habitat
salt marshes develop in sheltered river estuaries or behind spits or bars where sediment is deposited. they form where salt water and fresh water meet and where there are no stong tides to wash sediment away. they are covered at high tide but exposed at low tide.
as sediment accumulates it forms mud flats. these are exposed at low tide and colonised by plants may have thick, fleshy or hairy leaves to hold the moisture. cordgrass is a pioneer species often first to colonise the mud; it has long roots to keep it in place. cordgrass helps to trap more sediment allowing other salt tolerant plants to grow. thus the md flats become a salt marsh.