Updated:
Thursday, September 8, 2005 10:02
People have tried to control erosion and flooding for many hundreds of years, with varied success. There are a number of alternatives when there is an erosion or flooding problem
1. Do nothing
2. build sea walls etc at the edge of the sea
3. build forward e.g. groynes, beach nourishment
4. build off shore defences e.g. offshore bars or breakwater
FACTORS TO CONSIDER
1. Cost of the scheme and up keep costs
2. Benefits of the scheme e.g. homes, farmland, roads and lives
3. How effective is the scheme
4. What effect will it have on other areas
5. What will it look like
6. Who pays. In low-lying areas the N.R.A. is responsible and in high areas
it is the local council. The government will give a grant if it accepts that
the scheme is needed.
| DEFENCE | COST | ADVANTAGES and DISADVANTAGES |
| Sea wall | £6000 per m | Very strong,but may reflect waves,causing turbulence and undercutting . Very expensive |
| Rock revetment | £4500 per m | Absorbs the energy of the waves. Over time the rocks break up. Unsightly |
| Offshore bar | £5000 per m | Protects the base of the cliff. Must be large rocks or will be moved by storms |
| Groynes | £5000 each | Trap sand if there is any to trap. Steal sand 100m apart from beaches downdrift increasing erosion |
| Beach nourishment | £3500 per m | Absorbs wave action. May need replacing |
SHORELINE MANAGEMENT PLANS
Until recently coastal management plans were piecemeal. Each area looked after its own part of the coast, which caused problems for adjacent areas. In 1995 MAFF encouraged the development of a more integrated approach in the form of SMP's/ They are made of sediment cells e.g. the coast from Hengistbury Had to Hurst Castle spit in Hampshire.
Stage 1 Collect data about processes and defenses, land use and ecosystems
Stage 2 Management objections set.
Stage 3 Plan preparation & Consultation.
Stage 4 Review.
MANAGED RETREAT OF THE COAST
In the past high flood tides and surges were absorbed by salt marshes along the coast. Over the years, these areas were reclaimed to create fertile farmland e.g. in the Fens, Romney Marsh and Pett Level, Thames Esturary, polders of the Netherlands etc. This was seeen as very important after the food shortages of the Second World War.
From time to time these areas are flooded by the sea, and have been protected by higher and higher sea walls and other defences . As sea level rises owing of the Greenhouse effect it will cost increasing amounts to protect this land. There has been a food surplus in the EU recently so the fertile land is less highly valued. In some places managed retreat is being used.
This allows part of the sea wall to be destroyed and the land behind is flooded during high spring tides until it reverts to salt marsh. This takes about 50 years. This land is seen as being expendable.
Updated:
Thursday, September 8, 2005 10:02