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Managed Retreat and Coastal Re-alignment



There are times when winning the battle against coastal erosion isn’t possible, or it isn’t actually the best solution to the problem.  The alternative to protecting the coast is to allow nature to take its course, but to still have some control over what happens. This is called ‘managed retreat’, and means that we allow the sea to break through the sea defences and flood the land behind them, but we manage the way in which it happens. The coast moves inland and is ‘re-aligned’, hence the term ‘coastal re-alignment’

The land that’s flooded is usually low lying, was probably previously reclaimed from the sea, and is of low financial value.  It’s cheaper and easier to allow this land to flood than it is to protect it. Although the land owners will have to be compensated for the loss of their land, managed retreat is still much less expensive than protecting the area.

In the UK managed retreat is often the prefered solution when sea levels are rising and the challenge of defending the coast is becomming more and more difficult. Isostatic readjustment after the last Ice Age, and rising sea levels due to climate change pose problems for existing defences that were designed to cope with lower tides. Rebuilding entire stretches of coastal defences isn’t usually practical or cost-effective, so retreat is the sensible option.

Managed retreat isnt all bad new though. By allowing the sea to flood low lying land new mud flatsand salt marshes are created, and these act as natural defences as well as being an important habitat.  Because erosion will resume after the defences have been removed, more sediment can be transported along the coast by longshore drift, allowing beaches further down the coast to be replenished naturally .

Although managed retreat and re-alignment are low-cost and effective, they are not aways popular. People will lose land and possibly buildings, homes and work places too. Areas designated for managed retreat will become unpopular places for development; local authorities may even prohibit certain types of building on the land,knowing that it will be lost to the sea in the future. Because of this the financial value of the land will fall and people who paid good prices for their land will lose out, and expect to be compensated for their losses.

Medmerry Sea Wall

In the UK, a successful example of managed retreat can be seen in West Sussex, where a one kilometer long shingle bank (the Medberry sea wall) , that had been repaired for decades, was alowed to fail.  Every winter the Environment Agency had employed buldozers to rebuild the bank, at costs of around £200,000 every year, to stop the sea from breaching it.

It was necessary to maintain the shingle bank because, behind it, was the only road to Selsey, hundreds of holidays homes, 360 homes belonging to local residents, and a water treatment plant.  The last time the shingle bank was breached, in 2008, resulted in a flood that cost over £5,000,000 in damages, so the coastal defences were seen as vital.


The Environment Agency and the RSPB (Royal Society for the Protection of Birds) had an alternative plan. They suggested building a new sea wall two kilometers inland,on raised land, and allowing the existing defences to fail. This would create a new re-aligned coastline protected by a vast saltmarsh that could absorb the energy from the worst storms and trap sediment as well.

The scheme cost around £28,000,000 which seems expensive compared to £200,000 per year to maintain the existing shingle bank, but the new defences are designed to last for well over 100 years. If sea levels continue to rise as they are now, in 100 years the sea level will be 1m higher and the shingle bank would have become impossible to maintain. Without a large salt marsh zone behind the shingle, and a strong sea wall behind the salt march, disaster could have struck when the shingle bank was finally destroyed.


The map shows the area previously protected by the Medmerry sea wall, and the land behind it that has been allowed to be reclaimed by the sea under the managed retreat and coastal re-alignment project.