Wallasea Island Case Study: What is the coastal flooding hazard?

Wallasea Island is on the south side of the Crouch Estuary in Essex, which is also linked to the Roach Estuary. Like other estuaries in Essex, these are at risk of flooding because:

  • reclamation of intertidal land has narrowed the estuary channels
  • flood embankments restrict the tidal flow, leading to erosion in the estuary channel and putting pressure on the flood defences
  • on low ebb tides mud is deposited in the channels, leading to a decrease in channel depth
  • sea levels are rising as a result of climate change, putting additional pressure on flood defences so that the chance of breaching and overtopping of defences is increased.

Together these mean there is a significant risk of flooding in South Essex from high tides and storm surges. It was a combination of these that caused the 1953 floods. In a 200-year annual probability flood, Foulness, Wallasea, Potton and Canvey Island would be inundated.

The threat of coastal flooding puts a wide range of assets in the coastal floodplain at risk, including 2,700 properties, 9,500 hectares of high-grade farmland, 168km of flood defences and a variety of natural habitats. Large areas of land are several metres lower than the normal high water in the estuary. As sea levels rise intertidal wetlands and saltmarshes in front of sea defences - internationally important wildlife habitats - are eroded by rising mean sea water levels. This process is known as coastal squeeze.

The Roach and Crouch Flood Management Strategy is used to identify the best way of managing flood defences to help counter the threat of flooding. It is part of the Essex Coast Shoreline Management Plan.

It is clear that that the estuaries cannot be maintained in their present form, and the Flood Management Strategy will ensure the flood defences in these estuaries are managed and improved in an integrated way. The solutions to the increased flood hazard include:

  • hard defences such as sea walls, which will continue to be important to protect towns and cities
  • soft defences such as the managed realignment of coasts, for example the Wallasea Island Project

 

View: Essex Estuarine Strategy

View: Coastal Futures

Download: 'Sea level is not level: the case for a new approach to predicting UK sea-level rise', Roland Gehrels & Anthony Long, Geography, Spring 2008


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