Coastal vulnerability index (CVI)

The coast at Happisburgh, Norfolk.

The mainland of Great Britain is surrounded by over 11 000 miles of coastline. It is a very diverse coast both in terms of geology and geomorphology, ranging from the high chalk cliffs of Sussex to the flat expanses of The Wash and Morecambe Bay.

Our fragile coastline

The coast has been shaped by the continual forces of erosion from the wind, waves and tide, and the characteristics and composition of the coastline will dictate the degree of its vulnerability.

This has been starkly demonstrated by the winter storms of 2013–14, which resulted in widespread damage to infrastructure, such as the main line railway at Dawlish and undermining of properties along the Norfolk coast at Hemsby.

With climate change forecasts of an increase in the frequency and intensity of winter storms, the BGS is developing its coastal vulnerability index (CVI), drawing on existing BGS datasets and expertise and working in collaboration with other organisations to help manage these changes in the future.

The coastal vulnerability index

CVI version 1 showing the area around Llandudno.

The CVI will offer anyone with assets or an interest in the coastline around Great Britain access to easy-to-use datasets linked to geohazard data. This will allow users to interpret potential interdependencies in terms of erosion, flooding, habitat and other vulnerabilities. Version 1 of the CVI represents the natural geological coastline (around the mainland of England and Wales) as if no coastal defences or made ground are present. This will be of particular value in areas where coastal defences are no longer maintained. Subject to availability, it is anticipated that future versions of the CVI will include all coastal defences and made ground.

CVI layers

Backshore

The backshore layer is derived from an analysis of the cliff stratigraphy around the coastline of Great Britain. Three engineering geology properties (strength, permeability and discontinuities) for each geological unit are assessed using an algorithm to produce an erosion susceptibility score.

Discontinuities within the cliff have an effect on the physical strength of the geological units.
Discontinuities within the cliff have an effect on the physical strength of the geological units.
Discontinuities within the cliff have an effect on the physical strength of the geological units.

Foreshore

The foreshore and wave–cut platform at Dunraven, South Wales.

The foreshore layer contains the spatial extent of coastal geomorphological features (beaches, tidal flat deposits, saltmarshes or wave-cut platforms or any combination of these) that would potentially act to dissipate wave energy before it meets the cliff. These features would effectively 'buffer' the cliff or backshore and potentially decrease rates of erosion from waves and currents. Any feature over 100 m in width has been included.

Cliff height

The cliff height layer consists of cliff spot heights in metres spaced at 50 m intervals, sampled from NEXTMap around the Great Britain mainland coast.

Inundation

The inundation layer shows the potential for coastal inundation based on a combined analysis of the existing BGS groundwater flooding and geological indicators of flooding (GIF) datasets, the rationale being that, during an extreme storm event, coastal flooding will likely be exacerbated by groundwater flooding. This dataset is intended to complement the Environment Agency flood maps.

The inundation layer
The inundation layer
The inundation layer

Focus group

Seepage erosion above clay aquitards, Isle of Wight

A focus group was initiated from the inception of the CVI to ensure that the product met the needs of stakeholders. Trial datasets were released to members of the group for comment as it becomes available.

If you are interested in joining the focus group please contact Katy Lee.

Future work

Future versions of the CVI will contain:

  • coverage for Scotland and the islands around Great Britain
  • integrated oceanographic data in collaboration with the National Oceanography Centre (NOC)
  • a dominant failure mechanism layer: an overview of the types of coastal landslides (e.g. rotational landslides, rock falls) present around the coastline of Great Britain
  • attribution of the foreshore layer
  • coastal defences and made ground

Contact

Contact Katy Lee for more information.