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The influence of groin fields and other hard defences on the shoreline configuration of the soft cliff coastlines

The influence of groin fields and other hard defences on the shoreline configuration of the soft cliff coastlines
The influence of groin fields and other hard defences on the shoreline configuration of the soft cliff coastlines
Building defences, such as groynes, on eroding soft cliff coastlines alters the sediment budget, changing the shoreline configuration adjacent to defences. On the down-drift side, the coastline is set-back. This is often believed to be caused by increased erosion via the ‘terminal groyne effect’, resulting in rapid land loss. This paper examines whether the terminal groyne effect always occurs down-drift post defence construction (i.e. whether or not the retreat rate increases down-drift) through case study analysis.

Nine cases were analysed at Holderness and Christchurch Bay, England. Seven out of nine sites experienced an increase in down-drift retreat rates. For the two remaining sites, retreat rates remained constant after construction, probably as a sediment deficit already existed prior to construction or as sediment movement was restricted further down-drift. For these two sites, a set-back still evolved, leading to the erroneous perception that a terminal groyne effect had developed. Additionally, seven of the nine sites developed a set back up-drift of the initial groyne, leading to the defended sections of coast acting as hard headland, inhabiting long-shore drift. Set-backs can also develop if defences are selectively removed along a heavily defended coastline, as found in an additional study site at Happisburgh, Norfolk.

Four possible post defence coastal configurations are presented, designed to support strategic shoreline management. Defences might not always be responsible for increased down-drift erosion, which has potential implications for shoreline management and litigation. Selective defence removal leading to changes in coastal configuration may become more common in the future.
southern and eastern england, historical shoreline analysis, cliff retreat rate, set-back, terminal groyne.
0037-4237
13-24
Brown, Sally
dd3c5852-78cc-435a-9846-4f3f540f2840
Barton, Max
eea85a67-8def-49a1-a48c-f332310388d9
Nicholls, Robert
4ce1e355-cc5d-4702-8124-820932c57076
Brown, Sally
dd3c5852-78cc-435a-9846-4f3f540f2840
Barton, Max
eea85a67-8def-49a1-a48c-f332310388d9
Nicholls, Robert
4ce1e355-cc5d-4702-8124-820932c57076

Brown, Sally, Barton, Max and Nicholls, Robert (2016) The influence of groin fields and other hard defences on the shoreline configuration of the soft cliff coastlines. Shore and Beach, 84 (2), 13-24. (In Press)

Record type: Article

Abstract

Building defences, such as groynes, on eroding soft cliff coastlines alters the sediment budget, changing the shoreline configuration adjacent to defences. On the down-drift side, the coastline is set-back. This is often believed to be caused by increased erosion via the ‘terminal groyne effect’, resulting in rapid land loss. This paper examines whether the terminal groyne effect always occurs down-drift post defence construction (i.e. whether or not the retreat rate increases down-drift) through case study analysis.

Nine cases were analysed at Holderness and Christchurch Bay, England. Seven out of nine sites experienced an increase in down-drift retreat rates. For the two remaining sites, retreat rates remained constant after construction, probably as a sediment deficit already existed prior to construction or as sediment movement was restricted further down-drift. For these two sites, a set-back still evolved, leading to the erroneous perception that a terminal groyne effect had developed. Additionally, seven of the nine sites developed a set back up-drift of the initial groyne, leading to the defended sections of coast acting as hard headland, inhabiting long-shore drift. Set-backs can also develop if defences are selectively removed along a heavily defended coastline, as found in an additional study site at Happisburgh, Norfolk.

Four possible post defence coastal configurations are presented, designed to support strategic shoreline management. Defences might not always be responsible for increased down-drift erosion, which has potential implications for shoreline management and litigation. Selective defence removal leading to changes in coastal configuration may become more common in the future.

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More information

Accepted/In Press date: 4 April 2016
Keywords: southern and eastern england, historical shoreline analysis, cliff retreat rate, set-back, terminal groyne.
Organisations: Energy & Climate Change Group

Identifiers

Local EPrints ID: 393174
URI: https://eprints.soton.ac.uk/id/eprint/393174
ISSN: 0037-4237
PURE UUID: 364c4ef4-a5bf-4157-bd0b-7ecf3dcdbcae
ORCID for Sally Brown: ORCID iD orcid.org/0000-0003-1185-1962
ORCID for Robert Nicholls: ORCID iD orcid.org/0000-0002-9715-1109

Catalogue record

Date deposited: 22 Apr 2016 09:30
Last modified: 12 Jan 2019 05:01

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