Title: Shoreline changes and sea-level rise at Long Bay, Negril, western Jamaica
Abstract: The 300 to 700 m wide beach barrier system at Negril is backed by a wide expanse of wetland (the Great Morass) underlain by peat deposits exceeding 12 m deep in places, effectively limiting present and future development to the barrier itself. 200 locations along the barrier were leveled to establish that its highest parts are between 1.5 and 2 metres above sea-level. Aerial photographs and satellite imagery covering the period from 1971 to 2008 were used to determine historical shoreline changes at 66 shore-normal beach transects, spaced at 100 m intervals. For this period the average annual shoreline retreat for the whole of Long Bay as measured by us was about 23 cm/yr. This contrasts with average values some four times higher quoted by other sources. From 1971 to 1991 retreat averaged 0.07 m/yr for the whole bay. From 1991 to 2008, a time of accelerating hotel development, average retreat rose to 0.4 m/yr. At two hot spots near the centre of the bay historical rates between 1991 and 2008 reached as much as 1-2 m/yr. A coolspot between the hotspots showed shoreline accretion between 1971 and 2003, followed by recession. The accretionary tendency is attributed to the breakwater effect of the sheltering shallow reef opposite this point. The degree of beach nourishment for the bay is unknown and has been ignored. For projections of possible shoreline changes into the future two approaches were examined. The first ignored possible effects of accelerated sea-level rise (SLR) and used a simple extrapolation of historical rates of loss into the future. This yielded a cumulative average shoreline retreat for the whole bay (base date 2008) 1.5 to 3 m by 2015, 5 to 9 m by 2030, 10 to 17 m by 2050, and as much as 25 m by 2050 for the hot The second included SLR effects, based on published projections by the IPCC and others, and employed a direct empirical correlation of loss rates with the historical and projected rates of SLR. This increased projected retreat to as much as 12 to 21 m by 2050 and up to 30 to 55 m for the hot spots. For comparison the Bruun Rule was used to estimate future shoreline recession with future SLR at 11 surveyed shore-normal profiles along the bay. These indicate averaged values for the whole bay of 7 to 12 m by 2050. We suggest the adoption of simple semi-quantitative evaluations of coastline changes, such as a Coastal Vulnerability Index (CVI) and an Estimated Hazard Area (EHA), concepts developed in the United States for its coastlines, for coastal planning and management purposes at Negril and elsewhere.
Publication Year: 2012
Publication Date: 2012-01-01
Language: en
Type: article
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Cited By Count: 11
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