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Depth of Closure and Shoreline Indicators: Empirical Formulae for Beach Management

M. R. Phillips and A. T. Williams
Journal of Coastal Research
Vol. 23, No. 2 (Mar., 2007), pp. 487-500+412-414
Stable URL: http://www.jstor.org/stable/4494217
Page Count: 17
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Depth of Closure and Shoreline Indicators: Empirical Formulae for Beach Management
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Abstract

In 1997, the effects of severe erosion along the Penarth, Wales, UK, foreshore became apparent when the beach surface fell to critical levels. A 240 m length of beach, bounded by a slipway, sea wall, and pier, was surveyed each September and April between 1997 and 2002 to assess summer and winter changes. Results in September 1997 showed that sediment transport was southerly in direction, whilst by September 2002, there had been a consistent return to the traditionally accepted south-to-north longshore drift, verified by significant differences in longshore gradients (t = 2.664; degrees of freedom [DF] = 6; p < 0.05). Analysis of changes in beach morphology has shown that erosion induced a southerly movement of beach contours, and a northerly movement was produced by accretion. Foreshore analysis has resulted in important regression models representing the variation of the shoreline indicator mean high water (MHW) with both shoreline position (mean beach level) and gain/loss of beach material. The crossshore position of the depth of closure (DoC) was 50 m seaward of the survey line, at a water depth of 5.5 m. Results from analyses of cross-shore profiles verified temporal variations in back beach level with little variation beyond the DoC. Furthermore, there was significant correlation between the two shoreline indicators, MHW and DoC (84%). This correlation, combined with a derived equation for a management response parameter (MRP = 17.035 + $tan^{-1} (x_{14}-x_6)/240[^o]$), produced simple tools to rapidly assess beach health. Results were compared with past data for interpretation of significance, and management strategies based on tabulated MRP values are suggested. A general form of this equation has been developed for testing at other beach locations, which should have significance for worldwide beach management.

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