Application of an equilibrium coastline position prediction technique
Dollard, Brendan (1998) Application of an equilibrium coastline position prediction technique. Master of Engineering thesis, Dublin City University.
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Coastal erosion is of significant interest in Ireland where reliable prediction of erosion patterns would facilitate planning for development of coastal regions. In the past, uncertainty about erosion trends has led to decisions which had costly, and environmentally detrimental, effects. The modem approach is to try to accommodate erosion rather than to prevent it. One of the ways to limit the economic cost of surrendering land to the sea is to restrict developments in areas which are under threat. This approach however requires a reliable forecast of future erosion trends. Erosion is a complex process, involving interacting factors such as wind climate, wave transformation, current effects, sea level changes, etc. which contribute to sediment transport rates. Simulation models of the process are therefore very difficult to develop, and the unavailability or expense of collecting detailed input data required for such models often prohibit their use.
Empirical models are easier to apply, and in the current research one such recently developed model, the parabolic curve technique, is applied to investigate the stability of coastline position, and vulnerability to coastal erosion. It is the first application of the technique specifically to Irish sites, and considers three bays on the east coast in Co. Wexford. Use of the technique required the gathering of data on the dominant wave approach angle, and the location of bay headlands. The study has simplified the application of the technique by the use of standard spreadsheet and graphing software. Difficulties associated with locating control points are discussed. Two different methods are used to determine the dominant wave direction, one based on the current planform or shape of the bay, and the other based on wave energy calculations.
Results show that the present coastlines in two of the three bays do not follow the ‘natural’ curvature prescribed by present climatic and geographic conditions. All three bays will suffer significant further erosion before reaching a state of ‘static’ equilibrium. The technique is used to consider future evolution of the coast, by testing the effect of changes in current wind / wave climate brought about by global warming. Erosion is seen to increase, however as bays reorient themselves toward more easterly waves, the lee of headlands will become less vulnerable to erosion. The thesis concludes with remarks on the applicability of the methods, the usefulness of predictions, and makes recommendations for future investigations.
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