Coastal sediment processes in Poole and Christchurch Bays and the effects of coast protection works.

Abstract

The research detailed in this thesis illustrates to the coast protection engineer some of the effects of various solutions to coastal engineering problems. The study is based on the analysis of coastal processes and present coast protection schemes in Poole and Christchurch Bays, although the conclusions are of more general application. The data used is derived from available sources and is supplemented by fieldwork of the author. The limited remote sensing data available is utilised to increase the knowledge of the physical processes within the bays. The collection of sediment samples and the surveying of beaches and cliffs together with map analysis and aerial photograph interpretation, have been used to provide an indication of the present and past status of the coastal system. An artificial renourishment scheme conducted in Poole Bay is examined. The scheme has been successful as a coast protection measure in providing a beach to protect the backshore. However, the life of the scheme was found to vary alongshore, diminishing eastward as longshore drift increases. Depending on the duration and conditions experienced during re-nourishment, this research has shown that the beaches should be "topped-up" approximately every seven to eight years. Permeable groynes built on Solent Beach have also proved to be successful, alleviating the erosion problems within their vicinity. Analysis of the beach survey data illustrates the movement and accretion of material on both sides of the groynes. A combination of coast protection measures in central Christchurch Bay is examined. The erosion and evolution of the unprotected frontage between the protected coast-lines of Highcliffe and Barton are considered in conjunction with the general concepts of log-spiral (crenulate) shaped bay development and stability. Finally, the overall effect of coast protection works to littoral drift within the bays is appraised. The future requirements for coast protection within Poole and Christchurch Bays are discussed as are the requirements for further research.

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