The morphological, sedimentary and hydraulic properties of two coarse clastic (pebble) beaches along the heritage coast of Glamorgan, Wales

  • N. E. Caldwell

    Student thesis: Doctoral Thesis


    This thesis attempts to clarify those morphological, sedimentary and hydraulic properties which typify coarse clastic beaches.

    A tracer study on a low energy beach at Gileston identified shape and size sorting processes. Results showed that particle thickness (C-axis) was the most susceptible parameter to swash/backwash processes, and that tracers possessing relatively larger C-axes travelled relatively further along and down-beach from the injection point. An analysis of the relationship between tracers and the background beach population showed dissimilarity between (1) 'returned tracer populations' and the original population of tracers, and (2) individual tracers on the beach surface, and material with which they were in contact (their 'host populations'). A modified model of sediment deposition beneath sea waves has been proposed.

    A number of refinements, which have successfully classified pebble beach morphology, have been made to a model originally devised for a micro tidal sand beach environment. As a result, the crucial importance of swash berm development and its location, to the identification of different depositions; environments, and hence sedimentary structures, has been recognised.

    A sedimentological study comprising granulometric data from 37,080 beach particles confirmed the existence of a basic zonational shape structure on both Gileston beach, and a high energy beach at Nash. Statistical evidence and size/shape distributions were used to quantify along and down beach sediment structure on each beach. However, an original model's preference for use of the B-axis in size/shape analysis seems to have led to an incorrect rejection of particle mass (size) as a factor determining the transportational and depositional potential of a. particle. In this thesis the identification of several pertinent sub-facies arrangements specific to each beach, has led to the conclusion that the influence of particle size on sorting is predominant when energy conditions are high, whereas shape factors predominate when energy conditions are low.

    Two new proto-type swash force transducers, each based on different physical principles, were built and field tested to provide direct swash zone wave data. Considerable developmental problems were incurred, but although swash velocity and flow pressure data were only consistent enough for a qualitative appraisal of results, the basis for a more thorough-going investigation of swash zone phase relations and entrainment pressures has been established. Future research objectives in this field have been identified.
    Date of AwardApr 1983
    Original languageEnglish
    Awarding Institution
    • Polytechnic of Wales

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