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Title: Tracer-derived measurements of coarse clastic sediment behaviour, in the littoral zone
Author: Lee, Mark W. E.
ISNI:       0000 0001 3607 2477
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 2001
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Three aspects of coarse sediment movement of importance in coastal protection are: differential transport; vertical mixing and the rate of longshore transport. Within the present contribution state of the art tracer methods are used to improve understanding in these key subject areas. The analyses conducted show that longshore travel distance is intermittently related to particle size and position (cross-shore and vertical) on a beach. Particle size and shape are intermittently related to cross-shore transport, and size, shape and position (cross-shore) are related to vertical movement. The strongest evidence, to date is presented for the existence of secondary sorting. No clear evidence is found that factors are preferentially correlated with cumulative distance travelled relative to distance travelled per tide. The first measurements of sediment mixing depth on an engineered beach show that the thickness of the moving sediment is related to significant wave height, as is the case for open beaches. The relationship identified actually agrees very closely with that for the adjacent open beach, and with that for an open beach at another site (Charmouth, UK) which has a broadly similar grain size. Analysis of longshore transport rate data, indicates that drift efficiency (K) does not increase in value with increasing wave energy. The K values presented are, however, the highest found to date. The use of high quality wave and tracer data and/or inadequate tracer mixing are identified as possible causes of the unusual results. The first quantitative investigation of the degree of tracer incorporation confirms that mixing with the indigenous material was not complete and hence is a source of error. Longshore transport rate measurements are compared for open and engineered sections of the same beach. Drift efficiency is found to be higher on the open beach (K=0.853) than the engineered beach (K=0.534). A review of tracer theory is undertaken. Literature on the subject is found to be limited and heavily reliant on models, nevertheless, it casts doubt on the validity of the methods used in all tracer based determination of longshore (shingle) transport to date - a fact not recognised or discussed by previous authors.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available