Morphological and longshore sediment transport processes on mixed beaches

Curoy, Jerome (2012) Morphological and longshore sediment transport processes on mixed beaches. Doctoral thesis (DPhil), University of Sussex.

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Abstract

Mixed beaches, with sediment sizes ranging over three orders of magnitude, are an increasingly important coastal defence on the heavily populated coasts of SE England and N France. Yet longshore transport rates and volumes, important in understanding beach sustainability, remain understudied for such beaches.

This thesis addresses the knowledge gap via field investigations of beach profile evolution, active layer measurements and tracer pebble scattering patterns on two macrotidal mixed beaches at Cayeux-sur-Mer (France) and Birling Gap (UK), eastern English Channel.

The beach topography data at both sites enabled observation of how reactive the beach profile is to hydrodynamic conditions. Each beach, in different environmental conditions, was found to have a profile that responded extremely quickly to changing hydrodynamics as a result of the combined effects of the High Water Level (HWL) and wave height. The most significant topographical changes are associated primarily with variations in the across-shore position and height of the berm.

The research contributes new baseline data to help refine the currently limited understanding of the relationship between depth of disturbance and wave height, wave period, wave direction and the degree of mixture on mixed beaches.

Consistent patterns of pebble behaviour were identified during each tidal cycle at different locations on the beach profile. The distance travelled varied with location on the beach profile, with pebbles from the upper beach tending to travel further than pebbles placed on lower parts of the beach. Upper beach pebbles generally showed a clear displacement seaward across-shore whereas lower and middle beach pebbles were affected by shorter across-shore displacements. These displacements are explained by variations in the hydrodynamic conditions, swash flows, groundwater flow, beach slope and grain size.

Finally, wave conditions and water level directly influenced the Longshore Sediment Transport (LST) rates. From these results, applying the energy flux approach, a drift coefficient (K) of 0.04 was derived for both sites.

Item Type: Thesis (Doctoral)
Schools and Departments: School of Global Studies > Geography
Subjects: G Geography. Anthropology. Recreation > GB Physical geography > GB0400 Geomorphology. Landforms. Terrain > GB0450 Coasts
Depositing User: Library Cataloguing
Date Deposited: 04 Jul 2012 14:24
Last Modified: 04 Sep 2015 13:25
URI: http://sro.sussex.ac.uk/id/eprint/39655

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