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Sedimentary processes and deposits associated with a coastal headland: Portland Bill, southern UK

Sedimentary processes and deposits associated with a coastal headland: Portland Bill, southern UK
Sedimentary processes and deposits associated with a coastal headland: Portland Bill, southern UK

The present study investigates the sedimentary processes and deposits, associated with a coastal headland. The case study considered here is the continental shelf around Portland Bill (southern UK). A range of different scientific approaches was undertaken, in order to develop and expand upon the scientific understanding of such processes and deposits: (a) numerical modelling (including tidally-induced flow, sand transport and wave refraction); (b) in situ hydrodynamic measurements; and (c) geophysical surveys (side-scan sonar and using an high-resolution seismic profiler) and sediment sampling.

The presence of a sequence of sedimentary deposits, associated with a complex suite of bedforms and sedimentary facies, was observed. This sequence of deposits, described as headland-shelf deposits (HSD), have a reasonably symmetrical sigmoidal plan-view distribution, on both sites of the headland; they are described, sequentially, towards the headland, as: sand shoals, or "sand streams" (the Adamant and West Shoals); sandy/gravel flats, representing sand bypass zones (the East and West Flats); and sandbanks, associated with zones of sand convergence (Shambles and Portland Banks). The HSD are isolated laterally, but are connected longitudinally. Both shoals and banks have an asymmetric cross-section steeper towards the coast, being the main depocentres over the area.

The distribution of such facies and deposits is controlled by instantaneous gradients in bed shear stress and sediment transport rates; these are related to the transient development of headland-eddies and the associated bedload transport. Sediment transport, associated with a coastal headland, is defined by the occurrence of two conceptually-distinct zones: (a) an inner zone, showing sand transport towards the headland, following an increase in gradient in the sand transport rates; and (b) an outer zone, showing sand transport away from the headland, following a decrease in gradient in the transport rates. The boundary between these two zones defines a bedload convergence zone. At the tip of the headland, a scour zone (or zone of maximum erosion) is present.

University of Southampton
Bastos, Alex C
663a83a1-b9aa-46de-b876-909b5376bd25
Bastos, Alex C
663a83a1-b9aa-46de-b876-909b5376bd25

Bastos, Alex C (2002) Sedimentary processes and deposits associated with a coastal headland: Portland Bill, southern UK. University of Southampton, Doctoral Thesis.

Record type: Thesis (Doctoral)

Abstract

The present study investigates the sedimentary processes and deposits, associated with a coastal headland. The case study considered here is the continental shelf around Portland Bill (southern UK). A range of different scientific approaches was undertaken, in order to develop and expand upon the scientific understanding of such processes and deposits: (a) numerical modelling (including tidally-induced flow, sand transport and wave refraction); (b) in situ hydrodynamic measurements; and (c) geophysical surveys (side-scan sonar and using an high-resolution seismic profiler) and sediment sampling.

The presence of a sequence of sedimentary deposits, associated with a complex suite of bedforms and sedimentary facies, was observed. This sequence of deposits, described as headland-shelf deposits (HSD), have a reasonably symmetrical sigmoidal plan-view distribution, on both sites of the headland; they are described, sequentially, towards the headland, as: sand shoals, or "sand streams" (the Adamant and West Shoals); sandy/gravel flats, representing sand bypass zones (the East and West Flats); and sandbanks, associated with zones of sand convergence (Shambles and Portland Banks). The HSD are isolated laterally, but are connected longitudinally. Both shoals and banks have an asymmetric cross-section steeper towards the coast, being the main depocentres over the area.

The distribution of such facies and deposits is controlled by instantaneous gradients in bed shear stress and sediment transport rates; these are related to the transient development of headland-eddies and the associated bedload transport. Sediment transport, associated with a coastal headland, is defined by the occurrence of two conceptually-distinct zones: (a) an inner zone, showing sand transport towards the headland, following an increase in gradient in the sand transport rates; and (b) an outer zone, showing sand transport away from the headland, following a decrease in gradient in the transport rates. The boundary between these two zones defines a bedload convergence zone. At the tip of the headland, a scour zone (or zone of maximum erosion) is present.

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Published date: 2002

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Local EPrints ID: 464848
URI: http://eprints.soton.ac.uk/id/eprint/464848
PURE UUID: 5201c7b6-1145-416f-be81-abca020ea11c

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Date deposited: 05 Jul 2022 00:05
Last modified: 05 Jul 2022 03:20

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Author: Alex C Bastos

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