SEDIMENTATION IN THE CLIFF-BOUND, MICROTIDAL MTAMVUNA ESTUARY, SOUTH-AFRICA

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Abstract

The Mtamvuna Estuary on the Natal coast of South Africa is located in a drowned river valley and is surrounded by cliffs. It has a spring tidal prism of about 350 x 10(3) m3. Sedimentary environments in the estuary can be divided into upper and middle reaches, and barrier-associated sand bodies. The estuary exhibits limited floodplain development and small intertidal areas. The bedrock valley is presently infilled with sediment to about 90% of its capacity. This may be attributed to low sediment yields from the predominantly mud-yielding catchment lithologies. The low fluvial bedload yield to the coast is reflected in the wholly transgressive barrier sands and lack of Holocene sandy deposits on the coast and continental shelf. A significant proportion of the sediment in the estuary is derived from adjacent cliffs. Barrier morphology reflects variations in fluvial and nearshore dynamics. Enhanced flood-tidal currents and low river flow encourage flood-tidal deposition in the estuary, whereas increased river flows transport flood-tidal delta sediments seaward. Episodic overwash events deposit sand in the back-barrier area and promote barrier rollover. The volume of sediment in the barrier-associated sand bodies, however, appears to remain constant and the barrier maintains a dynamic equilibrium. Morphological responses to fluvial floods are dramatic but short-lived and are restricted mainly to the barrier which may be completely eroded during floods. Eroded sediment is deposited offshore as an ephemeral delta but when the flood wanes, wave action gradually reworks the delta sands onshore to reform the barrier which ultimately assumes its equilibrium position and morphology.
LanguageEnglish
Pages237-256
JournalMarine Geology
Volume112
Issue number1-4
Publication statusPublished - Jun 1993

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cliff
estuary
sedimentation
sand
sediment
river flow
nearshore dynamics
coast
episodic event
flood wave
ria
wave action
sediment yield
bedload
tidal current
low flow
floodplain
continental shelf
bedrock
lithology

Cite this

@article{2d68e64748e5410ca69c7157504aa499,
title = "SEDIMENTATION IN THE CLIFF-BOUND, MICROTIDAL MTAMVUNA ESTUARY, SOUTH-AFRICA",
abstract = "The Mtamvuna Estuary on the Natal coast of South Africa is located in a drowned river valley and is surrounded by cliffs. It has a spring tidal prism of about 350 x 10(3) m3. Sedimentary environments in the estuary can be divided into upper and middle reaches, and barrier-associated sand bodies. The estuary exhibits limited floodplain development and small intertidal areas. The bedrock valley is presently infilled with sediment to about 90{\%} of its capacity. This may be attributed to low sediment yields from the predominantly mud-yielding catchment lithologies. The low fluvial bedload yield to the coast is reflected in the wholly transgressive barrier sands and lack of Holocene sandy deposits on the coast and continental shelf. A significant proportion of the sediment in the estuary is derived from adjacent cliffs. Barrier morphology reflects variations in fluvial and nearshore dynamics. Enhanced flood-tidal currents and low river flow encourage flood-tidal deposition in the estuary, whereas increased river flows transport flood-tidal delta sediments seaward. Episodic overwash events deposit sand in the back-barrier area and promote barrier rollover. The volume of sediment in the barrier-associated sand bodies, however, appears to remain constant and the barrier maintains a dynamic equilibrium. Morphological responses to fluvial floods are dramatic but short-lived and are restricted mainly to the barrier which may be completely eroded during floods. Eroded sediment is deposited offshore as an ephemeral delta but when the flood wanes, wave action gradually reworks the delta sands onshore to reform the barrier which ultimately assumes its equilibrium position and morphology.",
author = "Andrew Cooper",
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SEDIMENTATION IN THE CLIFF-BOUND, MICROTIDAL MTAMVUNA ESTUARY, SOUTH-AFRICA. / Cooper, Andrew.

In: Marine Geology, Vol. 112, No. 1-4, 06.1993, p. 237-256.

Research output: Contribution to journalArticle

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N2 - The Mtamvuna Estuary on the Natal coast of South Africa is located in a drowned river valley and is surrounded by cliffs. It has a spring tidal prism of about 350 x 10(3) m3. Sedimentary environments in the estuary can be divided into upper and middle reaches, and barrier-associated sand bodies. The estuary exhibits limited floodplain development and small intertidal areas. The bedrock valley is presently infilled with sediment to about 90% of its capacity. This may be attributed to low sediment yields from the predominantly mud-yielding catchment lithologies. The low fluvial bedload yield to the coast is reflected in the wholly transgressive barrier sands and lack of Holocene sandy deposits on the coast and continental shelf. A significant proportion of the sediment in the estuary is derived from adjacent cliffs. Barrier morphology reflects variations in fluvial and nearshore dynamics. Enhanced flood-tidal currents and low river flow encourage flood-tidal deposition in the estuary, whereas increased river flows transport flood-tidal delta sediments seaward. Episodic overwash events deposit sand in the back-barrier area and promote barrier rollover. The volume of sediment in the barrier-associated sand bodies, however, appears to remain constant and the barrier maintains a dynamic equilibrium. Morphological responses to fluvial floods are dramatic but short-lived and are restricted mainly to the barrier which may be completely eroded during floods. Eroded sediment is deposited offshore as an ephemeral delta but when the flood wanes, wave action gradually reworks the delta sands onshore to reform the barrier which ultimately assumes its equilibrium position and morphology.

AB - The Mtamvuna Estuary on the Natal coast of South Africa is located in a drowned river valley and is surrounded by cliffs. It has a spring tidal prism of about 350 x 10(3) m3. Sedimentary environments in the estuary can be divided into upper and middle reaches, and barrier-associated sand bodies. The estuary exhibits limited floodplain development and small intertidal areas. The bedrock valley is presently infilled with sediment to about 90% of its capacity. This may be attributed to low sediment yields from the predominantly mud-yielding catchment lithologies. The low fluvial bedload yield to the coast is reflected in the wholly transgressive barrier sands and lack of Holocene sandy deposits on the coast and continental shelf. A significant proportion of the sediment in the estuary is derived from adjacent cliffs. Barrier morphology reflects variations in fluvial and nearshore dynamics. Enhanced flood-tidal currents and low river flow encourage flood-tidal deposition in the estuary, whereas increased river flows transport flood-tidal delta sediments seaward. Episodic overwash events deposit sand in the back-barrier area and promote barrier rollover. The volume of sediment in the barrier-associated sand bodies, however, appears to remain constant and the barrier maintains a dynamic equilibrium. Morphological responses to fluvial floods are dramatic but short-lived and are restricted mainly to the barrier which may be completely eroded during floods. Eroded sediment is deposited offshore as an ephemeral delta but when the flood wanes, wave action gradually reworks the delta sands onshore to reform the barrier which ultimately assumes its equilibrium position and morphology.

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