SEDIMENTARY PROCESSES IN THE RIVER-DOMINATED MVOTI ESTUARY, SOUTH-AFRICA

Research output: Contribution to journalArticle

40 Citations (Scopus)

Abstract

The Mvoti River enters the Indian Ocean on the Natal coast of South Africa. In its lower reaches the river comprises a narrow, shallow channel that traverses a broad floodplain. At the coast, an outlet to the sea is maintained through a sandy barrier across an underlying rock outcrop. Seawater intrusion through the outlet is prevented by the elevation of the rock outcrop and hence reversing currents and tidal salinity variations typical of estuaries are not developed in the lower reaches of the river. Sedimentary deposits and processes in the back-barrier area are predominantly fluvial and the system is best classified as a river-dominated estuary: a lack of coastal progradation prevents its definition as a delta. The greatest geomorphological impacts in the channel and barrier are caused by extreme river floods. Sedimentary processes revealed by aerial photography and field measurements in the Mvoti show changes in response to discharge variation. Within the normal range of discharge variation the channel varies in dimension and morphology but no major long-term buildup of sediment is evident in the floodplain or channel. Minor floods deposit muddy overbank deposits. During such floods, the channel gradient is increased by barrier breaching and channel shortening, but wave-dominated barrier processes act to close the breach rapidly. Superimposed on these short-term changes is a cyclic pattern driven by major floods which cause lateral channel erosion and overbank deposition. Post-flood recovery involves progressive channel confinement and stabilisation as flow reverts to a single or braided channel and the floodplain is re-vegetated. After major floods the channel assumes a position in the centre of the floodplain but subsequently it shows a tendency to migrate to the edge of the floodplain and elongate its channel. Current incorrect perceptions of the river-mouth area as an estuary degraded by siltation are based on a comparison of present morphology with typical wave-dominated estuaries, and lack of recognition of the Mvoti as one of a suite of river-dominated estuaries. The study highlights the need for a suite of universally applicable models not only for estuaries, but for transitional fluvio-marine environments in general.
LanguageEnglish
Pages271-300
JournalGeomorphology
Volume9
Issue number4
Publication statusPublished - Jun 1994

Fingerprint

estuary
river
floodplain
outcrop
Africa
flood deposit
siltation
coast
aerial photography
progradation
rock
marine environment
stabilization
seawater
erosion
salinity
sediment

Cite this

@article{0c9dc26d57904307a79dd5bae8e6200c,
title = "SEDIMENTARY PROCESSES IN THE RIVER-DOMINATED MVOTI ESTUARY, SOUTH-AFRICA",
abstract = "The Mvoti River enters the Indian Ocean on the Natal coast of South Africa. In its lower reaches the river comprises a narrow, shallow channel that traverses a broad floodplain. At the coast, an outlet to the sea is maintained through a sandy barrier across an underlying rock outcrop. Seawater intrusion through the outlet is prevented by the elevation of the rock outcrop and hence reversing currents and tidal salinity variations typical of estuaries are not developed in the lower reaches of the river. Sedimentary deposits and processes in the back-barrier area are predominantly fluvial and the system is best classified as a river-dominated estuary: a lack of coastal progradation prevents its definition as a delta. The greatest geomorphological impacts in the channel and barrier are caused by extreme river floods. Sedimentary processes revealed by aerial photography and field measurements in the Mvoti show changes in response to discharge variation. Within the normal range of discharge variation the channel varies in dimension and morphology but no major long-term buildup of sediment is evident in the floodplain or channel. Minor floods deposit muddy overbank deposits. During such floods, the channel gradient is increased by barrier breaching and channel shortening, but wave-dominated barrier processes act to close the breach rapidly. Superimposed on these short-term changes is a cyclic pattern driven by major floods which cause lateral channel erosion and overbank deposition. Post-flood recovery involves progressive channel confinement and stabilisation as flow reverts to a single or braided channel and the floodplain is re-vegetated. After major floods the channel assumes a position in the centre of the floodplain but subsequently it shows a tendency to migrate to the edge of the floodplain and elongate its channel. Current incorrect perceptions of the river-mouth area as an estuary degraded by siltation are based on a comparison of present morphology with typical wave-dominated estuaries, and lack of recognition of the Mvoti as one of a suite of river-dominated estuaries. The study highlights the need for a suite of universally applicable models not only for estuaries, but for transitional fluvio-marine environments in general.",
author = "Andrew Cooper",
year = "1994",
month = "6",
language = "English",
volume = "9",
pages = "271--300",
number = "4",

}

SEDIMENTARY PROCESSES IN THE RIVER-DOMINATED MVOTI ESTUARY, SOUTH-AFRICA. / Cooper, Andrew.

Vol. 9, No. 4, 06.1994, p. 271-300.

Research output: Contribution to journalArticle

TY - JOUR

T1 - SEDIMENTARY PROCESSES IN THE RIVER-DOMINATED MVOTI ESTUARY, SOUTH-AFRICA

AU - Cooper, Andrew

PY - 1994/6

Y1 - 1994/6

N2 - The Mvoti River enters the Indian Ocean on the Natal coast of South Africa. In its lower reaches the river comprises a narrow, shallow channel that traverses a broad floodplain. At the coast, an outlet to the sea is maintained through a sandy barrier across an underlying rock outcrop. Seawater intrusion through the outlet is prevented by the elevation of the rock outcrop and hence reversing currents and tidal salinity variations typical of estuaries are not developed in the lower reaches of the river. Sedimentary deposits and processes in the back-barrier area are predominantly fluvial and the system is best classified as a river-dominated estuary: a lack of coastal progradation prevents its definition as a delta. The greatest geomorphological impacts in the channel and barrier are caused by extreme river floods. Sedimentary processes revealed by aerial photography and field measurements in the Mvoti show changes in response to discharge variation. Within the normal range of discharge variation the channel varies in dimension and morphology but no major long-term buildup of sediment is evident in the floodplain or channel. Minor floods deposit muddy overbank deposits. During such floods, the channel gradient is increased by barrier breaching and channel shortening, but wave-dominated barrier processes act to close the breach rapidly. Superimposed on these short-term changes is a cyclic pattern driven by major floods which cause lateral channel erosion and overbank deposition. Post-flood recovery involves progressive channel confinement and stabilisation as flow reverts to a single or braided channel and the floodplain is re-vegetated. After major floods the channel assumes a position in the centre of the floodplain but subsequently it shows a tendency to migrate to the edge of the floodplain and elongate its channel. Current incorrect perceptions of the river-mouth area as an estuary degraded by siltation are based on a comparison of present morphology with typical wave-dominated estuaries, and lack of recognition of the Mvoti as one of a suite of river-dominated estuaries. The study highlights the need for a suite of universally applicable models not only for estuaries, but for transitional fluvio-marine environments in general.

AB - The Mvoti River enters the Indian Ocean on the Natal coast of South Africa. In its lower reaches the river comprises a narrow, shallow channel that traverses a broad floodplain. At the coast, an outlet to the sea is maintained through a sandy barrier across an underlying rock outcrop. Seawater intrusion through the outlet is prevented by the elevation of the rock outcrop and hence reversing currents and tidal salinity variations typical of estuaries are not developed in the lower reaches of the river. Sedimentary deposits and processes in the back-barrier area are predominantly fluvial and the system is best classified as a river-dominated estuary: a lack of coastal progradation prevents its definition as a delta. The greatest geomorphological impacts in the channel and barrier are caused by extreme river floods. Sedimentary processes revealed by aerial photography and field measurements in the Mvoti show changes in response to discharge variation. Within the normal range of discharge variation the channel varies in dimension and morphology but no major long-term buildup of sediment is evident in the floodplain or channel. Minor floods deposit muddy overbank deposits. During such floods, the channel gradient is increased by barrier breaching and channel shortening, but wave-dominated barrier processes act to close the breach rapidly. Superimposed on these short-term changes is a cyclic pattern driven by major floods which cause lateral channel erosion and overbank deposition. Post-flood recovery involves progressive channel confinement and stabilisation as flow reverts to a single or braided channel and the floodplain is re-vegetated. After major floods the channel assumes a position in the centre of the floodplain but subsequently it shows a tendency to migrate to the edge of the floodplain and elongate its channel. Current incorrect perceptions of the river-mouth area as an estuary degraded by siltation are based on a comparison of present morphology with typical wave-dominated estuaries, and lack of recognition of the Mvoti as one of a suite of river-dominated estuaries. The study highlights the need for a suite of universally applicable models not only for estuaries, but for transitional fluvio-marine environments in general.

M3 - Article

VL - 9

SP - 271

EP - 300

IS - 4

ER -