Geomorphology and dynamics of the Mfolozi River floodplain, KwaZulu-Natal, South Africa

Grenfell, S.E. and Ellery, W.N. and Grenfell, M.C. (2009) Geomorphology and dynamics of the Mfolozi River floodplain, KwaZulu-Natal, South Africa. Geomorphology, 107 (3-4). pp. 226-240. ISSN 0169-555X

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Official URL: http://dx.doi.org/10.1016/j.geomorph.2008.12.011

Abstract

The geomorphology and dynamics of the Mfolozi River floodplain and estuary, located in the subtropical region of northern KwaZulu-Natal, South Africa, were considered with respect to existing models of avulsion and alluvial stratigraphy. The Mfolozi River floodplain may be divided into regions based on longitudinal slope and dominant geomorphic processes. Confinement of the Mfolozi River above the floodplain has led to the development of an alluvial fan at the floodplain head, characterized by a relatively high sedimentation rate and avulsion frequency, at a gradient of 0.10%. The lower floodplain is controlled by sea level, with an average gradient of 0.05%. Between the two lies an extremely flat region with an average gradient of 0.02%, which may be controlled by faulting of the underlying bedrock. Avulsion occurrences on the Mfolozi floodplain are linked to the two main zones of aggradation, the alluvial fan at the floodplain head, and toward the river mouth in the lower floodplain. On the alluvial fan, normal flow conditions result in scour from local steepening. During infrequent, large flood events, the channel becomes overwhelmed with sediment and stream flow, and avulses. The resulting avulsion is regional, and affects the location of the channel from the floodplain head to the river mouth. Deposits resulting from such avulsions contribute significantly to the total volume of sediment stored in the floodplain, and tend to persist for long periods after the avulsion. Contrastingly, on the lower floodplain, reaching of the avulsion threshold is not necessarily linked to large flood events, but rather to long-term aggradation on the channel that decreases the existing channels gradient while increasing its elevation above the surrounding floodplain. Resultant avulsions tend to be local and do not contribute significantly to the overall volume of floodplain alluvium.

Item Type:Article
Uncontrolled Keywords:Floodplain geomorphology; Avulsions; Avulsion deposits; Floods; alluvial fan; bedrock; estuary; fluvial geomorphology; sedimentation rate; Africa; KwaZulu-Natal; Mfolozi River; South Africa
Subjects:Y Unknown > Subjects to be assigned
Divisions:Faculty > Faculty of Science > Geography
Faculty > Faculty of Science > Environmental Science
ID Code:1467
Deposited By:INVALID USER
Deposited On:10 Sep 2009
Last Modified:06 Jan 2012 16:20
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