Avulsion and anastomosis in the panhandle region of the Okavango Fan, Botswana

Smith, Norman D.; McCarthy, T. S.; Ellery, W.N.; Merry, C. L.; Rüther, Heinz

doi:10.1016/s0169-555x(96)00051-7

Cited by 91 publications

(31 citation statements)

References 32 publications

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“…Schumm, 1963Schumm, , 1986Ackers and Charlton, 1970;Adams, 1980;Burnett and Schumm, 1983;Ouchi, 1985;Gomez and Marron, 1991;Smith et al, 1997). In the study region, however, uplift has been spatially uniform and there is little evidence of faulting or warping, thus arguing against differential increases in valley slope as a control on meandering.…”

Section: Formation Of Local Base Levelsmentioning

confidence: 90%

Geological controls on the formation of alluvial meanders and floodplain wetlands: the example of the Klip River, eastern Free State, South Africa

Tooth

McCarthy

Brandt

et al. 2002

Earth Surf Processes Landf

103

125

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Tooth, S., McCarthy, T. S., Brandt, T., Hancox, P. J., Morris, R. (2002). Geological controls on the formation of alluvial meanders and floodplain wetlands: The example of the Klip River, eastern Free State, South Africa. Earth Surface Processes and Landforms, 27 (8), 797-815.Floodplain wetlands are common features of rivers in southern Africa, but they have been little studied from a geological or geomorphological perspective. Study of the upper Klip River, eastern Free State, South Africa, indicates strong geological controls on the formation of alluvial meanders and associated floodplain wetlands. Along this river, pronounced and abrupt changes in valley width are strongly linked to lithological variations. Where weakly cemented sandstone crops out, the Klip has laterally eroded bedrock and carved valleys up to 1500 m wide. In these valleys, the river meanders (sinuosity up to similar to1.75) on moderate gradients (0.003), the river follows a much straighter course (sinuosity similar to1.10-1.34), and floodplains are restricted in width. Long-term landscape development in the Klip and numerous similar catchments depends on the interaction between fluvial processes in the sandstone and dolerite valleys. In the sandstone valleys, vertical erosion rates are controlled by erosion rates of the more resistant dolerites downstream. Hence, in the short- to medium-term (decades to tens of thousands of years), lateral erosion dominates over vertical erosion, with the river concomitantly planing sandstone in the channel floor and reworking floodplain sediments. The thickness of alluvial fill in the sandstone valleys is limited (Peer reviewe

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Section: Formation Of Local Base Levelsmentioning

confidence: 90%

Geological controls on the formation of alluvial meanders and floodplain wetlands: the example of the Klip River, eastern Free State, South Africa

Tooth

McCarthy

Brandt

et al. 2002

Earth Surf Processes Landf

103

125

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“…The upper plane bed and alternating side bars are common depositional forms in anastomosing channels (Rust & Legun, 1983;Wende & Nanson, 1998; Tooth & Nanson, 1999). The grain size of these deposits (fine to coarse sand) is also similar to that of alluvium from anastomosing rivers (McCarthy et al, 1991;Smith et al, 1997). The presence of two facies -the main and the secondary channels -obviously adds weight to this environmental interpretation (cf.…”

Section: Discussionmentioning

confidence: 99%

“…The sandur fits with its interpretation as an anabranching channel system with low-energy discharges. The moderate sinuosity of the palaeochannels corresponds with the morphology of most anastomosing rivers (see McCarthy et al, 1991;Teisseyre, 1992;Smith et al, 1997;Makaske, 1998). The estimated depth of the first-rank palaeochannels is in agreement with the observations of McCarthy et al (1991) and Smith et al (1997).…”

Section: Discussionmentioning

confidence: 99%

Unusual development of sandur sedimentary succession, an example from the Pleistocene of S Poland

Salamon¹,

Zieliński²

2010

Geologos

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An atypical lithological development of outwash deposits in the Carpathians Foreland (S Poland) shows lower and middle parts of the sedimentary succession that are characterized by sinuous palaeochannels. This channel facies consists of laterally accreted sands derived from side bars. The sedimentary environment was a proglacial system of anabranching channels, presumably of anastomosed type. The outwash channel pattern was most probably controlled by the raising base level of the fluvial system. Both proglacial and extraglacial waters were dammed by a sandur within a small upland valley. Aggradation and progradation of the glaciofluvial deposits resulted in progressive rising of the dammed lake level. The low hydraulic gradient of the outwash streams resulted in a sinuous planform as well as a lowenergy style of deposition. Afterwards, the rising lake water was drained off through a low watershed and the entire valley became filled with outwash sediments. The bedrock morphology thus became buried and a typical unconfined sandur with a braided channel network developed during the last phase of the glaciomarginal sedimentation (upper part of the sedimentary succession under study).

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“…Although channels in the Panhandle sometimes reoccupy old meander belts and therefore partly inherit meandering forms (Smith et al, 1997), most of these meanders are currently active, as shown by cutbank erosion, numerous scroll bars (Figure 6a), and possibly by meander wavelength adjustments to small-scale neotectonic movements (Smith et al, 1997).…”

Section: Factors Contributing To Channel Pattern Adjustmentsmentioning

confidence: 99%

Controls on the transition from meandering to straight channels in the wetlands of the Okavango Delta, Botswana

Tooth

McCarthy

2004

Earth Surf Processes Landf

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Tooth, S., McCarthy, T.S., (2004) Controls on the transition from meandering to straight channels in the wetlands of the Okavango Delta, Botswana. Earth Surface Processes and Landforms 29 (13), 1627-1649 RAE2008Previous studies of alluvial rivers have shown that channel patterns form a continuum controlled by interactions among factors such as gradient, discharge, sediment size, and bank strength. Data from channels in the permanent wetlands of the Okavango Delta add to these findings by focusing on pattern transitions in channels with banks formed by sedges and grasses that are rooted in peat and underlain by unconsolidated sediment. Channels are well defined, and transport fine-medium sand as bedload between the vertical, vegetation-lined banks. Water depths, velocities, grain sizes, and bankline vegetation do not vary significantly or systematically downstream, but the permeable banks allow water to leak from the channels, contributing to an overall downstream decrease in discharge and width. In addition, as the Okavango River flows from the 2?0), but further downstream in the Fan, the narrower ( 10), thalweg meandering results in scour of the unconsolidated sediment at the bank base, leading to undermining and collapse of the vegetation, and to slow meander migration. However, as channels narrow downstream (w/d <10) with discharge losses, proportionally increasing sidewall drag exerted by bankline vegetation suppresses thalweg meandering and bank scour, and channels follow stable, less sinuous courses.Peer reviewe

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Avulsion and anastomosis in the panhandle region of the Okavango Fan, Botswana

Cited by 91 publications

References 32 publications

Geological controls on the formation of alluvial meanders and floodplain wetlands: the example of the Klip River, eastern Free State, South Africa

Geological controls on the formation of alluvial meanders and floodplain wetlands: the example of the Klip River, eastern Free State, South Africa

Unusual development of sandur sedimentary succession, an example from the Pleistocene of S Poland

Controls on the transition from meandering to straight channels in the wetlands of the Okavango Delta, Botswana

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