Chemical sedimentation in the semi-arid environment of the Okavango Delta, Botswana

McCarthy, T. S.; Metcalfe, J.

doi:10.1016/0009-2541(90)90065-f

Cited by 75 publications

(34 citation statements)

References 10 publications

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“…This value is 31% below the 457,400 tonnes estimated by McCarthy and Metcalfe (1990) based on a single water sample in August 1975. Uncertainty in our results may originate mainly from the relation between discharge and concentration, which we have crudely approximated by using a mean concentration.…”

Section: Solute Concentrationsmentioning

confidence: 88%

Sediment Transport Monitoring and Short Term Modeling in the Okavango Delta, Botswana

et al. 2010

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The Okavango Delta of northern Botswana comprises large wetlands that spread over an alluvial fan of 150 km in length. Only part of the fan is covered with wetlands but the repeated shifting of the zones prone to inundation has led to a regular distribution of sediments and eventually to the formation of a smooth fan surface. We conducted repeated solute and bedload transport measurements at the inlet and within the wetlands proper to quantify sediment input and channel aggradation rates. The relationship between flow velocity and bedload transport was used to simulate channel erosion and aggradation, and a bedload transport component was built into a numerical hydrological model of the Okavango Delta. The model was used to assess the impact of a hypothetical dam in the upstream of the wetlands on channel bed elevations and the distribution of flooded areas. Our results suggest that the contribution of solute inputs to the overall sediment accumulation of the fan has been overestimated relative to bedload inputs. The numerical simulations reveal that a dam would have an impact on channel elevations only in its immediate downstream, but an impact on the distribution of flooding would be felt over the entire wetland system.

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Section: Solute Concentrationsmentioning

confidence: 88%

Sediment Transport Monitoring and Short Term Modeling in the Okavango Delta, Botswana

et al. 2010

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“…Scholz, 1968a,b;Kautz and Porada, 1976;Watts, 1980;Netterberg, 1982;Botha and Hughes, 1992;Singer et al, 1995) and secondary silica (e.g. Smale, 1973;Summerfield, 1982Summerfield, , 1983McCarthy and Metcalfe, 1990;Nash et al, 1994a,b;McCarthy and Ellery, 1995;Nash and Shaw, 1998;Shaw and Nash, 1998) are common constituents of soils and duricrusts in many parts of southern Africa.…”

Section: Composition Of the Clay Fractionmentioning

confidence: 97%

The nature of calcareous deposits along pan margins in eastern central Namibia

Mees

2002

Earth Surf Processes Landf

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In a region along the western margin of the Kalahari in eastern Namibia and western Botswana, many pan basins have mainly calcareous deposits along part of their margins. These are typically lined by low vertical scarps. In Namibia, these pans are mainly located in dry river beds. The petrographical study of these deposits demonstrates that they consist of lacustrine sediments that have to a varying extent been affected by early-diagenetic processes and by the formation of late-diagenetic features.The original composition of the deposits ranges from highly calcareous sediments, typically with ostracod, diatom and charophyte remains, to entirely non-calcareous diatomites. The deposits generally show an upward increase in total carbonate content, which is mainly a synsedimentary feature. The early-diagenetic processes that affected the deposits include the formation of orthic siliceous nodules. At a later stage, secondary calcite enrichment occurred, leaving only the silica-impregnated sections unaffected. This enrichment partly accounts for the upward increase in total carbonate content in some profiles and often resulted in the development of a highly calcareous surface horizon. Sepiolite and amorphous silica that are part of the groundmass of the deposits may also partly have formed at this stage. Late-diagenetic features include various forms of secondary calcite and silica.This study of pan basins in eastern central Namibia indicates that a lacustrine rather than purely pedogenic origin should also be considered for calcareous deposits that commonly occur along pan margins in other parts of southern Africa.

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“…There has been considerable variation in flow through the Delta on both historical (Shaw, 1984) and Quaternary (Shaw, 1988) time scales, with the present flow regime amongst the lowest on record. Although solute levels in the river water intake are low (<30 ppm), budgetary studies (McCarthy and Metcalfe, 1990) suggest that precipitation of salts leads to the accumulation of some 450 000 tons a −1 , exceeding the clastic load by up to a factor of two. Two salt precipitation gradients are apparent, one represented by the concentration of solutes downstream (Dincer et al, 1978;Summerfield, 1982), and the other by lateral absorption of salts through fringing swamps into islands (McCarthy et al, 1986).…”

Section: The Okavango Delta and Its Silcrete Exposuresmentioning

confidence: 98%

Dual mechanisms for the formation of fluvial silcretes in the distal reaches of the Okavango Delta fan, Botswana

Shaw

Nash

1998

Earth Surf. Process. Landforms

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Silcretes exposed within river-marginal or valley settings have been described in a number of studies, but few models have been suggested for the development of these 'fluvial' silcretes. An exception is that proposed by McCarthy and Ellery (Journal of Sedimentary Research, 1995, Vol. A65, pp. 77-90) to describe mechanisms of early stage near-surface silica diagenesis in the Okavango Delta, Botswana. This paper describes the characteristics and possible origins of massive surface and sub-surface silcretes at Samedupe and Boro Junction, beyond the distal margin of the Okavango Delta and further downstream than the sites described by McCarthy and Ellery. Morphological and petrological evidence from surface exposures and three sedimentary cores suggests that other modes of formation may also be applicable. A dual model of formation is proposed: surface silcretes are suggested to have developed by silica accumulation in seasonal pools remaining after the annual Okavango flood, whilst sub-surface horizons appear to have formed under conditions of varying pH associated with fluctuating groundwater levels beneath the channel floor. This model is reviewed in the context of the fluvial silcrete debate.

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Chemical sedimentation in the semi-arid environment of the Okavango Delta, Botswana

Cited by 75 publications

References 10 publications

Sediment Transport Monitoring and Short Term Modeling in the Okavango Delta, Botswana

Sediment Transport Monitoring and Short Term Modeling in the Okavango Delta, Botswana

The nature of calcareous deposits along pan margins in eastern central Namibia

Dual mechanisms for the formation of fluvial silcretes in the distal reaches of the Okavango Delta fan, Botswana

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