An evaluation of the spatial variability of sediment sources along the banks of the Modder River, Free State Province, South Africa
Tsokeli, Raboroko David
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The study focuses on the characteristics of the Modder River in the Free State. The Modder River plays an important role in supplying water for domestic, agricultural and industrial uses in the Bloemfontein, Botshabelo and Thaba Nchu areas. According to present (2001) estimates by the Centre of Environmental Management of the University of the Free State, the Modder River is exploited to its full capacity owing to the construction of dams. As the name of river suggests, the Modder River is said to have high sediment loads. In Afrikaans, modder means mud. The drainage pattern of the Modder River reveals well-developed dendritic drainage on the eastern part of the catchment and an endoreic drainage pattern on the western part. This study aims to evaluate the spatial variability of sediment sources along the main course of the Modder River as well as assess the possible role of fluvial geomorphology in river management. The study is based on the hypothesis that the high sediment load in the Modder River main course is caused more by riverbank processes than by the surface of the basin. Helicopter and fieldwork surveys were carried out in order to obtain the required materials (variables). The spatial variability of bank-forming material, vegetation cover, type and channel form were investigated in order to realise the aim of this study. The channel form of the Modder River indicates a decrease in sediment loads since the channel form shows some shrinkage immediately below the Krugersdrift Dam. The Modder River transports less and less sediments downstream as a result of a high number of constructed dams. Dams are barriers that create discontinuities in the channel system. Observations of the characteristics of the banks of the Modder River reveal that these banks are resistant to erosion owing to the luxuriant vegetation growth and low stream power because of the channel gradient. A question arises as to whether the Modder River really has such high sediment loads as its name suggests. Given the current state of the Modder River, high sediments are highly localised at certain sections of the stream. The transfer of sediments from one part of the river to another depends on the availability of sediment sources in space and time.
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Koning, Nadene (University of the Free State, 1998-11)English: The Modder River is a relatively small river which drains an area of 7 960 km² , in the central region of the Free State Province, South Africa and has a mean annual runoff of 184 x 10⁶ m³ . Botshabelo is a city ...
Vegetation ecology of the putative Palaeo-Kimberley and Palaeo-Modder rivers and their catchments, Free State, South Africa Van Aardt, Andri Corne (University of the Free State, 2015-06)English: The Free State is often seen as a flat and boring landscape with no prominent features in the region. However, when looking at the western Free State an intriguing landscape with numerous pans is revealed. Several ...
Unknown author (National Museum, 1975)