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| Titel |
Influence of basin connectivity on sediment source, transport, and storage within the Mkabela Basin, South Africa |
| VerfasserIn |
J. R. Miller, G. Mackin, P. Lechler, M. Lord, S. Lorentz |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 17, no. 2 ; Nr. 17, no. 2 (2013-02-21), S.761-781 |
| Datensatznummer |
250017723
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| Publikation (Nr.) |
 copernicus.org/hess-17-761-2013.pdf |
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| Zusammenfassung |
The management of sediment and other non-point source (NPS) pollution has
proven difficult, and requires a sound understanding of particle movement
through the drainage system. The primary objective of this investigation was
to obtain an understanding of NPS sediment source(s), transport, and storage
within the Mkabela Basin, a representative agricultural catchment within the
KwaZulu–Natal Midlands of eastern South Africa, by combining geomorphic,
hydrologic and geochemical fingerprinting analyses.
The Mkabela Basin can be subdivided into three distinct subcatchments that
differ in their ability to transport and store sediment along the axial
valley. Headwater (upper catchment) areas are characterized by extensive
wetlands that act as significant sediment sinks. Mid-catchment areas,
characterized by higher relief and valley gradients, exhibit few wetlands,
but rather are dominated by a combination of alluvial and bedrock channels
that are conducive to sediment transport. The lower catchment exhibits a
low-gradient alluvial channel that is boarded by extensive riparian wetlands
that accumulate large quantities of sediment (and NPS pollutants).
Fingerprinting studies suggest that silt- and clay-rich layers found within
wetland and reservoir deposits of the upper and upper-mid subcatchments are
derived from the erosion of fine-grained, valley bottom soils frequently
utilized as vegetable fields. Coarser-grained deposits within these wetlands
and reservoirs result from the erosion of sandier hillslope soils
extensively utilized for sugar cane, during relatively high magnitude runoff
events that are capable of transporting sand-sized sediment off the slopes.
Thus, the source of sediment to the axial valley varies as a function of
sediment size and runoff magnitude. Sediment export from upper to lower
catchment areas was limited until the early 1990s, in part because the upper
catchment wetlands were hydrologically disconnected from lower parts of the
watershed during low to moderate flood events. The construction of a
drainage ditch through a previously unchanneled wetland altered the
hydrologic connectivity of the catchment, allowing sediment to be
transported from the headwaters to the lower basin where much of it was
deposited within riparian wetlands. The axial drainage system is now
geomorphically and hydrologically connected during events capable of
overflowing dams located throughout the study basin. The study indicates
that increased valley connectivity partly negated the positive benefits of
controlling sediment/nutrient exports from the catchment by means of upland
based, best management practices. |
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