| ORANGE RIVER: Hydrology and geohydrology |
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eWISA Home | ORANGE: MAIN INDEX | ALPHABETICAL LIST OF RIVERS | |||||||||||||||||||||||||
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Map of the ORANGE River |
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| HYDROLOGY | ||||||||||||||||||||||||||
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Upper Orange area (upstream of Douglas in the Northern Cape): Nearly 70% of the total surface runoff, which would flow through the area under natural conditions, originates from Lesotho territory, and just more than 30% from within the South African portion of the area. There are no natural lakes or wetlands of note in the area, a consequence of both topography and climate.(Ref.1) Water is transferred through the Orange/Fish tunnel from the Gariep Dam to the Fish River |
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Lower Orange area (between Douglas and Alexander Bay): Ninety percent of the runoff generated in the two Orange River Water Management Areas is generated in the Upper Orange Water Management Area . The bulk of the runoff generated in the Lower Orange comes from the Fish River in Namibia (approximately 60% of the Lower Orange runoff) but this only enters the Orange River close to the river mouth.(Ref.2). | |||||||||||||||||||||||||
| GEOHYDROLOGY | ||||||||||||||||||||||||||
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Upper Orange area (upstream of Douglas in the Northern Cape): Groundwater is widely used in the area to supply small towns (approximately 35 towns) either as the sole source of supply or in combination with surface water resources. Unfortunately the development and management of groundwater is seldom done properly. Municipalities tend to restrict their search for water to municipal boundaries. The municipalities should also investigate groundwater potential outside town boundaries as a possible source. Un-scientific borehole siting often results in dry holes being drilled. Borehole siting needs to be based on proper geo-technical work to limit the drilling of unsuccessful boreholes and to improve the yield from the boreholes. Boreholes and abstraction from boreholes are seldom managed properly and therefore the failure of boreholes in the Southern Free State is a common experience. Proper management and monitoring of groundwater sources by municipalities and other users are of vital importance. (Ref.1) | |||||||||||||||||||||||||
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Lower Orange area (between Douglas and Alexander Bay): Groundwater utilisation is of major importance across wide areas in the and often constitutes the only source of water. It is mainly used for rural domestic supplies, stock watering and water supplies to towns. As a result of the low rainfall, recharge of groundwater is limited and only small quantities can be abstracted on a sustainable basis. Artificial recharge of groundwater is practised in some areas where water from small dams is transferred through pipelines into boreholes located in the area of recharge of the main production boreholes. Aquifer characteristics (borehole yields and storage of groundwater) are also typically unfavourable because of the hard geological formation underlying most of the area. Groundwater also constitutes an important source of water for rural water supplies in the Orange River, although only a small proportion of the total available water. Much of the groundwater abstracted near the river, is actually recharged from the river and could also be accounted for as surface water. Groundwater availability in the coastal region is extremely limited as a result of the lack of rainfall. Close to the sea there is a strong risk of seawater intrusion into coastal aquifers.(Ref.2). | |||||||||||||||||||||||||
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| References | ||||||||||||||||||||||||||
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Ref.1. Department of Water Affairs and
Forestry, South Africa. 2004. Internal Strategic Perspective: Upper
Orange Water Management Area. Prepared by PDNA, WRP Consulting
Engineers (Pty) Ltd, WMB and Kwezi-V3 on behalf of the Directorate:
National Water Resource Planning. DWAF Report No P WMA.
Ref.2. Department of Water Affairs and Forestry, South Africa. 2004. Internal Strategic Perspective: Lower Orange Water Management Area. Prepared by PDNA, WRP Consulting Engineers (Pty) Ltd, WMB and Kwezi-V3 on behalf of the Directorate: National Water Resource Planning. DWAF Report No P WMA 14/000/00/0304 |
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