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ENVIRONMENTAL ISSUES

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From an environmental viewpoint, the Orange River is very important as it provides a belt of green vegetation through an otherwise hot and dry desert.  It also provides water to the Orange River mouth which is used by many rare and endangered birds as they migrate from one hemisphere to another annually. 

The Orange river estuary was accepted as an area of environmental importance by the RAMSAR committee on the 28th June 1991 in which they agree to preserve and protect the environmental integrity of the area.   South Africa became a signatory to the Convention on Wetlands of International Importance at Ramsar in Iran in 1971.   In terms of this agreement, South Africa must endevour to identify and protect areas which are of environmental importance with respect to wetlands used by waterfowl.

In general terms, the Orange River Mouth Wetland can be described as a delta type river mouth with a braided channel system during low flow months.  The site comprises sand banks or channel bars covered with pioneer vegetation, a tidal basin, a narrow floodplain, pans, the river mouth and a salt marsh on the south bank of the river mouth.  The annual average rainfall is less than 50mm while the potential evaporation is in the order of 3 000 mm/a.  The Orange River usually flows directly into the Atlantic Ocean, however, during low flow periods, a sand bar can form across the mouth to block the river which then rises in level and spills over into the salt marsh area.   It is therefore not a true estuary and should rather be called a river mouth.

The river mouth and the surrounding pans and salt marsh provide a sizeable area of sheltered shallow water suitable for concentrations of wetland birds.  The Orange River Mouth Wetland is used by waterbirds either for breeding purposes or as a stopover on migration routes.  The wetland is considered as the 6th most important wetland in Southern Africa in terms of the overall numbers of wetland birds it supports.   The wetland bird population can be as high as 26 000 individuals from up to 57 species.  Of the 57 species recorded in the area, 14 can be considered as endangered and appear in one or both of the South African or Namibian Red Data Books of birds.

 

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The Orange River replanning Study (ORRS) included a significant environmental component in which the environmental requirements of the river were determined.  both the instream flow requirements as well as the water requirements at the river mouth were determined and subsequently included in the water resources analyses.

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From the various environmental studies and workshops, it was concluded that the instream flow requirements (IFRs) were satisfied by the various water requirements along the Orange River with the result that no additional releases are required specifically to meet the IFRs.  At the river mouth, however, the water requirements for the environment were estimated to be between approximately 85 million m3/a and 270 million m3/a.  Details of the monthly environmental demands at the river mouth are provided in the table below.

 

Month Desirable - during normal and low flow years

(million m3)

Minimum - during drought events

(million m3)

October 32 5
November 23 13
December 35 13
January 27 13
February 33 12
March 27 13
April 21 5
May 19 3
June 16 3
July 13 0
August 13 0
September 13 3
Total 272 83