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WATER REQUIREMENTS IN THE ORANGE RIVER BASIN

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CURRENT REQUIREMENTS

Unlike the Vaal River basin where most of the water is used for urban and industrial purposes, most water used in the Orange River basin is for irrigation with a relatively small portion being utilised for urban and industrial purposes.  River losses through evaporation also represent a large portion of the total requirement as can be seen in the figure below.

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It is very difficult to provide accurate information on the water requirements from the Orange River since they are continually changing and some are dependant upon both the weather and average flow in the river.  In order to provide an indication of the water requirements supported from the Orange River (ie excluding those supported by Vaal river water), they have been split into four broad categories namely:

  • irrigation

  • urban and industrial (including mining)

  • environmental

  • river losses

At 1994 development levels it is estimated that the total water requirement supported from the Orange River is in the order of 3 500 million m3 per annum.  The distribution of the water requirements is provided in the figure below.

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The demands are summarised in the following table which provides an indication of how the demands are split both geographically as well as by user group.

Description of water requirement Annual requirement

(million m3/a)

   
Irrigation  
Upstream of Gariep (36 400 ha) 395
Supplied locally in Riet and Modder (7 100 ha) 70
Directly from Gariep and Vanderkloof (24 300 ha) 278
To Eastern Cape through Orange/Fish Tunnel (52 700 ha) 627
Lower Orange River in South Africa (63 790 ha) 751
Lower Orange River in Namibia (2 270 ha) 39
Total from the Orange River excluding the irrigation in the Vaal River basin upstream of the Vaal/Riet confluence.        (179 640 ha) 2 160
   
Urban/Industrial Demands  
Orange River upstream of Vanderkloof Dam 70
Eastern Cape demands through Orange/Fish Tunnel 20
Downstream of Vanderkloof Dam including Namibia 40
Total urban/industrial demands 130
   
Other Requirements/return flows  
Environmental 300
River evaporation losses (varies with flow) 960
Return flows from irrigation -50
Total other requirements 1 210
   
  Total Orange River Requirements 3500

As can be seen from the above table, irrigation is by far the largest user of Orange River water.  Most of the high value irrigation takes place along the lower Orange River downstream of Prieska and there are numerous government water schemes along this stretch of river as shown in the figure below.

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The seasonal distribution of demands is also an important factor to consider when examining the water resources of the Orange River and the associated water requirements.  The figure below provides and indication of how the various demands are distributed throughout the year.  It does not include the demands supplied from Gariep Dam or those supplied through the main canal at Vanderkloof Dam.

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As can be seen from the above figure, most of the consumptive requirements occur during the summer months from October through until March.  This is to be expected due to the large influence of irrigation on the total requirement.  It does, however, present problems with regards to hydro-power generation at the Gariep and Vanderkloof dams. ESKOM currently use the two HEP stations for peak clipping power and would ideally like to generate most of the power during the cold winter months when demands for electricity are at their highest.  The conflict between the two users is shown in the figure below.

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As a result of the recent studies into the water resources of the Orange River it has been decided to generate power in accordance with the downstream requirements during all periods when water resources are scarce.  Additional power can only be generated when the main storage reservoirs are at or near full supply level. In this manner, no water is wasted and at the same time any excess water is used productively to generate power.

 

FUTURE REQUIREMENTS

Various studies have been undertaken to assess the likely future water requirements from the Orange River including the Orange River Replanning Study (ORRS) which is the basis for this web site.  For the purpose of the study it was assumed that the irrigation demands will remain at the current levels although the urban and industrial demands will increase.  in addition, the first phase of the LHWP is now operational (January 1998) and by the year 2005 the transfer will approach 900 million m3/a.   The most recent estimates indicate that the transfer is likely to be slightly lower than this initial estimate due to environmental considerations, however, for the purpose of the  ORRS it was decided to use the original value until a new value is finalised.

The figure below provides details of the expected water requirements in the year 2005 following completion of Phase 1 of the LHWP.

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