The Orange River Development Project Replanning Study (ORRS) was commissioned in the mid-1990s to determine a strategy for the most beneficial utilization and optimal development of the water resources in the Orange River. Existing and potential RSA developments within the Orange River basin were considered along with the possible transfer of water to other basins. All the above mentioned studies involved key input from WRP personnel.

The Lower Orange River Management Study (LORMS) investigated and reported on the availability of water with the focus on the Lower Orange (2002 to 2004). Options for improved management through the efficiency of water use and utilizing of management measures were investigated and analyzed. Both countries were involved (Namibia and South Africa).

The Orange River Integrated Water Resources Management Plan determined the status quo in the Orange River basin in terms of available information and areas where gaps in information need to be addressed. The study involved all four basin states namely Botswana, Lesotho, Namibia and South Africa. The gaps in information identified were used to develop task descriptions for Phase 2 of the study.

The Orange River Annual Operating Analysis was awarded to WRP in 2008. This project involves the real-time management of the Orange River Project to ensure the most beneficial utilization of the resource for hydro-power generation and primary water users, while maintaining the selected reliability of supply to users. WRP personnel were also responsible for these annual operating analysis from 1995 to 2002.

Key Results

• The ORSA study found that Orange River resources were significantly less than previously estimated with the result that the full Lesotho Highlands Water Project (LHWP) cannot be undertaken. This lead to a complete re-evaluation of all further phases of the LHWP.
• The Orange River Losses study produced a hydraulic model for the Orange River (ISIS) which was modified to simulate spatially and temporally varying evaporation losses and to include a variable time step facility. Evaporation losses along the 1300 km river stretch were determined to range from 575 million m³/a at 50m3/s flow rate to 989 million m³/a at an annual release of 400m³/s.
• At the time of the ORRS a surplus of 274 million m³ was available from the ORS. No single development option can fully harness the resource, various combinations of development options were identified for realising the remaining potential of about 1 735 million m³/a from the Orange River.
• The LORMS showed the current system to be in balance by 2005. A re-regulating dam at Vioolsdrift and the use of a real-time hydraulic model were proposed to reduce the high operating requirements. To increase system yield for Lower Orange the raising of Vioolsdrift Dam and utilisation of the lower level storage in Vanderkloof Dam were recommended. The importance of improving the protection of the ecology was strongly emphasized.
• Key deliverables for the annual operating analysis includes the release schedules from Gariep and Vanderkloof dams, optimize hydropower generation, imposing water restrictions, extending the system to include other important water supply systems and development of operating rules.

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