Environmental Flows

The aquatic environment should always be considered as a legitimate consumer of water, whose requirements must be met alongside basic human requirements, and ahead of any other demand. In the case of water projects involving impoundment, this translates to maintenance of flow in the reaches of the river downstream of the impounding structure, dam, or diversion. Environmental flows are required to:

• Maintain the riverine ecology
• Recharge riverine aquifers
• Maintain the river channel

Environmental Flow Requirements (EFR) are accounted for in the legislation of all of the basin states.

• Botswana - the Botswana Water Master Plan (1991) makes allowance for environmental requirements. No environmental flow studies have been carried out in the sub-basins in Limpopo River basin.
• Mozambique - The Water Law (1991) and the Water Policy (2007) give priority to environmental requirements over all other uses, except domestic use.
• South Africa - The National Water Act (1998) holds at its core two principles - Basic Human Needs and the Ecological Reserve.
• Zimbabwe - The Water Act (1998) and Environmental Management Act (2006) make allowances for primary and environmental uses - particularly in terms of aquatic ecosystems.

Source: LBPTC 2010

The map below shows a preliminary assessment of ecological status of the sub-basins of the Limpopo River basin. The classes are Environmental Management Classes (EMC) - ranging from A (close to natural conditions) to D (highly modified).

As can be seen from this map, most of the northern sub-basins (including the Changane in Mozambique) of the Limpopo River basin are classified as A to B (close to natural, relatively un-impacted status). However, with the exception of the Sand, Shingwedze and Letaba, most of the South African sub-basins are moderately to severely impacted.

Specific areas for concern are the Upper Olifants, Lephalala and Nzhelele sub-basins in terms of negative status. One area of specific concern is the Waterberg, which is located in the Lephalala sub-basin. This sub-basin is already under stress in terms of ecological flow requirements and plans for development in this area include a coal-fired power station and a coal mine.

This environmental status is elaborated in the table below, with the Environmental Management Classes defined as above and estimated Environmental Flow Requirements (EFR) calculated as a percentage of mean annual runoff (MAR). The comments column of the table provides specific reference to issues that may or do affect the EFR.

Estimates of Environmental Flow Requirements for the sub-basins of the Limpopo River basin.

Source: LBPTC 2010

For a detailed discussion of environmental flow requirements in the Limpopo River basin and the relevant legislation see Environmental Flows in Resource Management.

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