Modifying dam operating rules to deliver environmental flows: experiences from southern Africa

Abstract

Provision for environmental flows (EFs) in water use and water-resource developments has been legislated in several southern and eastern African countries. While much of the focus has been on the assessment of EFs for new water-resource developments, some attention has been paid to the possibilities of modifying the operation of existing infrastructure to deliver EFs. This paper summarizes research done to support the re-operation of the Katse Dam in Lesotho, the Clanwilliam and Kogelberg Dams in South Africa, the Cahora Bassa Dam in Mozambique and the Nyumba ya Munga Dam in Tanzania in ways that would reduce their downstream impacts. For each, the original and suggested new operating rules are presented, and the reasons for the suggested changes are summarized. The negotiation and decision-making processes relevant to each dam are also discussed, and some of the challenges faced at two of the dams (Katse and Kogelberg), where revised operating rules have been implemented, are reviewed.

Keywords:

• Environmental flows
• dams
• operating rules
• sustainable development

Notes

The Clanwilliam yellowfish spawn downstream of the dam in the summer in response to small increases in discharge, but will not spawn at temperatures below 18°C (Cambray et al. 1997; King et al. 1998).