Sustainable Reservoir Operation: Balancing Power Generation and Downstream Environmental Maintenance - The Case of the Cahora Bassa Dam

Abstract

The Cahora Bassa dam is one of the largest hydropower plants in the Southern Africa region, under the Zambezi River Basin, in Mozambique territory. The independent and standalone operation of the Cahora Bassa reservoir determines the water fluctuation in the lower Zambezi basin. Any unregulated reservoir operation may cause adverse impacts in terms of energy production performance and downstream ecosystem sustainability. A setup of the reservoir operation rules curves can contribute to maintaining regular flows in the dry and wet seasons. The variability of the hydrological regime in the Zambezi basin is cyclical, interspersed between long wet hydrological years and short dry periods. Historical averages between inflows and outflows are nearly 2,000 m3/s, generating an annual water renewal in the Cahora Bassa reservoir. However, any discharge with flows exceeding 5,000 m3/s can significantly contribute to floods in the lower Zambezi Valley, associated with contributions from river flows downstream in the rainy season. This paper addresses the Cahora Bassa reservoir's historical operation since dam construction and its impact on downstream water demand for the environment and other relevant stakeholders.