Maputo — Hidroelectrica de Cahora Bassa (HCB), the company that operates the Cahora Bassa dam on the Zambezi River in the western Mozambican province of Tete, intends to keep the dam's floodgates closed throughout the current rainy season, in order to increase the amount of water stored in Cahora Bassa lake.
HCB hydrologist Gustavo Jessen, cited in Thursday's issue of the Maputo daily “Noticias”, said that currently the lake contains 30 billion cubic metres of water. But ideally the lake should contain 52 billion cubic metres.
Opening the floodgates was thus out of the question, said Jessen. “The level of water in the reservoir is very low”, he stressed, “and so, in order to store water, this year once again we intend not to open the floodgates, unless something completely abnormal were to happen”.
The low level of water in the lake has restricted Cahora Bassa's generating capacity. Last week, HCB announced that total production in 2017 was 13.778 million megawatt-hours of electricity, which is only 75.7 per cent of the dam's installed capacity.
The elevation of the lake, in January 2017, was 312.22 metres above sea level, eight metres lower than normal. This was an “historically low level of water storage”, HCB said. By the beginning of this month the elevation of the lake had risen to 317.69 metres - but this is still three or four metres lower than the level HCB would regard as comfortable.
The forecast for the rest of the rainy season (January to March) in the Zambezi basin is for above normal rainfall. Jessen was hopeful that this will raise the amount of water stored behind the dam, and allow HCB to increase the amount of power it generates.
If there is a great deal of rainfall upstream, then HCB would be obliged o open some of the floodgates and increase its discharges, but Jessen did not regard this as a likely scenario.
More worrying for HCB would be the persistence of drought conditions, which would oblige the company to change its electricity generation plans in accordance with the availability of water.