Impacts from Dam-induced Mini-Floods

Ryan Hoover

It is proposed that one or two of Mphanda Nkuwa’s four electricity–generating turbines would be operated intermittently to provide for peak energy demands in South Africa, Mozambique’s large neighbor. This operating practice would cause daily fluctuations in river levels downstream, ranging in magnitude from 0.5 to 2.8 meters depending on proximity to the dam. The impacts of these changes in river level would be felt for over 100 miles downstream and affect thousands of people dependent on the river for their livelihoods. The Mphanda Nkuwa Environmental Impact Assessment warns, "intermittent turbine operation will infringe the rights of people to ’clean’ water, fish, safe travel, and flood recession farmland."

Mozambique simulated these mini–floods in June 2001 by releasing water from the upstream Cahora Bassa Dam. The rising waters eroded clumps of vegetation from the riverbank throughout the duration of the four–day experiment. If Mphanda Nkuwa was built and operated in this fashion, it would put the area’s most productive agricultural land (pictured below) at risk of flooding and erosion. Subsistence farmers in the Zambezi Valley depend heavily on these riverbank gardens ("baixa land") for food security. Moreover, the daily fluctuations would further complicate life for downstream populations by making fishing and navigation more difficult.

Downstream sandbars, which provide important habitat for wildlife (including the rare African Skimmer bird) would be severely eroded by these mini–floods. Fish and numerous invertebrate species could be either directly affected by the flooding or through resulting habitat loss. Experts also fear that reeds (an important building and craft material) and some rare plant species would be jeopardized.