Sustainable Management of Dam Drawdown Operations

The assessment and mitigation of the impacts of dams on river ecosystems is one of the main research lines of the Centre for the Study of Alpine Rivers – ALPSTREAM. ALPSTREAM researchers have been studying for years the effects of excessive fine sediment accumulation on the biological components of alpine watercourses. In this context, a specific biomonitoring index has been developed, offering interesting and useful applications to effectively monitor the effects of drawdown operations and the consequent release of fine sediment in the downstream reach, with the aim of promoting the sustainable management of dams. The ALPSTREAM group has recently participated in monitoring campaigns on alpine watercourses (specifically the Varaita stream, the Po River, and the Orco stream), analyzing the communities of primary producers and benthic macroinvertebrates from various perspectives. Regarding the drawdown operations of the Sampeyre Dam (Varaita stream), a comparison with an upstream unaffected stretch shows how benthic chlorophyll a, and in particular diatoms, is negatively influenced by fine sediment deposition originating from drawdown operations. There is also a noticeable loss in diatom biodiversity, with species in the downstream stretch being more generalist and functionally less diversified.

Concerning macroinvertebrates, the drawdown operations of the dam led to a significant reduction in individual density in the downstream stretch, which will likely have detrimental effects on higher trophic levels (e.g., fish fauna) and a decrease in taxonomic richness with the loss of more sensitive taxa.