Credit: Michael Wier
Beginning in January 2024, reservoir drawdown and removal of the four Lower Klamath Project dams will cause the release of impounded sediment into the Klamath River below the site of Iron Gate Dam and exposure of sediments in the reservoir footprints. Peak concentrations of sediment – mostly dead algae, clay and fine material the consistency of talcum powder – will occur in the first few months following drawdown of the reservoirs. Modeling of sediment transport shows that suspended sediment will tend to spike in January/February 2024, with a second spike in June/July of that year, tapering off afterwards. What does that mean for downriver communities, for fish, and for the entire Klamath River ecosystem?
The good news is that the composition of the sediment has been extensively tested, and the results are reassuring. The US Environmental Protection Agency noted that, “…reservoir sediments contained generally low levels of chemical contaminants, were not acutely toxic, and were relatively homogenous. As such, it was determined at the time that the unavoidable release of sediments upon removal of the dams would not result in unacceptable adverse impacts in relation to any of the several exposure pathways evaluated.” Years of testing since early work in 2020 did not reveal any substantive new information. In short, the sediment is not a concern for human health.
However, the river will be very muddy for the first several months after dam removal, and more cloudy than usual for up to two years after the construction crews demobilize. The high turbidity and sharp reduction in dissolved oxygen will have a short-term negative impact on aquatic life as a plume of sediment moves downriver before it washes out to the ocean and dissipates.
But regulatory agencies agree that the short-term pain will lead to very long-term gains for both the ecosystem and people. The impacts to Coho salmon and other fish will be minimized by timing reservoir drawdown to avoid major fish runs (while fish are safe at sea or in tributary habitats), and there will also be a Coho collection and relocation effort. Sediment transport modeling shows that suspended sediment will tend to return to baseline conditions by 2026 with successful establishment of vegetation in the reservoir footprint areas. So, while people who live along the Klamath River will see short-term river impacts that will affect fishing and recreation opportunities, the long-term results of dam removal are expected to very positive for water quality and for healthier, more robust fish runs.