Reservoirs across the United States are experiencing significant sediment accumulation, according to a study published in the journal Nature. The research analyzed over 57,000 reservoirs and discovered an average loss of 8% in their initial storage capacity. However, the situation is more severe in some cases, with about 40% of these water bodies having lost over 25% of their storage capacity.
Particularly affected are the river basins of the Colorado, Columbia, and Rio Grande, which are among the most impacted by sedimentation.
Abigail Eckland from Louisiana State University, New Orleans, who spearheaded the study, emphasized the critical nature of these losses in arid regions. She noted, “In the West, we have more environments that are arid to semi-arid. We build reservoirs so that we can store water during wet years, and then use that water during dry years.”
Sediment naturally flows downstream in rivers, but it settles in reservoirs as the water slows, filling space that could otherwise store water. This accumulation is especially problematic during persistent droughts, when Western reservoirs are already at lower levels and have limited chances for replenishment.
Wildfires exacerbate the issue by destroying vegetation that stabilizes soil, increasing erosion risk. Burned landscapes are prone to water repellency, causing rain to run off quickly, potentially resulting in flash floods and mudslides. Storms in these areas can carry more soil into rivers, increasing sediment in reservoirs.
Eckland stated, “Increased wildfire over time can certainly increase sediment yields in a basin, and that would lead to higher reservoir sedimentation rates.” The study’s projections are based on past sedimentation rates, not directly accounting for climate change impacts. However, changes in wildfire activity and extreme precipitation could influence these rates.
To combat sedimentation, reservoir managers can employ methods like dredging or flushing sediment through dams. Diverting sediment around reservoirs is another option. The effectiveness of each approach varies based on specific factors such as dam and river characteristics and downstream effects.
This article was created by the Mountain West News Bureau, a collaborative effort among various public radio stations and NPR, supported by the Corporation for Public Broadcasting and Eric and Wendy Schmidt.
