To maintain safe operating conditions and optimize power generation, accumulated sediment must be released from the reservoir of the Ouray Hydrodam, upstream from the Ouray Ice Park. The Uncompahgre Watershed Partnership (UWP) led studies late March of 2017 and 2019, to assess changes to water quality and sediment dynamics during sediment releases, with funding assistance from Ouray County, Town of Ridgway, Telluride Foundation, and Colorado Division of Reclamation, Mining & Safety. The aim of the multi-year study was to gather data to help the community understand whether the sediment release, which usually happens each spring, has water quality impacts on the Uncompahgre River.
UWP completed its first report for the Ouray Hydrodam Sediment Release Study, detailing the water quality impacts of the annual release into the Uncompahgre River in November 2017. Due to the release’s increased flows and concentrations of heavy metals compared to pre-release flows in the river, the study compares metals concentrations to water quality standards for various beneficial uses of water. Additionally, the study can help determine if there are any substantial environmental or public health issues created by the release.
UWP conducted the initial Ouray Hydrodam sediment release study in March 2017, during an early snowmelt period where flows were substantially higher than typical for March. Observations from this study are specific to this year’s event and additional study should occur to improve certainty. Here are links to: the announcement about study results and the full Study Report.
UWP then coordinated with local stakeholders to design a follow-up study. The sampling for 2018 was cancelled due to low river flows that caused the sediment release to be cancelled in the spring. The 2019 sampling took place in on March 22, with results to be analyzed and presented to funders that summer and fall. The report will be released online in 2021.
As expected, the change in water color was most pronounced immediately downstream of the hydrodam and decreased as distance from the dam increased. As water and sediment moved downstream, larger sediments like gravel and sand fell from the water column.
The sediment is not something created by the dam. It is constantly traveling through the Uncompahgre River naturally.If the dam did not exist, the sediment would be released over a longer period of time as the river ebbs and flows. The dam release allows the built-up sediment from the past year to move out of it rapidly over a shorter time period, but does not affect the overall quantity of sediment moved. Conservatively, the sediment release accounts for less than one percent of the annual sediment load of the Uncompahgre River.
Based on water quality data collected before, during, and after the 2017 and 2019 sediment releases, the sediment releases change water quality for a very brief period. When compared to River Watch data collected from the Uncompahgre River in Ouray and in Ridgway at County Road 24 over the past decade, metal concentrations measured during the release were not greater than the concentrations observed during runoff for most metals.