Ouray Hyrdopower Reservoir Flushing Update #1

     Due to public interest in the impact of the reservoir’s sediment flushing on the Uncompahgre River, former UWP Coordinator Agnieszka Przeszlowska and the Ouray Public Health Director collected river water samples in the week following the flushing. The samples are being analyzed for heavy metal content at labs to understand some of the impacts on water quality. We hope to be able to report on those results in the coming weeks.

     The only study that UWP has received about the impact of the hydropower dam flushing on the Uncompahgre River did not address the impacts on fish and fish breeding along the river and around the reservoir. This 2001 study, conducted by the Colorado Department of Public Health, only measured the sediments and water chemistry without following up with analysis of the impact on aquatic life. Here is a related statement in a summary from the 2012 Uncompahgre Water Quality Report by John Woodling:

“All metal concentrations measured before and after the flushing operation, both  upstream and downstream of the dam, exceeded Colorado chronic stream standards  (Table 6). The copper, zinc and iron concentrations would have either restricted or  eliminated most trout species upstream and downstream of the hydropower plant without any influence from the facility. … The flushing process did not increase or decrease the amount of metals transported through the Uncompahgre River on an annual basis. However, the flushing operations resulted in the highest instantaneous metal concentrations measured in the mainstem Uncompahgre River downstream of the Hydro dam for the period of record. … Reservoir flushing operations could potentially represent an acute environmental threat.” 

     Przeszlowska stated: The last underlined sentence is a hypothesis because it has not been fully tested: there has not been an adequate study of seasonal macro invertebrate or fish dynamics to fully understand how the acute flushing events (generally spring and sometimes fall) affect aquatic life. As a result, this topic is listed as issue of concern to be eventually addressed in the watershed.

     She later added that a preliminary comparison of 2001 data on the Uncompahgre River and the Gold King Mine spill into the Animas River suggests that the Ouray Hydropower reservoir flushing resulted in higher loading of some metals than the Gold King release at its peak.

     Research and communication with local watershed partners over the past weeks has provided more information resources about heavy metal amounts in the Uncompahgre, such as a 2007 Ridgway Reservoir Water Study by Tri-County Water Conservancy. Mike Berry of the conservancy explained that the report included a limited look at water quality in the Uncompahgre River, above and below Ridgway, as well as the water in the reservoir (Section 3 of the report). 

     “As I understand it, dissolved oxygen levels in the reservoir are fairly high on a continuous basis. This is due to in part to the fact that 100,000 to 160,000 acre-feet of water makes its way through Ridgway every year so the volume of the lake (84,602 AF) turns over almost twice a year. I am told these high levels of dissolved oxygen keep the metals in the lake in solid form and the metals that have entered the lake are not suspended but rather lying on the bottom of the lake. They won’t pose a transport problem until the dissolved oxygen goes down and the metals become soluble,” Berry stated.

     He added that the water quality as it leaves the reservoir is quite good compared to what it above the reservoir, and he is quite certain that the fisheries below the reservoir were not as healthy once upon a time as they are today.

     Another source of data related to heavy metals in the Uncompahgre is Ouray High School Science Teacher Eric Fagrelius, who has been collecting data for more than a decade. This information may also be available before long.

     Though it may take time due to our limited staff and financial resources, UWP will be following up on this issue. We believe additional study of the impacts and possible alternatives to flushing the sediments into the river may be beneficial, and look forward to future collaborations with stakeholders.

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