In the fall of 2017, workers navigated sloppy mudflats in the bottom of the drained Paonia Reservoir in an urgent effort to prevent catastrophe: a damaged bulkhead threatened to break apart and damage the Paonia Dam's outlet works, which would have made it impossible to control releases from the reservoir. This would have made the reservoir useless for delivering irrigation water and for flood control.
A temporary fix for the bulkhead problem was completed within budget and ahead of schedule, but reservoir managers still face longer-term challenges with managing sediment and keeping the reservoir functioning to sustain North Fork Valley agriculture over the long term. Related challenges are shared by many other water managers in western Colorado as they try to maintain aging infrastructure and respond to changing social values related to water management.
The completion of the Paonia Dam in 1962 enabled the continued growth of agriculture in the North Fork Valley. A beneficial micro-climate makes the valley well-suited for high-value fruit orchards -- as long as there is sufficient water. Prior to the construction of the dam, many crops failed due to demand outstripping the supply of irrigation water in late summer. The dam currently provides water to irrigate approximately 15,300 acres of land.
When the dam was constructed, on the aptly-named Muddy Creek, it had a fifty-year "sediment design life." The designers expected the reservoir to fill with mud and become inoperable before now. Current constraints on what to do next weren't anticipated, however. We are no longer in an era where new reservoirs can easily be constructed to replace old ones. Even fixing up old ones is complicated by legal constraints that didn't exist in 1962, such as the need to ensure that the work does not have significant negative impacts on environmental, recreational or cultural resources.
The question of what to do next, within current constraints, can't be avoided much longer. The mud has come close to overwhelming the intake structure that controls releases to the stream below the dam, and has reduced the reservoir's active storage capacity from 18,150 acre-feet to about 15,000 acre-feet.
The total volume of mud is staggering: the creek has been depositing an average of over 100 acre-feet/ year of sediment to the reservoir since its construction in 1962. That's about one football field buried 100 feet deep accumulating every year -- a lot more than a whole convoy of dump trucks could haul off and sell as topsoil.
In recent years, the dam has been operated to pass a higher amount of sediment downstream, but the net inflow is still higher than the outflow. Finding a way to turn that around will require design changes to the dam outlet works and operations and careful assessment of potential impacts downstream of different release scenarios.
While streams below dams have often been described as "sediment starved," with long-term, negative impacts to channel structure and aquatic habitat, too much sediment at once or at the wrong time can negatively impact the bugs at the bottom of the food chain and ruin fish spawning habitat.
These are tricky challenges, which Bureau of Reclamation staff are wrestling with now. And whatever fix is found is unlikely to be cheap. Doing nothing is not really an option, however, either for the agricultural life of the North Fork Valley or, in the long term, for the environmental health of the stream.
The same can be said for many of our aging dams, diversion structures and canals across western Colorado. Some of these are decades older than Paonia Dam. Examples include ailing dams on the Grand Mesa, leaking ditches, and inadequate control structures.
Numerous projects to address these problems are included in the basin implementation plans developed by basin roundtables of water managers and stakeholders in 2015 as part of a statewide water planning process. However, funding to implement such projects in the future has come into question as state severance taxes on oil and gas development, which have long provided funding for water projects in Colorado, have diminished substantially.
As this year's dry winter underscores how tenuous our water supplies can be, it is worth the effort to carefully assess all the water infrastructure we rely on and determine how we can maintain it and improve it to optimize the benefits from every inch of snowpack we get.
Hannah Holm coordinates the Hutchins Water Center at Colorado Mesa University, which promotes research, education and dialogue to address the water issues facing the Upper Colorado River Basin. Support for Hutchins Water Center articles on water issues is supported by a grant from the Walton Family Foundation. You can learn more about the center at http://www.coloradomesa.edu/water-center.