#Snowpack news: “It is a bigger decline than we had expected,” — Philip Mote

Westwide SNOTEL basin-filled map March 4, 2018 via the NRCS.

From Discover Magazine (Tom Yulsman):

Thanks in large measure to warming temperatures, the average snowpack in U.S. western states has dropped by 15 to 30 percent since 1915.

The water in that lost snowpack is comparable in volume to Lake Mead. With a maximum capacity of 9.3 trillion gallons, Mead is the West’s largest manmade reservoir.

The new data on snowpack declines are among the striking results of a study led by Philip Mote, director of the Oregon Climate Change Research Institute at Oregon State University. As part of the study, Mote and his colleagues analyzed measurements from 1,766 snow-monitoring sites in the western United States going back more than a century. The researchers found that greater than 90 percent of those sites experienced declines in snowpack. Of those, 30 percent were found to be statistically significant.

“Declining trends are observed across all months, states, and climates, but are largest in spring, in the Pacific states, and in locations with mild winter climate,” Mote and his colleagues write in their paper, published on March 2 in the journal NPJ Climate and Atmospheric Science, a Nature publication.

“It is a bigger decline than we had expected,” Mote says, quoted in a release. The primary cause isn’t less snowfall, but warmer temperatures. “In many lower-elevation sites, what used to fall as snow is now rain,” Mote notes.

The West’s snowpack comprises nature’s own water storage reservoir — and a gargantuan one at that. “Mountain snowpack stores a significant quantity of water in the western U.S., accumulating during the wet season and melting during the dry summers and supplying much of the water used for irrigated agriculture, and municipal and industrial uses,” Mote and his colleagues write in their study.

Warmer temperatures bring spring-like weather earlier than in the past. As this trend continues, increasing spring rain and earlier runoff means declining water supplies running downstream from nature’s snowpack reservoir in summer and fall — just when farmers and cities have very significant water needs.

From Oregon Public Broadcasting (Courtney Flatt):

Researchers said the decline in snowpack is connected to warming temperatures. That could have a big effect on wildlife, agriculture, cities and towns. They depend on snowmelt to supply water during the dry summer and fall months…

The study found 90 percent of long-term snow monitoring sites in the West have less snow than 100 years ago. More than 30 of those sites saw significant decreases that could not have happened by chance, statistically, Mote said.

Researchers used a model that computed the amount of snow on the ground every day — using actual weather readings. They took the weather readings from 1,766 sites across the West. They ran the model over a time period of 100 years with real weather data.

They mostly keyed in on one date: April 1, historically a high-point for snowpack.

They found the biggest changes in snowpack in the spring in California, Oregon and Washington, and in places that had milder winters.

Then, they “re-ran the model without the warming trends that have been observed, and lo-and-behold, the large number of [declining snowpack] trends went away. It ended up being more balanced, 50-50,” Mote said.

They took that as another clear sign that snowpack is decreasing because of warmer temperatures, not a lack of precipitation.

One of place that’s seen the most snowpack decreases in the West is Eastern Oregon. Mote said the most recent low snow year in 2015 was a benchmark of where water problems have happened — and will continue to happen.

“The solution isn’t in infrastructure. New reservoirs could not be built fast enough to offset the loss of snow storage — and we don’t have a lot of capacity left for that kind of storage. It comes down to managing what we have in the best possible ways,” he said.

The study was published in NPJ Climate and Atmospheric Science, a Nature publication, and was funded by the National Oceanic and Atmospheric Administration’s Regional Integrated Sciences and Assessment (RISA) program, and the U.S. Environmental Protection Agency’s Office of Atmospheric Programs.

Paonia Reservoir dramatic example of widespread water infrastructure needs — Hannah Holm

Paonia Reservoir

From the Hutchins Water Center (Hannah Holm) via The Glenwood Springs Post Independent:

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 50-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.

Intake structure during construction in 1961. Photo Credit Reclamation.

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.