Above-average snowpack last winter triggered a rarely seen extended whitewater release on the Dolores River below McPhee Dam that lasted 85 days.

An estimated 24,000 boaters flocked to the 200 miles of river between March 29 and mid-June, according to the Tres Rios office of the Bureau of Land Management.

“With most boating for two to three days at a time, we estimated 56,000 visitor days,” said recreation planner Jeff Christenson. “That’s pretty impressive.”

He and boater groups, reservoir managers and ecologists gave a breakdown of the epic Dolores River season below the dam to an audience of 50 river users at the Dolores Community Center on Aug. 16.

“It was a great year for boating, with more boating days than we’ve had in a long time,” said Amber Clark, director of the Dolores River Boating Advocates. “It was good for ecological flows, and all water allocations were met.”

There were some challenging moments, though, as water managers, working closely with boaters and ecologists, grappled with how to release the massive amount of runoff for maximum boating and environmental benefits.

For weeks, releases mostly ran between 800 and 1,500 cubic feet per second, a respectable flow for most boaters and close to a natural spring hydrograph.

But for about 10 days, the river ran at a thrilling 2,000 cfs level, only to be outdone by a first-ever 4,000 cfs release for three days in mid-May.

The spike was designed to scour the river channel, which had filled in with silt after a drought from 2011 to 2015 produced no whitewater releases.

One criticism heard from boaters is that the boatable flows stopped before the Memorial Day weekend, only to start up again in June, Clark said.

It was explained that after the high flows, the reservoir level was knocked down quite a bit, and managers – erring on the side of caution – decided to close the dam and let the lake fill, then manage the remaining runoff into June.

“It was a difficult decision, but one we supported,” Clark said. “We felt that the rare spike of 4,000 flows was important for the river.”

Because of the difficulty of predicting late-season snowpack and runoff volume, June flows below the dam were up and down as inflow into the reservoir fluctuated sometimes day to day depending on the weather.

A tough challenge is figuring out a way to even out multiple spikes of late-season releases to give boaters more predictability for trips, Clark said.

“It’s a problem to tackle so the tail-end release is managed with more honed-in detail for boating,” she said.

“We understand the variables, and that it is a challenge managing this resource, given the constraints.”

Nathan Fey of American Whitewater gave preliminary results of an ongoing river survey for boaters on the lower Dolores this year.

So far, 540 boaters have filled out the survey, but organizers would like to have more participants. Boaters who floated the river below the dam are encouraged to fill out the survey, which is available on the American Whitewater website.

Most survey respondents report they are advanced or expert boaters, and 92 percent were on private trips. Most of the boaters in the survey were from Colorado, followed by Utah.

“The general response to the release was positive, and that the river is more navigable at higher water levels,” Fey said, adding that a sense of crowding is becomes a factor.

When boaters were asked whether they had to cancel or reschedule their trip because flows had stopped during their planned time frame, 30 percent said that was the case.

Advanced notice of flow conditions is important, according to survey respondents. For release schedules before Memorial Day, 50 percent of respondents said there was adequate notice.

After that holiday, only 25 percent said there was adequate notice, according to preliminary results.

More predictable flows has economic impacts for the region, Fey said, because “scheduled releases with advance notice brings in more money.”

The big water season benefited the ecological needs of the river as well, said Celine Hawkins of The Nature Conservancy, who along with others, conducted numerous studies throughout the whitewater spill.

The higher the flows, the more benefits to the river, she said.

“Flushing flows of 2,000 cfs and higher especially benefit native fish by scouring out pools, creating more room for them to hunker down and survive low-flow seasons.”

Higher flows also create an exchange of nutrients between the river channel and the higher flood plain, promoting cottonwood growth and recharging the alluvial groundwater.

“We had five weeks of peak flows, which had not happened in 10 years,” Hawkins said. “The variety of flows was really fun and really important for the ecology.”

jmimiaga@the-journal.com