To spill or not to spill?

That is the question on the minds of local boaters anticipating a 2016 whitewater release from McPhee Dam into the Lower Dolores River.

There have not been boatable flows released from the dam, often called a spill, since 2011.

But thanks to a wet spring and summer, plus low irrigation demand, the reservoir is much fuller than this time last year, water officials report.

Carryover – the amount of water left above the dead pool at the end of the irrigation season – is at approximately 100,000 acre-feet, up from 20,000 acre feet last September.

“I would not dust off your rafts just yet,” said Vern Harrell of the Bureau of Reclamation.

But with solid carryover and a predicted strong El Niño wet weather pattern, there is a glimmer of hope.

Water engineer Ken Curtis explained that historically when runoff from normal snowpack is combined with an average carryover of 110,000 acre feet, there is a whitewater release.

“We had 240,000 acre feet flow into McPhee this year, and we need another year just like this to have a manageable spill,” Curtis said. “Generally, we have a shot at a spill with this kind of carryover.”

There have been years with strong carryover that a spill did not happen, such as in 2006, and again in 2012.

This year, historically high rainfall in May saved the day, boosting the irrigation supply from below 50 percent to a full allocation for farmers in mere weeks.

Of course, next years rafting season on the Lower Dolores all depends on a good winter, a prospect bolstered by the El Niño phenomenon associated with wetter winters for the Southwest.

“We’re on the edge of El Niño’s impact,” Curtis warned. “It could push storms south.”

Statistically, runoff data from the Dolores River over the past 30 years shows 40 percent of the time there is enough for a spill, and 15 percent the chance is on the bubble.

Based on that probability, not accounting for projections of climate change, there “is a 50 percent shot for a spill,” Curtis said. “We’ll have a good idea in March or April.”

Because of the complexities and variables of predicting runoff from snowpack, Curtis said the most advanced notice for a rafting season on the Lower Dolores is three to four weeks, unless its a really big snow year.

American Whitewater wants six weeks advance notice, but that’s impractical, officials said, because a predicted spill can be eliminated with just a few weeks of hot, windy weather.

“We built the project to fill up, and we ensure that will happen before a release is authorized,” Harrell said.

A new flow implementation plan has been formed for when there is a release for the dam.

The plan adjusts the time of the release to aid successful spawning of the native roundtail chub, flannel mouth sucker, and bluehead sucker. The release will ramped up earlier in the spring to reduce water temperature water and delay spawning until after the whitewater season.

Fish biologists report that when the shallow river below the dam warms up in early spring it is a cue for fish to spawn too early. Then the young fry can’t survive the rush of cold water during the traditional Memorial Day whitewater release.

“We will try to provide early water for temperature suppression, and also manage the spill for sediment removal,” Harrell said.

Since 2011, the boaters, reservoir managers, and fish biologists have been cooperating on how to best manage the next spill.

Conventional wisdom used to be that releasing 800 cfs was a good rafting level, but that is outdated, rafters say. A minimum flow of 1,000 or 1,200 cfs is a more ideal to clear rocks.

Tom Klema, of Peregrine Outfitters, suggested boosting minimum flows to make Snaggletooth Rapid a safer run for rafts.

“800 cfs from the dam does not translate down to Snaggletooth,” he said. “The minimum release determines the ability to navigate that rapid safely.”

jmimiaga@the-journal.com