Lack of a snowpack: Low water levels could harm multiple fisheries
It’s May 2, and water managers, irrigators and anglers are waiting anxiously for the May snowpack report from the Natural Resources Conservation Service.
So, far it hasn’t been a lot of good news when it comes to snowpack and water flow predictions for this summer.
As of April 29, the Bureau of Reclamation reported the Colorado River basin registered among the lowest overall snowpack in the state at only 72 percent of average. Most of the other major basins ranged from 61-80 percent ranges, including the Gunnison Basin at 71 percent.
The upper Rio Grande Basin topped the state list at 87 percent of average.
Although reservoir storage remains adequate across the state, the lack of a snowpack to augment water needed for early-summer irrigation may mean shortages or cutbacks later in the year.
This could affect fisheries, as low water levels mean higher water temperatures and potential loss of habitat as streams and rivers shrink.
Hydrologists from the Bureau of Reclamation said neither Taylor Park nor Blue Mesa reservoirs are expected to fill this summer.
The Bureau on its website said it’s likely Blue Mesa will top out at 7,512 feet elevation, about 4 feet short of filling.
At current snowpack levels, it’s predicted the Gunnison River through the Gorge and Black Canyon will remain in the 550-600 cubic feet per second range most of the summer.
The most recent forecast for a peak flow to meet the senior Black Canyon Water Right is a one-day peak in the range of 3,425 cfs, along with a six-day ramp up and a six-day ramp down to about 800 cfs.
If and when that peak might occur won’t be decided until after the May snowpack readings are available, said lead hydrologist Dan Crabtree of the Bureau’s Grand Junction office.
“It may be the middle of May but we can’t pin ourselves down until we get the May 1 forecast and we know what we are working with,” Crabtree said.
The outlook might not get much better, according to the April 1 snowpack report from the Natural Resources Conservation Service.
“Given the current deficit across northern Colorado, the odds of reaching a near-average snowpack remain at less than 10 percent at this time,” said Allen Green, State Conservationist with the NRCS. “Given the marginal snowpack conditions across much of the state, the outlook for spring and summer water supplies remains below average for most of Colorado.”
Bureau of Reclamation hydrologists are watching the Cimarron River and the level of Silver Jack Reservoir, changes in which affect the Cimarron’s flows into Crystal Dam, the last dam before the Gunnison River spills into the Black Canyon.
“We want to use that water as efficiently as possible, but I’m guessing (the peak flow will come) the second or third week of May,” Crabtree said.
Even with careful watching, a sudden hot spell in May can bring water down a lot quicker than expected or desired.
A sudden burst from the upper Cimarron River basin last spring pushed Silver Jack to spill and that in turn pushed the Gunnison River higher and faster than expected.
Those Cimarron flows, along with additional runoff flows from the North Fork of the Gunnison, gave water managers a little concern when peak flows at Delta neared flood stage.
Depending on their timing, high flows can affect trout fry, particularly brown trout fry which emerge from the gravel in mid-May. According to the Division of Wildife, during the drought from 2002-2006, brown trout fry benefitted from the low flows, with more surviving when flows stayed around 550 cfs.
In 2009, however, flows in the gorge peaked at close to 6,800 cfs the second week in May, just as the fry were emerging. That could mean a gap in the age-class of brown trout, something anglers might not notice this year but may see in a year or two.
DOW aquatics biologist Dan Kowalski reported earlier this winter his 2009 fish census showed a 38 percent decline in the number of brown trout more than 14 inches long.
He said this was because of lower survival of the 2007 year class and fewer trout reaching that “quality class” size because of lower growth rates.
At the January Aspinall operations meeting, Kowalski reported that studies indicate a May peak flow favors rainbows and a June peak (or none at all) favors brown trout.
He also said flows in the 2,000- 5,000 cfs range are sufficient to move fines, gravel, and cobble-sized sediment, countering one argument some anglers use for seeking much higher peak flows.