BILLINGS - Boaters and anglers take note: This summer’s water levels in streams and reservoirs has maxed out already, about two to three weeks early, and steady declines are likely unless precipitation in May and June picks up.
The Yellowstone River is flowing at volumes two times the norm as snow melts in the high country earlier than usual. Snowpack in the river’s headwaters remains the bright spot in the state at 71 percent of average. West of the Continental Divide river flows have already peaked because of below- normal snowpack and above-normal temperatures.
Meanwhile, reservoir levels have probably peaked and could be trending downward.
“Reservoir storage is above average from carryover last year,” said Lucas Zukiewicz, a water supply specialist for the Natural Resources Conservation Service. “They kept them pretty close to the winter reservoir max. That should help to augment flows the rest of the season.”
A good example is Fort Peck Reservoir. Mountain snowpack peaked above the reservoir on March 9 at 72 percent of normal. A near-record setting inflow of water last August from a freak rainstorm helped pump Fort Peck up and now the reservoir level is sitting at an elevation of about 2,235 feet and should fall less than a foot this month. That compares to last year when the reservoir level was 2,227 near the end of May.
“Barring any unusual rain events the reservoir is close to being as high as it is going to get and will be gradually going down over the summer and fall,” said John Daggett of the Army Corps of Engineers, which manages Fort Peck Dam. “Crooked Creek on the upper end of the reservoir still appears to be OK into the fall but it all depends on how much rain we get.”
The Crooked Creek boat ramp requires a reservoir level of 2,225 feet for boaters to have enough water to reach the bottom of the ramp.
Canyon Ferry, Bighorn
Canyon Ferry Reservoir, which last year was drawn down in anticipation of high spring runoff that never materialized leaving some boat ramps dry on Memorial Day weekend, also held its reservoir level higher through the winter. The lake was sitting at an elevation of 3,787 feet, more than 4 to 7 feet above the minimum launch levels at boat ramps.
At last count, snowpack in the Missouri River drainage that feeds Canyon Ferry was sitting at 57 percent of normal, the lowest of Montana’s three major river basins. The Columbia River basin’s snowpack was 61 percent of normal.
Bighorn Reservoir’s water elevation was 3,621 feet, which is 4 feet above the minimum launch level for Horseshoe Bend Marina, a popular site with Lovell, Wyo., area boaters.
“We won’t fill either one of those, Canyon Ferry or Yellowtail, and we’re trying to maintain river flows at the requested minimum or better,” said Tim Felchle of the Bureau of Reclamation, the agency that operates the reservoirs. “Right now, it doesn’t look real bleak, but its melting out quicker than we’d like.”
At 82 percent full, Bighorn Reservoir was gaining an inflow of 2,187 cubic feet per second, but was releasing 2,455 cfs.
With the drier spring weather the U.S. Drought Monitor listed more of southwestern Montana as suffering from moderate drought and pushed its “abnormally dry” section farther east into the southeastern corner of the state.
“The Centennial Mountains, it’s very unusual to not have snow in them at this time of the year,” Felchle said of the southwestern Montana range. “We’ve probably seen Clark Canyon Reservoir peak, and it will decline through the summer. Without rain, they’ll be calling on the storage pool.”
So May and June, typically wet months for much of Montana, hold the key to what will occur this summer. Zukiewicz said the two months, on average, can account for another 7 inches of precipitation for the Yellowstone River drainage.
In his May report, Zukiewicz wrote, “This season, river systems that do not contain reservoirs for storage, such as the Gallatin and upper Yellowstone, will see low streamflows pass through ahead of schedule.”
The Climate Prediction Center’s forecast for May through July for Montana shows the southern part of the state receiving above-normal to normal precipitation. Almost all of Wyoming is predicted to receive above-normal precipitation.