There’s so much mountain runoff predicted this spring that Bighorn Reservoir’s Horseshoe Bend Marina, just north of Lovell, Wyo., could be left high and dry on Memorial Day weekend.
That’s the irony of reservoir water management.
Under a joint management agreement with the Army Corps of Engineers, the Bureau of Reclamation, which manages Bighorn Reservoir, has to drop the lake elevation to 3,614 feet to make room for spring snowmelt. Right now, the lake is at almost 3,612 feet and the plan is to drop it to 3,601 by the end of the month to make room for an unusually high amount of predicted snowmelt — possibly 194 percent of normal between April and July, the third highest inflow in 47 years. The other two top years were 1967 and 2011.
Unfortunately, Horseshoe Bend needs a water elevation of 3,617 feet to operate.
“It’s always nice to have water but they’re following the plan,” said Lovell resident Bob Croft, of the advocacy group Friends of Bighorn Lake. “The water has to come out. There’s no use getting uptight about it.
“The folks downstream don’t like the higher water either,” he added, referring to the fly anglers who frequent the Bighorn Reservoir’s tailwater fishery.
Water, water everywhere
The Bighorn River Basin feeds the 70-mile long reservoir that stretches across the Wyoming-Montana border south of Billings and supplies water for the popular Bighorn River trout fishery, downstream of Yellowtail Dam. The Bureau of Reclamation’s predicted runoff for the drainage is more than 1.9 million acre feet, an amount that would cover 1.9 million acres in a foot of water.
Because of that massive rush of runoff, the agency is dumping water through Yellowtail Dam at 6,500 cfs right now to make room for spring snowmelt. The flow is only about 400 cfs less than the much-larger and undammed Yellowstone River is running at right now.
The Bureau of Reclamation is forecasting that the dam releases could jump to more than 7,500 cfs by June, and if the spring sees an unusual amount of rain it could even bump up to 10,500 cfs in a worst case scenario in May.
“So if things do come in, we’ll see the river releases go up some more,” said Clayton Jordan, of the bureau’s Montana office.
Jordan said the big unknown in the forecast is how much rain may fall between now and Memorial Day. A wet spring could easily boost the reservoir level to make Horseshoe Bend useable.
The beefy snowpack in the mountains has made folks downstream nervous about flooding, since the last high water year of 2011 caused millions of dollars of damage. The Bighorn Basin watershed is sitting at 134 percent of normal, with the majority of that clinging to the Bighorn Mountains.
Jordan said the snowpack on April 1 was actually higher in the Bighorn Basin this year than in the record runoff year of 2011. But April of 2011 saw a lot more snow, and then rain fell in May 2011 in unusually heavy amounts, setting records in many Eastern Montana communities.
With so much water in the system, though, the Bighorn River fishery below Yellowtail Dam could see flows of around 3,000 cfs through the fall and winter. That would be a benefit to the trout fishery, since 2,500 is seen as a preferred minimum flow by Montana Fish Wildlife and Parks. In the past, winter releases have often dropped below that figure. More water also means more aquatic bugs for fish to eat and more room in side channels for smaller fish to hide in to avoid getting eaten, boosing fish populations.
Feast and famine
The bountiful snowpack is not unique to the Bighorn Basin. For the second consecutive month, many snow telemetry or SNOTEL sites, in Montana, Wyoming and parts of Idaho, Washington and Oregon received two to three times the normal amount of precipitation, according to the U.S Department of Agriculture’s National Water and Climate Center.
Washington, most of Idaho, Montana, Wyoming and the northern parts of Colorado and Utah are forecast to have near normal or above normal water supplies, according to the Natural Resources Conservation Service. Far below-normal stream flows are expected for southern Oregon, California, Arizona, New Mexico, southern Utah and western Nevada.
In preparation for runoff from the Missouri River Basin, the Army Corps of Engineers, which manages dams from Fort Peck Reservoir downstream, has made room for 53 million acre feet of water with spring runoff forecast at 32 million acre feet.
Fort Peck Reservoir was sitting at an elevation of 2,225.11 this week. Full pool at the lake is 2,234, or more than 8 feet above the current water level.