Spring storage Wyo reservoirs dealing with too much, not enough inflow
Casper – According to Bureau of Reclamation Wyoming Area Office Manager John Lawson, the story of the 2010 water year remains to be told in the next 30 days.
“This year is setting up to be like the last two years, where we continually get these spring storms rolling in later in the season,” says Lawson, adding that makes inflows hard to forecast, which in turn makes releases harder to time.
“2009 was a big year,” says Lawson. “We got 950,000 acre-feet of runoff in the North Platte, and we’re looking at a possible 800,000 acre-feet this year. We also had 950,000 acre-feet of inflow in 2007, so this is the third year in a row with high inflows,” explains Lawson, adding, “The first two years we had a lot of storage space available, so I was happy.”
Lawson says Seminoe Reservoir in the Upper North Platte system now sits at 150 percent of the 30-year average, while Pathfinder Reservoir is 130 percent of average. Farther down the system, Glendo Reservoir is holding 110 percent of average.
“I’m running out of storage space, and we haven’t even got the runoff yet,” says Lawson.
He says there’s a unique combination of four water conditions in 2010. The first is that it’s been raining in southeast Wyoming, so those irrigators aren’t calling for the usual amount of early-season water.
“When we run operation studies we assume we’ll release a certain amount of water, but when it rains down in that area they don’t have the demand. They don’t want the water, but I’m saying I need them to take the water,” says Lawson.
The second condition is the continuous wave of storm fronts from the West Coast that dump late-season snow and rain, while the third is timing releases according to identical snow curves from the past years that have resulted in runoff ranging from 450,000 to 750,000 acre-feet.
The fourth condition is this spring’s saturation in the Chugwater and Wheatland areas. “Other years, when we were coming out of a drought, a lot of the runoff has soaked into the ground, but I’m expecting we’ll scratch our heads and wonder why we’re seeing so much runoff now that the ground is saturated before it melts out,” says Lawson.
“I was anticipating I could move water from the upper reach for delivery, but with all this gain in the lower reach of the North Platte system, I wonder what to start doing with it,” says Lawson.
He says he’s noticed Grayrocks Reservoir has begun to release more water, causing the Laramie River to rise from 40 cubic feet per second (cfs) to 200 cfs.
With Pathfinder and Seminoe approaching capacity with projected inflows, Lawson says if he ends up without room he’ll have to send water downstream, but he can’t put it in Glendo, which is currently only 25,000 acre-feet from the flood pool.
“When our irrigators down there come on we’ll release water, but the Laramie’s already got more water than they need,” he adds. “When the reservoirs are full, like they are, we need to shove water out the other end to our irrigators, but at the other end it’s raining and it’s wet.”
“We’re all sitting and wondering how we’ll end up, and it depends on the next 30 days. We’ve got to make sure we have room to put water from the next 30 days, and make the right judgment calls, and avoid holding on too long, then having to make huge releases,” says Lawson.
“We’re guessing what’s going to come in, and what’s going to go out, and it’s a mass balance. If we’ve got more coming in than we can handle, we’ll have to adjust what we can send out the other end. It’s all about timing,” says Lawson.
“The thing that’s giving us a problem is the cold weather. Not only are we stacking up more snow, but we were anticipating snow to come off at a rate we could manage with the irrigators. Now the runoff starts late, and when it starts it comes off in a hurry,” he continues.
“We’re running the scenarios to figure out what we can expect when the water starts coming at us. We could get a lot in May, or we could get most of it stacked onto June. Those are the things we’re dealing with in the North Platte system,” says Lawson.
However, Wyoming has two very different runoff scenarios this spring. While Lawson is trying to figure out where to put all the water in the North Platte system, in the Buffalo Bill area he’s told the irrigators he will only release water when they call for it, and that they need to be conservative.
“Fortunately we carried over good water from 2009, but unless something absolutely changes in Buffalo Bill, and I don’t see snow doing it this late, we’ll end with a reservoir at the end of the year that’s far lower than we’ve seen it for quite a number of years,” says Lawson.
“I’ve told our water master Bryant Startin that it’s his as far as releases – he’s calling them to meet the irrigators’ needs,” he notes. “I told the district 2010 is not setting up to be a good year in their area, and if they don’t take precautions to preserve water, the water released this year they may wish they had next year. I put it in their hands.”
Lawson says 2009 was also low to begin with, and inflows were dropping with a warm April and May, when it started raining and never quit at the end of May and through June.
“At that point we’d filled the reservoir with runoff and we were on the phone with the emergency management coordinator in Lovell every morning as we were pushing water at 7,000 cfs,” says Lawson. “That was last year, and this year we’re sitting with nothing.”
“This office is interesting because we deal with such variables,” he comments. “We’re sweating the northwest corner of the state, and telling them to do the best they can, while in the central part of the state, where I’ve been telling them the last several years to turn off, go off early and conserve water, now it’s a situation where if they don’t take the water it’ll go on by their headgates. It changes that quickly.”
“In a matter of two to three years it can go really bad, or really good,” he continues. “The systems are so dependent upon snowpack that comes in four months, and if we happen to get hit with rain it can really upset the apple cart.”
In light of the unexpected rainfall Wyoming has received the last couple years, Lawson says a dam safety project will be underway at Glendo this fall. The project is an auxiliary spillway with the capacity to pass over 100,000 cfs, while the existing spillway can only pass 10,000 cfs.
“We’ve gone through and done the probable maximum flood studies, which are way out there statistically, but the chances are there and we need to be prepared to pass something like that,” says Lawson. “If you don’t think it can happen, look at what’s going on in Tennessee right now.”
In addition to the Glendo project, Lawson says the Pathfinder Modification is also set to begin construction this fall.
“We’ve got the green light with the State of Wyoming to make the modification to the spillway, and we’ve got the conflict with the water users resolved. We worked out an agreement with them where it won’t affect them or cause additional administration,” he explains.
Meanwhile, Lawson says he looks forward to August. “No matter what’s going to happen, it will have happened by then,” he comments.