Wyo reservoir levels healthy looking toward 2010Written by Christy Hemken
“It’s been fairly dramatic,” he says of the last two above-average runoff years in the North Platte, Shoshone and Wind River basins.
“If you take all the reservoirs on the main stem of the North Platte River Basin, the total cumulative storage is 2.8 million acre-feet,” he notes. “At the end of irrigation season Sept. 30, 2007 we had 700,000 acre-feet in the entire system. As of Sept. 30 this year, we ended with 1.7 million acre-feet.”
However, he cautions the numbers can turn around and go the other way just as quickly. “That’s why this business is rather interesting,” he comments. “It comes and goes so quickly, that from a management standpoint you have to always pay attention.”
In addition, he says when storage levels start to reach capacity that can be as big of a nightmare for a reservoir operator. “We’re at a comfortable spot right now, but I don’t want a huge inflow next year. Good, but not big,” he says.
In 2008 and 2009 the North Platte system has gained 956,000 acre-feet and 964,000 acre-feet, respectively, while the 30-year average is 733,000 acre-feet. During the drought, the system only gained 118,000 acre-feet in 2002, and only levels in the 200,000’s the following years.
“We got the quick recovery because of snowpack, and the rain did have a bearing this year. We forecast as late as June 1 that we’d only get 770,000 acre-feet for 2009, because May was actually pretty dry, but then we ended up with 964,000 acre-feet of water. We missed it by almost 200,000 acre-feet,” he explains.
“When you have some reservoir space, that doesn’t give you too many sleepless nights, but now we’re getting higher reservoirs, and if we have something like that occur next year – a late spring surprise – that makes it more difficult for us to outguess Mother Nature,” he says, adding his agency will be watching very closely.
Currently Seminoe Reservoir sits at 111 percent of average, while Pathfinder is holding 146 percent of average for this time of year.
“If we get another 960,000 acre-feet of inflow next year we’ll definitely have to release water because we won’t have the space,” says Lawson of the reservoirs, which each hold a little over a million acre-feet. “If we get the average of 700,000 acre-feet, and in a predictable fashion, that would be nice.”
While the North Platte system was able to contain the high inflows of last spring, Buffalo Bill Reservoir, which holds inflows coming from the high country west of Cody and in Yellowstone via the north and south forks of the Shoshone River, proved to be a tricky situation in June.
“Buffalo Bill gave us a few anxious moments in June,” says Lawson. “June 1 we forecast around 720,000 acre-feet of inflow, and we ended up with 954,000 acre-feet.”
Once again, the forecasts were based on snowpack accumulated during the winter and spring months while the June rains increased runoff dramatically. “We started thinking about holding onto some runoff the end of May because we thought we were going to get a lot less runoff than the year before, based on snowpack levels, but then it started raining, and it kept snowing and it never got dry. We kept seeing the water coming at us,” says Lawson.
Buffalo Bill, which holds 643,000 acre-feet, had been built up to almost 600,000 acre-feet in anticipation of irrigation season. “The inflow kept coming and we had no place to go with it. We spent June working very closely with emergency management representatives, especially in the Lovell area, because we had to release water for a three-week period around 7,000 cfs, which increased to between 8,000 and 9,000 cfs down at Lovell.”
Regarding Boysen Reservoir, he says, “On June 1 we forecast an inflow of 480,000 acre-feet and we ended up with 803,000 acre-feet. It just started turning around that first week of June and it never stopped. I kept asking when it was going to quit.”
Because of the dramatic increase in inflows he says the agency released water from Boysen well into the summer at a rate of 6,500 cubic feet per second (cfs), while irrigation demands only use 1,300 cfs.
“When we were in the 2002 era the reservoir got down to 239,000 acre-feet, which was within 10 or 15,000 acre-feet of not being able to generate power,” says Lawson. “Today, at the end of irrigation season, we have 660,000 acre-feet in the reservoir.”
Boysen Reservoir is considered full at 740,000 acre-feet. “We’re at 110 percent of average,” says Lawson.
Concerning next spring’s forecast, Lawson says the agency becomes its own forecasters, drafting plans for above, below and average scenarios. “At this time of year all we can use is statistical information. I’ve been here for 20 years or so, and I’ve seen what happens when we have certain kinds of years. My observation is we might get a pretty good winter this year.”
“It’s a different year every year,” notes Lawson. “We just have to sit and think about every contingency we might have to deal with. We just got done and we’re already thinking about what we’ll deal with next March.”