BuRec prepares to lower reservoir levels after second high water year
Casper – Out of the last 100 years of data, in 2011 the North Platte River system received the highest inflows in recorded history, just four years after the lowest recorded inflows in 2007.
The seven dams on the North Platte River system, which is managed by the Bureau of Reclamation (BuRec), hold 2.8 million acre-feet of water, with another 280,000 acre-feet available in Glendo Reservoir’s flood control space.
Of managing a system that large, especially after the 2010 and 2011 water years, BuRec Wyoming Area Manager John Lawson said he and his staff have to be prepared for anything that might come at them. Lawson spoke at the annual Wyoming Water Association meeting in Casper Oct. 26.
Speaking of the sheer amount of snow near Centennial on Highway 130 on May 16, Lawson said, “We’d never seen snow like that before, and especially not when we were approaching the first of June. That isn’t the time to start saying we should have let more water out of the reservoirs in March.”
As it was, BuRec started taking snowpack into account in late February.
“Usually the snowpack then doesn’t mean a whole lot, but last winter we paid attention,” said Lawson.
When spring runoff ended, 2011 beat out the other years of record inflow, 1983 and 1984, which had 1,500,000 acre-feet inflows, by 400,000 acre-feet at 1,970,000 acre-feet of inflow into Seminoe Reservoir.
“The scary thing for us was 2010, but it was great we had it, because it was a wake-up call,” said Lawson. “We probably wouldn’t have made the 2011 decisions if not for 2010, which produced 1,241,000 acre-feet of inflow, when the 30-year average is 714,000 acre-feet. We really got surprised, and as a result we started evacuating our operations in late irrigation season 2010, and taking action for this year.”
Early last summer, Lawson said that come June 1 he and his staff were scratching their heads because of a snowpack nobody had ever seen.
“There were no models available for that kind of snowpack on June 1,” he said. “The best thing we could do was take experience and history and do the best we could with a projection, and we came up with 1,969,000 acre-feet of potential water as inflow into Seminoe.”
BuRec estimated the flow they thought would come into the system for every day through Sept. 30, and then projected how they’d get rid of the water.
However, come June 1 the system had only received less than 600,000 acre-feet of that prediction.
“We were sitting on a projection that said we’d get 1,400,000 acre-feet of water coming into Seminoe in two months, while the four-month average is only 700,000 acre-feet,” said Lawson. “We started scratching our head on where we were going to put it, and how to move it down through the system.”
When the runoff started to come out, Lawson said Pathfinder Dam spilled for two-and-a-half months, from May 15 through July 31.
“The previous record was a little over a month. A lot of water was pushed out of the system,” he noted. “We were releasing just over 8,300 cubic feet per second (cfs) from Pathfinder, and that doesn’t mean much, unless you live in Casper.”
While Pathfinder was spilling at that rate, at one point over 17,000 cfs was coming into Seminoe.
“For 30 days, the entire month of June, we had over 10,000 cfs coming into Seminoe,” he commented. “If we didn’t have the dams there, and we hadn’t found the space, the first affect would have been in Casper, then all the way on downstream. Luckily we didn’t have to go much more than the 8,300 cfs through Casper.”
Lawson said that Mother Nature was kind this year.
“In 2010, with all that water, June was also one of the highest precipitation months on record. If we had had a June 2010 with a snowpack 2011, all the way down the stream we would have looked at a different situation,” he stated.
Of preparation for the 2010 inflows, Lawson said the fact that the system ended with only 700,000 acre-feet in the entire system in 2007, and that in 2008 Pathfinder Reservoir would have been a flow-through river had the drought continued, area irrigators were uncomfortable with the high releases.
“We had considerable debate in Scottsbluff over the subject, and we went ahead and released, but we were put on notice what would happen if injury came about,” said Lawson.
Of the previous high water years in 1907 and 1917, Lawson said, “When I came here 22 years ago and was given the graph, I said I wanted to get out before seeing those years again, but I missed it by a year.”
“The record lowest inflow in 100 years was in 2002, when Seminoe only received 118,000 acre-feet. This year it got 1,970,000 acre-feet, a factor of about 20. If you’re wondering what will come next year, don’t ask me,” he said.
Right now BuRec is preparing to draw the reservoirs down again before spring.
“We’ll move water starting in March again, and probably even if the snowpack is average or even a little below average, because it’s too unpredictable to have too much water in the system. If the snowpack doesn’t generate in late April, we can start adjusting and cutting it back, but if we wait and the snowpack shoots up in late April and May, we can’t stand here and say we wished we’d released more water in March,” said Lawson.
Christy Martinez is managing editor of the Wyoming Livestock Roundup and can be reached at firstname.lastname@example.org.