Glendo Reservoir’s benefits are multi-facetedWritten by Jennifer Womack
Rain gauges at Glendo in the days surrounding Memorial Day 2008 indicated eight inches of precipitation. Downstream at Guernsey the gauges caught about six inches of rain in just a few days’ time. As the rain came irrigators stopped calling for water and the 4,000 to 5,000 c.f.s. typically released from Guernsey Reservoir that time of year stopped flowing.
“Glendo,” explains Lawson of the North Platte River system, “is the only reservoir with federal authorization for flood control.” The agency keeps flood control in mind when operating the entire system, but Lawson explains, “Glendo actually has exclusive flood control space.” Of Glendo’s roughly 800,000 acre-feet of capacity, 517,000 acre-feet are for conservation storage while 280,000 acre-feet are exclusively for flood control. When water levels surpass 517,000 acre-feet, the U.S. Army Corps of Engineers directs the releases of water from the reservoir. BuRec works with the Corps until storage numbers fall below 517,000 acre-feet.
“Last year,” says Lawson of Memorial Day 2008, “we were preparing for the increased demand for irrigation and we were relocating water from Pathfinder to Glendo with the plan to have 500,000 acre-feet in Glendo my the end of May. Over the summer we draw on it and by September we’re down to 100,000 acre-feet.”
Lawson chuckles at the drive-by comments like “Glendo is the lowest I’ve ever seen it.” Of the 100,000 to 500,000 acre-feet variation, he says, “That happens every year, year in and year out.” Managers prior to Lawson dropped the reservoir’s levels to 65,000 to 70,000 acre-feet.
“The inflows coming into Glendo jumped from 3,900 c.f.s. to approximately 11,000 c.f.s in about 72 hours,” recalls Lawson of the rains that began on the Friday before Memorial Day weekend. “We spent the wee hours of the morning on Memorial Day calling emergency management people from Glendo through Scottsbluff, Neb. because we didn’t know if we were going to be able to hold enough water in Glendo without making substantial releases downstream.”
Inflows of 11,000 c.f.s., explains Lawson, amount to 22,000 acre-feet in a 24-hour period. When you consider the next reservoir down from Glendo, Guernsey Reservoir is 45,000 acre-feet, that’s a lot of water.
“We were starting to sweat, wondering if it was going to stop raining,” says Lawson. “It happened at the same time the Missouri River was flooding downstream, so the Army Corps was not really interested in releasing any more water downstream than necessary.” Lawson says given the holiday people were camped along the river. “Can you imagine the flooding that would have occurred at Torrington and Scottsbluff if Glendo Reservoir had not been there to catch those flows?” asks Lawson.
Upstream, Lawson says he was forced to drop flows out of Gray Reef into the Platte River from 2,500 to 500 c.f.s. Concerns have been expressed that the hatch from the spring spawn was harmed below Gray Reef, but Lawson says he had no choice. Flows were reduced for about two weeks, he says, noting, “I couldn’t bring the water back up until we got out of that flood control zone at Glendo.”
Lawson says it’s also easy to forget the positive impacts changes in the river’s management have had in recent years. In 1993, based on a partnership with Game and Fish and University of Wyoming studies, BuRec began the practice of flushing flows. “The fishery out there poundage-wise has increased 10-fold,” he says. “There’s a reason you need a traffic cop to navigate the float boats,” he says of the river outside of Casper toward Alcova.
Lawson says the release of 500 c.f.s. in the winter is another measure that BuRec has made with fisheries in mind. Gray Reef Reservoir, which is used to catch water out of Alcova Reservoir, allows the steady flows and the flushing flows without affecting power generation. “We build up Gray Reef and release the water from there,” says Lawson. By catching the water at Glendo, he says it can be done without a loss of Wyoming water. When irrigating season rolls around in southeast Wyoming, he says, “We’ve got the water 127 miles closer to you.”
Prior to construction of Glendo Reservoir in 1959, Lawson says, “We would be running approximately 5,000 c.f.s. every summer from Pathfinder to meet the water needs for irrigators downstream.” Today, Lawson receives calls from concerned riverside residents when flows reach 4,000 c.f.s through Casper.
Prior to Glendo, Lawson says wintertime flows only amounted to inflows from the tributaries below Alcova, and there aren’t many. By decree the irrigation season ended Sept. 30 and didn’t begin again until May 1 so flows were non-existent. The only reservoir downstream prior to Glendo was Guernsey and its 45,000 acre-feet of storage capacity.
When Glendo was built, Lawson says 335,000 acre-feet of the storage was allocated to restore Pathfinder water. It’s a scenario that he says allowed for wintertime flows. Federal law passed as part of the authorizing legislation for construction of Gray Reef Reservoir now requires a minimum flow of 330 c.f.s, but Lawson says based on Game and Fish Department recommendations, that BuRec maintains flows at 500 c.f.s. or above whenever possible.
“Now, rather than this river being dried up at Casper,” says Lawson, “we’re running flows all winter, which we weren’t doing prior to 1959.” Prior to construction of Glendo Reservoir, he says one month of winter flows would have filled Guernsey.
“It allowed us to move Pathfinder water 127 miles further downstream closer to the irrigation,” says Lawson. “When we start irrigating we deliver it from close to the irrigators rather than releasing it up here and trying to get it down the river.”
An ability to catch water at Glendo during the winter allowed for higher winter flows offering pollution abatement by improving the quality of the water available to the municipalities along the North Platte River. Without Glendo he says communities like Casper would have been held to a stricter discharge water quality to meet standards. “The solution to pollution is dilution,” he says.
Another huge benefit was power generation. “The original and best renewable energy was hydroelectric,” he says. “We didn’t have Fremont Power Plant at Pathfinder. It wasn’t feasible when we could only run water through the generators six months out of the year.” Power production at Alcova was added in the 1960s.
“We’re now using all of that winter flow for power generation,” says Lawson. “For a piecemeal system you’d think we’d planned it this way.” After bay dams, like Gray Reef near Alcova, allow BuRec to meet peak power demand while maintaining consistent flows in the Platte River.