Consultant says smaller, off-channel reservoirs have better chances
JEFF GEARINO Southwest Wyoming bureau | Posted: Saturday, August 27, 2005 12:00 am
PINEDALE - The Green River Basin is one of the few areas left in Wyoming that has water to develop and the land necessary to build additional dams and reservoirs.
It will take is time, money and a U.S. Army Corps of Engineers permit to make it happen.
To get that elusive permit, the state will have to convince the corps there is an overwhelming need and purpose for the additional water, a minimal loss of wetlands and an overall economic benefit for Wyoming.
That will be no mean feat, but it is possible, a water consultant told state water officials this week.
"I think there are some permittable projects up there (in the Upper Green River Basin)," said Mike Carnevale of TST Environmental Services Inc., a Denver consulting firm who is studying possible dam and reservoir sites for the state.
"If you can define the need and conduct the economic analysis necessary to determine if it's a good investment for the state and for irrigators … if you can make those persuasive arguments to try and sell the projects to the corps, then I think some of these are doable," he said. "You've got to have sufficient purpose and need to justify building these big reservoirs in the basin at this time."
As part of the hunt for possible dam sites, the Water Development Commission and the Legislature's Select Water Committee toured the Upper Green River Basin Thursday.
The state has identified three lower basin sites - Sand Hill, McNish Wash and Church reservoir - that have the most potential for a dam and reservoir.
But the agency is considering several other sites high up in the basin in the foothills of the western slope of the Wind River Range.
Wyoming has rights to water in the Green River, but has not exercised them.
The state generates about 18 million acre feet of surface water each year. An acre foot is the amount of water needed to cover one acre of land one foot deep, or about 325,851 gallons. Under various interstate river compacts and court decrees, Wyoming is entitled to consume about 4 million of those acre feet. Right now the state uses 2.8 million, leaving 1.2 million acre feet available in areas such as the Upper Green River Basin.
Water officials believe more storage is needed, particularly for irrigators in the Green River Basin and for towns and communities such as Pinedale, Big Piney and Boulder that are growing due to southwest Wyoming's natural gas energy boom in the nearby Jonah and Pinedale Anticline fields.
Without more water, there won't be continued economic development and agricultural sustainability, officials contend.
Off-stream, wetlands
Using past water studies dating back to 1970, the state identified a variety of possible dam and reservoir sites, including the Green River Lakes at the edge of the Bridger Wilderness. Green River Lakes enlargement could impound 250,000 acre feet of water.
Other sites that have been examined and will be further explored in a new study include The Narrows on the Green River just above the Warren Bridge some 15 miles north of Pinedale; the New Fork Narrows on the New Fork River; and enlargements of the New Fork, Burnt Lake, Boulter Lake and Halfmoon Lake.
Lawmakers toured the Kendall site, the Green River enlargement site and the Warren Creek sites, all of which would include off-stream, or off-channel, dams and reservoirs. Each site would provide well in excess of 200,000 acre feet of water storage.
Off-channel reservoirs employ canals and sometimes diversion dams to move water from a stream or river to a new reservoir, which can be located miles away. On-stream reservoirs are created by building dams directly on a stream or river.
Carnevale told lawmakers the state would have a poor chance of getting federal approval for an on-stream dam and reservoir. The three Upper Green sites under consideration are all off-stream sites that would include extensive canal systems to feed the reservoirs.
"If you can show one hell of a lot of overwhelming need … a huge, foreseeable need and population growth, you might be able to convince the corps to permit an on-stream site, but it will be an extremely tough sell," he said.
But there's a downside to off-channel reservoirs, he said. Western Wyoming's harsh winter weather and the topography of the three sites would require lots of canal maintenance and could make it difficult to keep the reservoirs filled.
"It may be difficult to divert that water in the spring," he said. "With the maintenance of the canals plus the weather, it may be hard to fill the reservoir unless you build one hell of a canal."
Carnevale said projects that disturb wetlands as little as possible are also more likely to be permitted by the agency.
"The corps really puts the blinders on when it looks at wetlands … what damage the project will do to wetlands and can it be mitigated or avoided," he said. "The first cut the corps makes (on the state's permit application) will be the wetlands and stream channel impacts from this project."
Southwest Wyoming bureau reporter Jeff Gearino can be reached at 307-875-5359 or at gearino@trib.com.
About the sites
The Wyoming Water Development Commission recently contracted with Kleinfelder Inc. and TST Environmental Services Inc. for a more in-depth study that evaluates developing new reservoir storage in Green River Basin. Mike Carnevale of TST said the consultants examined 11 previous water storage studies written between 1970 and 2002 and came up with a list of 36 possible dam and reservoir site alternatives for the Upper Green River Basin above Fontenelle Reservoir. The study team pared the list down to 11 possible sites, and after further review, formulated three recommended alternatives:
Sand Hill Reservoir
* Location: The site is about five miles due west of Big Piney in Sublette County. Wyoming Highway 350, also known as Middle Piney Road, runs directly through the proposed dam site.
* Capacity: The reservoir would store about 14,500 acre feet of water. The reservoir would be impounded by an embankment dam with a height of 70 to 75 feet, and a crest length of about 2,800 feet.
* Supply: The drainage basin above the dam is about 6.3 square miles. Carnevale said the water supply for the site would be delivered through a 15,000-foot-long supply canal with diversion dams on both South Piney and Middle Piney creeks.
Estimated cost: $27 million.
McNish Wash Reservoir
* Location: The site is about nine miles northwest of Big Piney and Marbleton in Sublette County. It is also located about a mile west of the existing McNish Reservoir No. 1 and McNish Reservoir No. 2.
* Capacity: The reservoir would store between 5,000 and 10,000 acre feet of water. The reservoir would be impounded by an embankment dam.
* Supply: It would be fed by diversion canals.
* Estimated cost: $23 million.
Church Reservoir
* Location: The site is on the Church homestead just west of Boulder in Sublette County. The site lies along the western foothills of the Wind River Mountains.
* Capacity: The reservoir would store from 6,000 to 9,000 acre feet and would yield just over 5,000 acre feet of water.
* Supply: Water would be diverted from Gem Creek to fill the reservoir.
* Estimated cost: $10 million.