Hey, Answer Girl,
I’d Like to know some history about the LaPrele dam between Casper and Douglas near the natural bridge. — Esther
The LaPrele dam is located on LaPrele Creek, about 11 miles southwest of Douglas near Ayres Natural bridge. It is privately owned by the LaPrele Irrigation District, which is composed of area ranchers.
It was built by the LaPrele Ditch and Reservoir Co. under the Carey Act of 1894, in which the federal government gave land to arid, Western states to be irrigated to promote settlement.
The Ambursen Hydraulic Construction Co. of Boston, Mass., began constructing it in 1906, completing all but the top 40 feet of the dam, which was built under the direction of Pat Mulcahy. The hollow, concrete ambursen-style dam was finished in 1909. It stood 137 feet high, 325 feet long and had a capacity of 20,000 acre feet of water.
The cost of the dam was $650,000, and the cost of the ditches was about $350,000.
The LaPrele Ditch and Reservoir Co. was absorbed by the North Platte Valley Irrigation Co. before the irrigation ditches were complete. This company planned to expand irrigation toward Glenrock by an additional 50,000 acres.
It spent $2 million building a a two-story concrete powerhouse near Ayres Natural Bridge, a pumphouse near Glenrock and a wooden pipe to transport the water.
The decision to expand was based on surveys conducted in 1905, but either the surveys were wrong or water levels dropped.
“By the time they got the dam finished, there wasn’t enough water,” said Larry Crummer, board member of the LaPrele Irrigation District from 1986 to 1987 and president from 1988 to 1994.
The company went bankrupt and abandoned the powerhouse and pumphouse. You can still see the powerhouse, a shell of a building with broken windows and a roof that has long since fallen in, near the entrance to Ayres Natural Bridge park.
A man named C.C. Carlysle was appointed to manage the dam in 1912 until the Douglas Reservoirs Company purchased it in 1918. In 1922, the LaPrele irrigation project was turned over to the settlers, who have since managed it under a number of organizations, such as the Douglas Water User’s Association.
By the early 1970s, the dam was in dire need of repair. The Douglas Budget reported that it “was near condemnation because it did not meet the current safety criteria of the National Dam Inspection Act.” The state engineer required the water level of the dam be kept low for safety reasons.
The capacity was 20,000 acre feet of water, but it held less than half that in 1970. It was far from enough water to irrigate crops in the area. The LaPrele Irrigation District didn’t have enough money to fix it, and state and U.S. government agencies didn’t want to chip in.
Around 1977, Panhandle Eastern Pipeline Co. agreed fix the dam in return for a share of the water to be used in a coal gasification project.
Over the course of two years, cracks were grouted with rock and earth, the dam was completely resurfaced and it was anchored to the foundation bedrock with post tensioned rock bolts. Originally, the spillway simply went over the dam, but tunnels were dug to divert the spillway, making it safer.
This was quite a feat considering the terrain. Mel Nelson and Ed Baker, current board members of the LaPrele Irrigation District, took me on a tour of the dam Friday. To get to the top of the dam, we had to drive up a narrow, switchback road made of large rocks with steep edges. I would not have wanted to drive up there in a big construction truck, that’s for sure.
In 1979, the American Society of Civil Engineers awarded the LaPrele Irrigation District, the Panhandle Eastern Pipeline Company and the DMJM-Phillips-Reister-Haley Inc. engineering firm the “Outstanding Civil Engineering Achievement of 1979.”
The repairs cost Panhandle Eastern Pipeline Co. $4.5 million, but the company abandoned the coal gasification project and never came calling for its share of the water.
Today the LaPrele dam holds 21,000 acre feet of water and irrigates 14,612 acres of land, according to the 2010 Wyoming Irrigation Systems Report by the Wyoming Water Development Commission.
Special thanks to Vincent Crolla, archives specialist at the Western History Center in Casper, for providing several articles from the Douglas and Casper newspapers from the 1970s on the repair of the dam; Larry Crummer, of Douglas, for sharing his copy of a 1936 article in the Douglas Enterprise detailing construction of the original dam and other documents; the Wyoming Pioneer Museum in Douglas for sharing documents and photos; Mel Nelson for loaning me his copy of “Pages from Converse County’s Past” by the Wyoming Pioneer Association in Douglas; and both Nelson and Ed Baker for giving me a tour of the dam.
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Answer Girl tackles questions about Casper, the universe and everything else. Submit your questions by email to Carol Seavey at email@example.com, call her at 307-266-0544.
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