An Idea That Didn't Hold Water
It seemed like a good Idea at the time. Build a nice little dam in a short deep canyon and provide water and flood protection for nearby farms. That's the kind of stuff US Bureau of Reclamation and Army Corps Engineers dream about. So, in the case of the Anchor Dam on Owl Creek in Wyoming, engineering desires and political expediency overrode the geologic reality. Farmers and residents knew that the canyon had caves and fractures. They knew that irrigation ditches in the area some times leaked or that water in creeks and ditches sometimes suddenly disappeared into gaping holes. But their warnings went unheeded. Geologists who studied the project were cautious but downplayed the risks. Some even dismissed the risks all together. They recommended further studies and investigations which were not conducted. Project engineering planning moved "full steam" ahead with most believing the engineers could and would solve any pesky problem the earth could throw at them.
In reality, though, the dam site had several inter-related geologic problems. It was located on the limb of the Anchor Anticline. Folding and faulting of the anticlinal structure resulted in a pattern of fractures and joints that would allow water to penetrate the rocks. The rocks of the area include 4 rock types known for dissolving or dissolutioning in water to form caves and or sinkholes: limestone, dolomite, anhydrite, gypsum. Gypsum layers and anhydrite layers in the Triassic Chugwater Formation and Permian-Triassic Goose Egg formation can dissolve in water and cause collapses called sinkholes. Dolomite and limestone are both carbonates chemically and are well known as cave prone lithologies. In the Anchor area, dolomite is found in stringers in the Pennsylvanian Tensleep sandstone while limestone and dolomite make up much of the Triassic Dinwoody and Permian Phosphoria. The last two inter-finger with stringers of Goose Egg red beds in the area. The limestone and dolomite dissolves along fractures forming cave networks. There were already open fissures and caves formed along the fractures. The area has several prehistoric sinkholes from the dissolutioning of limestone, dolomite, gypsum and anhydrite that were filled in with alluvium. These older sink holes can sometimes still actively take fluid.
The subsurface geological studies that could have better defined the risks listed above were never done. In hind sight, these technical issues should have delayed or canceled the project. They did not, but the project was delayed by political issues that held up construction of the dam from the late 1940s till 1957. The project originally called the Owl Creek project and Embar project was delayed over water rights and US law that requires farms participating in the water from the reclamation projects to be less than 320 acres for 1 individual and 640 for a husband and wife. At high elevation in Wyoming's cold, dry climate, a cattle ranch of that size is not profitable.. Most of the ranches in the area were quite a bit bigger. The Wyoming Congressional Delegation, led by Senator Frank Barrett, came to the rescue. They got a bill passed that exempted the Wyoming landowners from the acreage restrictions. Finally enough ranches joined the irrigation district to justify the project.
In 1957 work commenced on the dam. Problems started right away. The original site had to be abandoned when large fractures and small caves were found in the dolomite inter-beds within the Pennsylvanian Tensleep Sandstone. The dam location was moved some distance upstream to near the head of the canyon. As they dug into the canyon walls at the new site, 2 large caves were discovered. The cavities were filled using more than 2,000 cubic yards of concrete. Several similar cavities were found both on the canyon walls and in the soon to be flooded valley and they too were filled. After three years and a price tag of 3.4 Million Dollars the 208 foot-high dam was completed on Oct. 26, 1960. The project was $116,000 over budget.
The reservoir started to fill the following spring but within a few days it started to drain through previously unknown sinkholes and permeable fractures. The Bureau of Reclamation (BOR) moved to seal off the leaks by pumping cement or building levees around them. This pattern would be repeated over the next few years. Finally after a decade of attempted remediation, the final price tag exceed over 7 Million dollars. Fifty-four sinkholes had been plugged or levied off and yet still the reservoir leaked and held very little water. The BOR gave up! The final score: Earth1, Engineers 0. To this day the reservoir still holds a very little water.
What is amazing to me is how few people know this story. Very few residents of the Bighorn Basin are aware of the reservoir's failure. The campground is gone, picnic area is gone; boat ramp is gone and most of the BOR signs except for those saying "no trespassing" are gone. The lake did partially fill one particularly wet spring when inflow was greater than leak out. A photograph was taken, and of course, became the cover photo for BOR documents about the dam. Though they admitted in private and in internal memos that the project failed, BOR personnel covered the story up in public. The even classified the project as research so they could hide some of the expenditures from prying congressional and public eyes. It worked. A white elephant sits in the Anchor Anticline Canyon and no one seems to see it. A monument to good intentions and government waste!
An Idea That Didn't Hold Water
It seemed like a good Idea at the time. Build a nice little dam in a short deep canyon and provide water and flood protection for nearby farms. That's the kind of stuff US Bureau of Reclamation and Army Corps Engineers dream about. So, in the case of the Anchor Dam on Owl Creek in Wyoming, engineering desires and political expediency overrode the geologic reality. Farmers and residents knew that the canyon had caves and fractures. They knew that irrigation ditches in the area some times leaked or that water in creeks and ditches sometimes suddenly disappeared into gaping holes. But their warnings went unheeded. Geologists who studied the project were cautious but downplayed the risks. Some even dismissed the risks all together. They recommended further studies and investigations which were not conducted. Project engineering planning moved "full steam" ahead with most believing the engineers could and would solve any pesky problem the earth could throw at them.
In reality, though, the dam site had several inter-related geologic problems. It was located on the limb of the Anchor Anticline. Folding and faulting of the anticlinal structure resulted in a pattern of fractures and joints that would allow water to penetrate the rocks. The rocks of the area include 4 rock types known for dissolving or dissolutioning in water to form caves and or sinkholes: limestone, dolomite, anhydrite, gypsum. Gypsum layers and anhydrite layers in the Triassic Chugwater Formation and Permian-Triassic Goose Egg formation can dissolve in water and cause collapses called sinkholes. Dolomite and limestone are both carbonates chemically and are well known as cave prone lithologies. In the Anchor area, dolomite is found in stringers in the Pennsylvanian Tensleep sandstone while limestone and dolomite make up much of the Triassic Dinwoody and Permian Phosphoria. The last two inter-finger with stringers of Goose Egg red beds in the area. The limestone and dolomite dissolves along fractures forming cave networks. There were already open fissures and caves formed along the fractures. The area has several prehistoric sinkholes from the dissolutioning of limestone, dolomite, gypsum and anhydrite that were filled in with alluvium. These older sink holes can sometimes still actively take fluid.
The subsurface geological studies that could have better defined the risks listed above were never done. In hind sight, these technical issues should have delayed or canceled the project. They did not, but the project was delayed by political issues that held up construction of the dam from the late 1940s till 1957. The project originally called the Owl Creek project and Embar project was delayed over water rights and US law that requires farms participating in the water from the reclamation projects to be less than 320 acres for 1 individual and 640 for a husband and wife. At high elevation in Wyoming's cold, dry climate, a cattle ranch of that size is not profitable.. Most of the ranches in the area were quite a bit bigger. The Wyoming Congressional Delegation, led by Senator Frank Barrett, came to the rescue. They got a bill passed that exempted the Wyoming landowners from the acreage restrictions. Finally enough ranches joined the irrigation district to justify the project.
In 1957 work commenced on the dam. Problems started right away. The original site had to be abandoned when large fractures and small caves were found in the dolomite inter-beds within the Pennsylvanian Tensleep Sandstone. The dam location was moved some distance upstream to near the head of the canyon. As they dug into the canyon walls at the new site, 2 large caves were discovered. The cavities were filled using more than 2,000 cubic yards of concrete. Several similar cavities were found both on the canyon walls and in the soon to be flooded valley and they too were filled. After three years and a price tag of 3.4 Million Dollars the 208 foot-high dam was completed on Oct. 26, 1960. The project was $116,000 over budget.
The reservoir started to fill the following spring but within a few days it started to drain through previously unknown sinkholes and permeable fractures. The Bureau of Reclamation (BOR) moved to seal off the leaks by pumping cement or building levees around them. This pattern would be repeated over the next few years. Finally after a decade of attempted remediation, the final price tag exceed over 7 Million dollars. Fifty-four sinkholes had been plugged or levied off and yet still the reservoir leaked and held very little water. The BOR gave up! The final score: Earth1, Engineers 0. To this day the reservoir still holds a very little water.
What is amazing to me is how few people know this story. Very few residents of the Bighorn Basin are aware of the reservoir's failure. The campground is gone, picnic area is gone; boat ramp is gone and most of the BOR signs except for those saying "no trespassing" are gone. The lake did partially fill one particularly wet spring when inflow was greater than leak out. A photograph was taken, and of course, became the cover photo for BOR documents about the dam. Though they admitted in private and in internal memos that the project failed, BOR personnel covered the story up in public. The even classified the project as research so they could hide some of the expenditures from prying congressional and public eyes. It worked. A white elephant sits in the Anchor Anticline Canyon and no one seems to see it. A monument to good intentions and government waste!