Pipestem Dam & Lake, North Dakota

Located north of Jamestown, N.D. on Pipestem Creek, Pipestem Dam was constructed for flood damage reduction, fish and wildlife enhancement, and recreation. Construction of the dam began in June 1971, and was completed in 1973. The dam measures approximately 4,000 feet in length, with a maximum height of 107.5 feet from the stream bed to the top of the dam. Also nearby is the Jamestown Dam and Reservoir, which is operated by the U.S. Bureau of Reclamation. 

Description

Pipestem Dam and Reservoir is owned, operated, and maintained by the U.S. Army Corps of Engineers. The dam includes an earthen embankment across Pipestem Creek, and a gated outlet structure through the embankment. The outlet gates allow for the controlled (although limited) release of water during flood events and the release of stored water during normal operations for recreation and to support fish and wildlife. Water also can flow over an earthen spillway if water levels exceed the capacity of the outlet structure.

Completed in 1973 on Pipestem Creek, it was the second of two dams built by USACE and the Bureau of Reclamation to reduce impacts from flooding on life safety and property in Jamestown, N.D. Water storage and its release from Pipestem Lake are coordinated with Reclamation who owns Jamestown Dam and Reservoir, about 6 miles east and in the James River Basin.

An Aerial Photo of Pipestem Dam & Lake

Maintaining the dam over time

As part of its Dam Safety Program, USACE Omaha District conducts detailed engineering analyses to ensure its dams reduce risks to the public, property, and the environment to the extent possible. Standards and practices that guide the Dam Safety Program are continually updated to improve the maintenance and operation of dams to ensure they can safely serve their original purposes. In addition, dam safety engineers across federal and state agencies share information as they learn about the performance of flood reduction structures built over many decades and use more precise, modern technologies and apply up-to-date science to reduce flood risk more effectively.

During the flooding of 2009, the spillway on Cottonwood Creek Dam south of Lamoure, ND, experienced severe erosion. (The dam is owned by the North Dakota Game & Fish Department.) USACE dam safety experts evaluated Cottonwood Creek’s spillway, which has similar geological materials and geometry to Pipestem’s spillway. Using tools and information developed since Pipestem’s original design in the late 1960s, this work allowed USACE to better understand the dam’s ability to withstand erosion. From this work, it was determined that under extreme flood conditions the original spillway with its similarly highly erodible sands and gravels poses an unacceptable risk of the progressive erosion of the spillway that could lead to a spillway breach and the uncontrolled release of water.

Managing flow to reduce risk

During periods of high runoff, most often during extreme storms when rain or snowmelt fill the reservoir, the outlet structure can release up to 2,300 cubic feet of water per second (one cubic foot of water is equal to 7.5 gallons). The Jamestown Dam outlet can release just over 2,700 cfs.  

The spillway has never been needed but it is designed to pass up to 50,900 cfs of water if the need to pass water from the reservoir exceeds the capacity of the outlet structure. For perspective, the record water releases in 2009 through the outlet structures at Pipestem and Jamestown dams were 1,420 and 1,807 cubic feet of water per second, respectively (3227 cfs total).

Pipestem Dam is operating as designed to reliably reduce flood risks, but it alone, or in conjunction with Jamestown Dam, cannot eliminate the risk of flooding. Even if streams and rivers below these two dams reach or exceed their capacity and when flow into the reservoir exceeds the outlet structure’s release capacity, water may flow over the spillway. This spillway flow is critical to reducing the possibility of water flowing over the dam that can lead to dam failure, or breach. A breach would allow the water stored behind the dam to flow uncontrolled downstream, further intensifying downstream flooding. This would impact critical infrastructure and downstream levee systems and put thousands of lives at risk in Jamestown and further down Pipestem Creek and the James River Basin.  

For more detailed information about the need for this project to address potential spillway erosion and a summary of the analysis of reasonable alternatives, the Draft Environmental Assessment for the Pipestem Dam Safety Modification Study is available here for reading or downloading:  https://usace.contentdm.oclc.org/digital/collection/p16021coll7/id/11048.

Taking action on current concerns

Omaha District evaluated several options to address the threat of spillway erosion and evaluation criteria included the effectiveness of any plan to reduce life safety risks. The selected plan will prevent the start and progression of erosion that could lead to a spillway breach and the uncontrolled release of water. In addition to studying the issues with the spillway, a team of structural engineers, geologists, and hydrologists evaluated additional ways to increase overall performance at the dam including the stability of slopes located along or near the spillway. Design of the construction plan is in its final stages and USACE anticipates a combination of spillway improvements to begin in spring 2023.