Location: North of Jamestown, N.D. on Pipestem Creek

Pipestem Dam and Reservoir is owned, operated, and maintained by the U.S. Army Corps of Engineers. 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 also in the James River Basin. The dam includes an earthen embankment across the river and a gated outlet structure through the embankment and an earthen spillway.

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Dam operators store water behind Pipestem Dam during periods of high runoff, most often during extreme storms when rain or snowmelt fill the reservoir. When flows in rivers and streams below the dam are lower, a gated outlet structure in the dam’s earthen embankment releases water into Pipestem Creek.  Operators release stored water during normal operations for recreation and to support fish and wildlife. 

The outlet is designed to release up to 2,300 cubic feet of water per second (cfs). For perspective, the largest release of water as a result of flooding was approximately 1,420 cfs from the outlet structure in 2009. (One cubic foot of water is equal to 7.5 gallons.)

The spillway’s role

If reservoir levels from extreme storms or snowmelt exceed the outlet’s release capacity and water rises high enough in the reservoir, water will flow through the spillway to reduce the possibility of water flowing over the dam embankment. This overtopping can lead to dam failure and intensify downstream flooding, putting thousands of lives at risk and impacting critical infrastructure.

The Pipestem Dam spillway is designed to pass up to 110,000 cfs. This large but intentional flow is a ‘non-breach’ release. The reservoir has never been high enough for spillway flow. It is important to understand that the dam is designed to release far more water when necessary.

As part of its Dam Safety Program, USACE Omaha District conducts detailed engineering analyses to understand and 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 USACE dams to ensure they reliably serve their original purposes. Dam safety engineers across federal and state agencies also share information about the performance of flood reduction structures built over many decades and they use more precise, modern technologies and apply up-to-date science to reduce flood risk more effectively.

During flooding in 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, USACE better understands the dam’s ability to withstand erosion. From this, it was determined that under extreme flood conditions the original spillway, with its highly erodible sands and gravels, presents an unacceptable risk of progressive spillway erosion that could lead to a spillway breach and the uncontrolled release of water.

Omaha District evaluated several options to address the threat of spillway erosion. The selected plan will prevent the progression of erosion under extreme flow that could lead to a spillway breach. In addition to studying 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. A multi-stage construction project is now underway to improve the spillway’s reliability and add these new features.

The level of flood reduction that the dam can provide will remain the same for which it was originally designed. Both the Pipestem and Jamestown dams play significant roles in reducing flood risk, but they cannot eliminate it.