Piece Pipe

Aug. 6, 2003
South Dakota's Mni Wiconi Rural Water Engineering Project incorporates high-density polyethylene pipe into the largest water engineering effort in the U.S.

About the author: Drew Wilson is a writer and photographer for McElroy Manufacturing and covers polyethylene pipeline stories as a freelance writer. For further information, contact McElroy at 918-836-8611.


A little more than 100 years ago, the Sioux Warriors protected their sacred Black Hills in South Dakota with bow and arrow. Today, the Great Sioux Nation is protecting the same area, but their methods are slightly different--essentially, it can be described as part of the largest water engineering effort in the U.S.

The Mni Wiconi Rural Water Project (Mini Washonee) is the world's largest rural water pipeline and will eventually supply water to the Lower Brule, Pine Ridge and Rosebud Reservations as well as the West River/Lyman-Jones Rural Water System, which serves residents located in nine counties outside of the reservations.

The development of this massive water supply project was based on a need assessment and final engineering report carried out under the supervision of the federal government. It was authorized by Congress in 1988 and expanded in 1994 to include the Rosebud and Lower Brule Sioux Tribes.

Over time, project costs have risen to almost $400 million with about 80% of the costs allocated to the tribal systems as non-reimbursable federal costs. Accordingly, the West River/Lyman-Jones Rural Water System pays a cost share on their portion of the project.

$400 million dollar question

When the Mni Wiconi Rural Water Project is completed in 2008, it will include over 4,300 miles of transmission and distribution pipelines, a water treatment plant, booster stations, and numerous reservoirs. Because of the size and cost of the project, construction is currently being done in various phases.

Currently, Phase XII of the project--the Rosebud Sioux Rural Water System--is under construction and this particular phase involves a significant quantity of high-density polyethylene pipe.

In addition to its role in two river crossings on Phase XII of the project, the polyethylene pipe also was a key factor in the massive intake system integrated into the Missouri River near Pierre, S.D.

"During the last several years, polyethylene has really helped us develop a niche in being able to perform almost any kind of pipeline work," said engineer Mark Morris, project manager and prime contractor for Phase XII of the Mni Wiconi Rural Water Project.

Morris, whose specialty is highway heavy utility construction with roots in agriculture, is very familiar with polyethylene pipe.

He's been involved with the installation of several large irrigation intake systems on the Missouri River utilizing polyethylene pipe, including the design of the Mni Wiconi intake line which incorporated polyethylene pipe and a siphon concept.

The siphon line consists of 2,600 ft of 42-in. polyethylene pipe and can handle an estimated 10 million gallons per day. A trench for the pipe was dug out in the river bottom using an excavator stationed on a barge. The pipe was then secured to the river bottom with 5,500-lb concrete anchors that were drilled into the riverbed approximately every 15 feet.

The original intake design called for ductile iron pipe, along with several large air/vacuum stations. These stations are to be installed down the middle of the causeway leading out to a peninsula known as Echo Point.

Rather than excavate through the causeway and risk losing portions of the causeway due to hydraulic pressure, and to keep the environmental impact to an absolute minimum, Morris submitted the siphon system as a value-engineering proposal.

Ultimately, the proposal was accepted and not only allowed for more water, but also saved the owner approximately $200,000.

"Once polyethylene pipe is in the riverbed it's there for good, you don't ever have to worry about it," said Morris. "With polyethylene pipe, there is no rusting, no leaks at joints and the pipe won't freeze and burst."

Morris pointed out that the installation is also a big advantage.

"All we had to do was excavate the ditch, float the pipe out and sink it," said Morris. "You can't do that with the other kinds of pipe."

Character strengths

To prevent the freeze and rupture of other piping materials on intake systems in the north, the pipeline must be pulled from the river during the winter months. With the polyethylene pipe, the intake can be a permanent structure because a freeze will not cause the pipe to burst.

Perhaps, the strong characteristic of the pipe is the way in which it is joined.

The pipe is heat fused together and the joints are as strong as the pipe itself. The pipe becomes a monolithic structure with no connections, therefore, essentially eliminating the risk that the connections could become potentially weak over time and leak.

The two river crossings for Phase XII of the Mni Wiconi Rural Water Project originally called for directional drilling, but Morris decided to use an open cut method because the riverbeds consisted of shale and the water depth was only about three feet.

"Because the riverbed was solid shale, we were able to save quite a bit of money by doing an open cut," said Mike Lee, project manager of Phase XII. Lee supervised almost all of Morris' rural water pipeline projects and agreed that the polyethylene pipe was the correct choice for this particular application.

As water shortages continue to become the norm and polyethylene pipe becomes more recognizable and reliable, the latter may one day ease the pain of the former.

For now, engineers and environmentalists alike are applauding the Sioux Nation for its pioneering efforts involving the use of polyethylene pipe.

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