Southern Nevada Water Authority (SNWA) diversions from Lake Mead were in jeopardy due to drought conditions in the West, causing historically low water levels. The Authority was concerned that their intake structure might surface if water levels continued to drop.
The first diversions of Lake Mead water occurred in 1934 when pumping to Boulder City began from a plant inside Hoover Dam. In April, 1942, water was diverted from Lake Mead for war effort plants in Henderson, Nevada. With declining groundwater levels, large diversions for the Las Vegas Valley began in January, 1984, through the Southern Nevada Water Project diversion at Saddle Island. In 1991, the Southern Nevada Water Authority was established to address regional water issues. The Water Authority is committed to managing the region’s water resources and developing solutions to ensure adequate water supplies for the future. The Southern Nevada Water Systems (SNWS), which began operations in 1971, comprises the Water Authority’s system to pump, treat, and deliver water from Lake Mead. SNWS was officially transferred from the federal government to the Authority in 2001.
To protect the Agency from experiencing problems with their intake capabilities, the SNWAengaged CH2M Hill to design an intake structure with sufficient depth to ensure that continuing drops in water levels on the lake would not compromise their ability to obtain water through the intake. CH2M Hill’s design lowered the intake structure to approximately an elevation of 978 feet from the existing elevation of 1,051 feet. The design called for manufacturing 176 feet of 145 1⁄4 -inch OD steel pipe including a tee with a 145 1⁄4 -inch x 120-inch OD reducer and 12 feet of 120-inch OD pipe. The design also required two 30- degree elbows and a 1671⁄4 -inch OD intake pipe. Pipe was lined and coated with polyurethane and cement mortar was added to the exterior coating for mechanical protection. Agrout packer, inserted in the interior of the 120-inch section, was also required. Not only was the project complex in scope, delivery was critical. The proposals were called for in December, 2003, and delivery of all piping, fabricated fittings, appurtenances, and hardware was required 3 1/2 months later. Liquidated damages were $1,000 per day. The SNWA reviewed the delivery schedules submitted in bid packages. Northwest Pipe Company’s years of industry experience, success on past projects, and ability to deliver led the Agency to choose Northwest Pipe over other competitors. Northwest Pipe’s ability to deliver on time was enhanced by its multiple ISO 9001:2000-certified manufacturing facilities, making the Company an ideal choice for delivery of a quality product. Since on-time delivery was essential, Northwest Pipe utilized two facilities to manufacture the pipe and fittings. The 120-inch pipe and 1451⁄4 -inch tee were produced at the Saginaw, Texas, facility. The 145 1⁄4 -inch pipe, elbows, and miscellaneous appurtenances were produced at the Adelanto, California plant.
Installation of the intake modifications was complex, since the entire pipeline was underwater. The tee was shipped to the jobsite intact. Leveling pins were used to level the tee on the pad. The tee was then submerged and towed out to its final position, placed in an existing vertical tunnel, with an 120-inch leg placed in the vertical tunnel. The bladder was later placed in the 120-inch pipe segment. Seven 145 1⁄4 -inch pipe segments, including the 167 1⁄4 -inch increaser, were pre-assembled on shore. The 347,700-pound welded segment was then towed into position, attached to the tee with the special Carnegie section, and bolted with a series of restrained lugs. The final installation component involved attaching the 20,000-pound bar screen under water. Again, shore-based preparations enabled installation with just two connection made under water.
When Southern Nevada Water Authority needed a solution to an emergency situation they turned to welded steel pipe manufactured by Northwest Pipe Company. By working with the owner, engineer and the installing contractor, Northwest Pipe Company ensured a high-quality pipe delivered on time for this critical project.