Work is in the final stages to develop a low lake level pumping station at Lake Mead to further ensure adequate water will be available in the most populous area of Nevada.
For nearly 20 years drought conditions in the Colorado River Basin have caused Lake Mead to drop nearly 130 ft. In Southern Nevada, conservation efforts have reduced per capita use by 36 percent even as the population increased by more than 650,000 during the same period.
Now work is in the final stages to develop a low lake level pumping station at Lake Mead to further ensure adequate water will be available in the most populous area of Nevada. Approved by the Southern Nevada Water Authority (SNWA) Board of Directors in May 2015, the $650 million project was awarded to Barnard of Nevada in September 2015, with completion expected in 2020.
"When finished, this will enable us to access water under very low lake levels," said Erika Moonin, project manager of SNWA. "The pump station is designed to operate at low lake level, from 875 feet above sea level to 1,060 above sea level. If lake comes up we can switch back to other pump stations. But under very extreme low lake levels we will still have access to the community's water supply."
The main components of the new pumping station include 34 well shafts more than 500 ft. deep and 6 ft. in diameter to accommodate the pumps; a 26-ft. diameter access shaft; and an underground forebay 36 ft. high by 33 ft. wide by 377 ft. long. The flow rate of the pumping station will be more than 900 million gal. per day.
The new pump station is located on Saddle Island on the shores of Lake Mead and required significant underground work, posing challenges and risks.
"The fact that our low lake level pumping station includes an underwater canyon posed inherent risk with underground construction," Moonin said. "Another element are the deep-set submerged pumps. These are some of the largest in flow, capacity and total lift in the world. These pumps, because they are unique, called for a lot of work up front. It required extensive testing, before we agreed to purchase the pump.
"One of the unique things with these pumps is the manufacturer required tight tolerance on the plumbness of the well shaft. They needed to be vertical. One of the designs from the manufacturer relies on the flow of the water around the motor for cooling before it goes into the pump. Some of the pumps are 25 feet in total length. The shaft and the drilled well shafts are 500 to 530 feet in depth. Getting very straight well shafts is very difficult at that depth."
Equipment at the worksite included a specially built blind bore drilling rig for drilling the well shafts. Each shaft required three passes. A directionally guided drill bit was used to create the first hole which served as a pilot hole. It was then reamed out with larger bits until it was 91 in. in diameter.
The project is currently on schedule and under budget, said Bronson Mack, spokesman of SNWA. Its completion will no doubt be a significant achievement for southern Nevada and beyond.
"The southern Nevada Valley is home to 2.2 million people, which represents about 73 percent of the state's population. This valley is responsible for about 75 percent of Nevada's economic output. Ensuring a reliable water supply and access to water supply is paramount not just to the local economy but the state economy." CEG
By the Numbers
- Surface facility — elevation 1261 ft.
- Lowest lake water level pumping capability: elevation 870 ft.
- Flowrate of 900 million gal. per day (mgd) (600 to AMSWTF, 300 to RMWTF), expandable to 1,200 mgd
- 34 6-ft.-diameter well shafts, 505 ft. deep, in two rows of 17 each, blind bore method (North American Drillers major subcontractor)
- Surface building for electrical and controls
- 26 ft. diameter, 528 ft. deep (from elevation 1261 ft. to elevation 733 ft.)
- 377 ft. long, 33 ft. wide, 36 ft. height
- Number of pumps — 22 low lift, 12 high lift
- Pump design flow — each 20,835 gpm, or 30 mgd constant speed
- Pump design head – 435 ft.
- Pump brake HP – 3,050
- Pump setting — approximately 870 ft. elevation
- Two 12-ft. diameter aqueducts totaling approximately 6,500 linear ft. of 144-in. diameter pipe
- Two isolation valves/vaults on large diameter aqueduct (valves and fittings procured by SNWA)
- One blow off structure on large diameter aqueduct
- Two air relief valves on large diameter aqueduct