Design improvements for pumping plants minimize downtime in California
Most of the water used in Southern California comes from outside the region, and much of it is supplied by the Metropolitan Water District of Southern California, the nation’s largest provider of treated drinking water.
Metropolitan operates a complex conveyance, storage and distribution system consisting of aqueducts, pumping plants, reservoirs, distribution pipelines and other facilities. It imports water from the Colorado River and Northern California, via the State Water Project, to supplement local supplies. It then delivers this water through hundreds of miles of large-diameter pipelines and tunnels across 5,200 square miles (~13,500 square km) to 26 member agencies that, in turn, provide water to 19 million people in Los Angeles, Orange, Riverside, San Bernardino, San Diego and Ventura counties. The district also helps its member agencies develop water conservation, recycling, storage and other resource-management programs.
Maintaining Reliable Water Delivery
Metropolitan was formed in 1928 to build the Colorado River Aqueduct, and the system began operating in 1941. Water flows through most of the service area by gravity, but five pumping plants in the Mojave Desert are required to convey water on its 242-mile journey from Lake Havasu to its final destination, the CRA’s terminal reservoir, Lake Mathews in the foothills of the Temescal Mountains in Riverside County, California. To ensure infrastructure remains reliable, including the equipment at the pumping plants, Metropolitan manages a robust Colorado River Aqueduct maintenance and rehabilitation program.
There are nine pumps (three groups of three pumps) at each of the five major pumping plants along the Colorado River Aqueduct. The system is designed to use eight pumps at full capacity, allowing one pump to undergo periodic maintenance or standby for redundancy. The current practice for isolation of an individual pump unit requires three pumps at a pump plant — one group of pumps — to be removed from service at a time.
Significant cutting and welding activities are required to install a steel bulkhead in one pump’s 6-foot-diameter discharge line, and subsequently return two of the three pumps back into service. The sequence of activities must be repeated to return the one pump to service following maintenance or repair work. The existing process is difficult and time-consuming and requires lengthy flow reductions on the Colorado River Aqueduct.
Metropolitan staff addressed the labor-intensive process by developing an improved design using special couplings that are easier, faster, and less disruptive to install. This design also is more cost-effective to maintain and minimizes disruptions to water deliveries.
Breaking Down the New Design
Metropolitan’s pumping plants employ 4,300 hp to 12,500 hp pumps, each moving approximately 225 cubic feet per second (cfs) in a system that flows at 1,750 to 1,800 cfs, carrying 1.2 million acre feet per year into Metropolitan’s aqueduct. Conditions at the pumping plants vary. Strategically located along the route, the facilities were designed specifically to the conditions of each site.
The required lift from one plant to another varies from 291 feet at the Whitsett Intake, which is the starting point of the Colorado River Aqueduct, to 441 feet at the last plant, Julian Hinds, at the other end. Large 6-foot- and 10-foot-diameter steel pipes carry the water uphill at these pumping plants. Pipe wall thickness, diameters and pressure ratings are slightly different at each of these plants.
Adding to these design intricacies is the need to account for thermal movement caused by severe temperature swings in the desert. It is common to have large ambient temperature changes at these plants, with peaks near 120°F in the summer and lows significantly below freezing in the winter. These temperature swings cause thermal expansion in the pipes such that a 6-foot-diameter pipe can experience linear expansion ranging from 1/8 inch to 7/8 inch, depending on the length of pipe. The design had to accommodate for these large thermal variances. In some areas, the steel pipes were slightly out-of-round, which also had to be accounted for.
Constructability was another challenge that needed to be addressed.
“With many intricacies across the pumping plants, the design had to be universal when complete, yet adaptable during construction. The goal was to use parts that could be installed interchangeably among the plants and allow for the isolation bulkheads to be installed within a short work window,” said Metropolitan Project Manager Ish Singh.
The time constraints for installation were also important. Since the work had to be executed during a complete shutdown of the Colorado River Aqueduct system, component delivery and installation would have to take place within just four weeks.
One of the bigger challenges was finding a solution that allowed future rehabilitation to take place on a single pump without requiring the entire group of three pumps to be offline for a long period. Metropolitan staff rose to the challenge, identifying a solution that accommodated the desired functionality. With the design formalized, Metropolitan issued a request for bids and ultimately entered into a contract with JF Shea, which partnered with Victaulic on a construction project for the installation of the couplings.
Project Execution & Benefits
The project to implement the new design was carried out at all five pumping plants. These couplings provide a more efficient method of isolating a single pump than previous processes, minimizing the downtime for the plants to function at full capacity.
“The design used a removable spool with a grooved coupling on one side and an unrestrained coupling on the other side. The removable components were designed and constructed with uniform diameters and tight tolerances for interchangeability between the various pumping plants,” said Armen Kutyan, Metropolitan mechanical engineer.
The performance characteristics of Victaulic’s flexible grooved coupling provide the necessary strength and allowed for easy installation, while the unrestrained coupling allows for the required thermal expansion at each joint. The couplings also promote efficiency in installation and simplicity in removal for future rehabilitation projects at the pumping plants. The removal of the couplings and installation of the isolation bulkheads at the Metropolitan plants will now take about 12 hours rather than 40 hours, as previously required.
Efficiency is essential, as the annual Colorado River Aqueduct shutdown takes one month, which created a firm and aggressive schedule for the project. Installation of the couplings at all five pumping plants was phased over two years during successive one-month shutdowns. This project is an initial step to a broader effort spearheaded by Metropolitan to rehabilitate its infrastructure at all five pumping plants to ensure long-term reliability. The new design will streamline the isolation process by using interchangeable couplings at all the plants, simplifying product sourcing and reducing maintenance costs.
Investing in Reliability
Metropolitan has supported programs over the years to promote reliability, including investing in storage, funding development of local supplies, and helping the region conserve in an environmentally and economically responsible manner.