Graders and scrapers are busy conducting earthwork on a sandy parcel in Hilmar in hopes of completing Turlock Irrigation District’s Lateral 8 Regulating Reservoir Expansion Project before the 2016 irrigation season begins.
“If the rain keeps coming—which I hope it does—we plan to have the expansion completed before the irrigation season in March,” said TID engineer Matt Hazen. “However, the Board will ultimately decide when the season will start.”
As detailed in the scope of the project, the enlarged facility will continue to serve as a surface water regulation facility used to stabilize agricultural irrigation flows to TID customers within District boundaries. It will also present the potential for increased water savings since the project is expected to increase reservoir storage capacity from 29 acre-feet to 130 acre-feet.
The expansion will allow for the capture of a majority of the spills on the Highline Canal at approximately 9,000 acre-feet, which is a significant increase from what the current facility is capable of at approximately 2,550 acre-feet during an average year of rain.
“This will allow us to save more water that would normally be sent to the river, while increasing customer service on the bottom end of the system,” said spokesperson Calvin Curtin. “Regulating reservoirs are on the mind of a lot of irrigation districts in California right now.”
In April of last year, TID completed construction of the Lateral 8 Regulating Reservoir, which is located near the end of the Highline Canal in Hilmar. The project, which was constructed by renovating an old waste water treatment facility that was purchased from the Hilmar County Water District, goes in conjunction with the Lateral 8 Total Control Channel Pilot Project to capture spillage and deliver only the amount of water that is needed for customers.
Given the success of the existing reservoir with capturing a sizeable amount of water during the 2015 irrigation season, the Irrigation Capital Planning Team chose to implement plans to enlarge the facility. TID owns approximately 25.5 acres of property on which the current seven-acre reservoir sits, and the original design also included elements to facilitate an expansion of the reservoir to cover the entire property.
Hazen said that the District has not had to contract out for the project, as TID has been able carry out all aspects of the expansion in-house so far.
“They are doing a fantastic job with the project,” said Hazen. “They are on time and on budget.”
Two additional pumps will be installed at the existing pump facility as part of the expansion in order to increase output flow potential. As a result, Lateral 7 output capacity will increase from 20 cubic feet per second (cfs) to 60 cfs, while Lateral 8 output capacity will increase from 20 cfs to 40 cfs.
As with the existing regulating reservoir facility, the expansion will continue to receive water from the concrete lined Highline canal, store the water in the regulating reservoir, and—when needed—pump the water back to the Highline canal or Lateral 7 to supplement existing flows.
Hazen said that following the completion of earthwork next month, TID crews will progress to lining the interior embankment slopes of the reservoir with 138,000 square feet of concrete that will be poured three inches thick. This will be used to prevent loss of water captured by the reservoir into the groundwater table below it, an amount that is estimated at approximately 1,835 acre-feet during an average year.
“We wanted to make sure we really captured all the water and not lose any to infiltration,” said Hazen.
In addition to the numerous benefits associated with the expansion, driving factors for the project include the recent drought, demonstration of the District’s continuing commitment to water savings, and cost to benefit ratio of expansion exceeds the original Lateral 8 Regulating Reservoir.
“We’re looking forward to seeing how it does this year,” said Hazen. “We adjusted all of the kinks during the drought year, and hopefully we’ll have more water to work with this year.”