5-Mar-09 9:30 PM CST
Instant Water: An Irrigation Automation System Delivers
Everybody knows it never rains in sunny southern California. That’s why farmers there, whose crops require a substantial supply of water, rely on snow to irrigate the fields. It doesn’t snow there either, but it does hundreds of miles to the north and to the east. Here, on the slopes of the Cascade and Sierra Nevada Mountains, technicians from the US Bureau of Reclamation (Reclamation) venture each winter and early spring. Its mission is to measure the depth and water content of the mountaintop snowfalls that later in the year will become an important source of water.
Runoff from the melting snows of these summits is conveyed southwards through the summer months, negotiating dams, deltas, rivers, and canals to reach thirsty farm fields. And that information gathered by the technicians comprises critical data needed to prepare water allocation schedules for the demands of southern California’s extensive agricultural economy.
However, lately, it is becoming increasingly difficult to meet the demand.
According to Reclamation, which manages federal water projects in the western states, recent dry spells have curtailed water supplies throughout the region. It also reports that this year’s snowpack water content for the state of California on May 1 was only about 65% of average, while the corresponding figure for the previous year was only about 25% of average.
Beyond this, new constraints on water availability have emerged. For example, the gigantic pumps operated by the state of California and the Reclamation to propel water southward from the San Joaquin-Sacramento Delta, have been placed under seasonal restrictions by court order to protect the delta smelt, a threatened fish species native to that rare and highly prized ecosystem. Meanwhile, momentum has been building to implement broader restrictions on federal and state water development projects to protect additional fisheries and aquatic species. According to Reclamation, these restrictions, combined with the recent dry weather patterns in the western states, are expected to reduce 2008 water allocations to users in California by up to 30%.
These pressures, combined with regional growth in residential development and demands from business and industry, all point to tighter water supplies in the future.
With California’s highly successful agricultural sector virtually dependent on irrigation, water users are now beginning to focus on water efficiency initiatives. By making use of sophisticated techniques such as drip irrigation and tailwater reuse systems, and by switching to water-frugal crops, farmers continue to make the desert bloom, delivering a wide range of crops including tomatoes, grapes, lettuce, and almonds.
In the Middle
Feeling the pressure of tightening supply, the region’s water purveyors have undertaken initiatives to complement the efforts of growers. But for water providers, along with the goal of conserving a precious resource, come the goals of improved service delivery and profitable operations. At the end of the irrigation season in 2005, Central California Irrigation District (CCID) initiated an irrigation canal modernization and automation project. CCID owns about 250 miles of gravity-fed canals, through which it manages water deliveries to over 600 customers in an area extending along I-5 corridor from Crow’s Landing to Mendota in Fresno County. Its recent project was designed to increase water efficiency, service quality, and profitability throughout the CCID network of irrigation canals serving farmlands in California’s Central Valley.
Water pumped into the Delta-Mendota Canal—and carried 117 miles southwards from the Tracy pumping stations on the Sacramento–San Joaquin Delta—is stored in the Mendota Pool in Fresno County, and provides the source from which CCID and various other water contractors supply water to farms in the region. Water entering CCID’s two major supply canals, known as the main and outside canals, at the head in Mendota, then becomes available for distribution to agricultural users along the CCID irrigation canal system’s 110-mile course.
However, according to Dr. Charles Burt, Chairman of the Board for the Irrigation Training and Research Center (ITRC) at California Polytechnic State University (Cal Poly), the lengthy canal network has suffered from a built-in inefficiency.
“Water released from the Mendota Pool could take up to two days to reach users at the far end of the canal system,” he says.
“An irrigation canal is not like a faucet at home,” explains Burt. “You can’t just turn a faucet, and turn the water on and off at will.”
|Photo: Central California Irrigation District|
Water pumped into the Delta-Mendota Canal is stored in the Mendota Pool in Fresno County, and provides the source which CCID and various other water contractors supply water to farms in the region.
Likewise, Burt says quickly shutting off the flow once the demand has been satisfied can be equally problematic. “On the main canal, the flow rate is 600 cubic feet per second—that’s 300,000 gallons of water per minute, contrasted to a showerhead, which delivers only 2 gallons per minute,” he says. “It’s not a game; bad things can happen—if you don’t control the flow properly, it can overtop the canal. If you see a spill at the end of the canal, it’s already too late to do anything about it at the head.”
Putting aside the issue of a catastrophic overflow, he says, “It’s the day-to-day operational losses that add up. If you don’t have very good control of water, you could be short on deliveries sometimes and long at others.”
To make matters worse, he says farmers have had a tendency to order water in excess of their actual needs in order to compensate for this level of uncertainty. Farmers often feel compelled to take water at less-than-optimal times agriculturally, just because they fear it may not be available later.
Burt explains that water requested in excess of need ends up being wasted, discharged from the canals through spill gates into nearby creeks. In addition to representing an unnecessary financial expense to the growers he adds that, “Dumping water that has traveled 300 miles into a creek also comes with huge energy costs as well.”
As a practical matter, Burt says modern water-saving irrigation techniques, particularly drip irrigation, require a continuous and consistent water supply in order to function optimally. “In order for farmers to effectively manage their water use, they must have water available at the times they need it and at the flow that they need,” he adds.
What farmers needed was water on demand, but, for a 100-mile-long canal system, that was no simple proposition, prompting the managers at CCID to turn to Burt for advice on this and a range of related operational issues.
And ITRC was prepared to help. With its staff of 14 full-time irrigation experts supplemented by 35 students, it operates as a high-powered consulting firm, “with specialized expertise in irrigation that would not be found in your normal engineering firm,” says Burt. “When it comes to automating long canal systems, we’re the only game in town.”
In a Day’s Work
The job of controlling CCID’s complex network of canals falls to CCID’s own staff of 16 canal operators working under the supervision of a water master. In addition to controlling the distribution of water to the various tributaries, crews record measurements at key points in the system to ensure that flows match the delivery capacity in the network and to allocate resources for future deliveries.
Operators also held the responsibility for manually entering the settings on the canal’s gates and weirs to direct water to the
appropriate tributaries and satisfy farmer requests. The water master’s long experience with the local farmers and their customary practices, weather patterns, and the idiosyncrasies of the canal system was key to smooth service. However, even with an experienced water master, Robert Stoddard—of the firm Boyle Engineering, which consulted on the modernization project—says, “managing the canal was an art.”
In order to attain the project’s efficiency goals, the complex knowledge base of the water master would need to be replicated by a computerized system and placed under automated control.
Using data gathered from maps, service records, and other information provided by CCID, Burt’s team at ITRC produced a computerized simulation of the canal system. Burt says the team also developed simulation exercises to test a modernized version of their virtual canal under various conditions.
“We modeled the entire canal at one-second intervals while putting different characteristics into the controllers,” he says, adding that these computerized simulation efforts continued adjusting and tweaking the parameters of the model until the team had achieved a satisfactory level of correlation with the behavior of the real-world canal.
“We were able to get 90% of the results we wanted through a theoretical approach,” continues Burt. These results, “though quite good for a modeling exercise,” still needed to be supplemented with measures to cover the 10% discrepancy. However, according to Burt, even unexplained discrepancies could be accommodated in the model through “heuristic adjustments to the algorithms,” which he says amounted to the introduction of “a few rules of thumb,” into the formulae.
The algorithms derived through the simulation exercises were provided to project partner Sierra Controls Systems to be integrated into the instructions for programmable logic controllers (PLC). The PLCs, in turn, would be housed within each of the canal’s modernized check structures, and linked to a Supervisory Control And Data Acquisition (SCADA) system, which would direct the opening and closing of each individual canal gate along the system.
With the PLCs installed, and with each gate operating independently, the entire system would function in a coordinated fashion, increasing the efficiency of water delivery.
Faster Than Gravity
Jerry Kelley, president of Sierra Controls Systems, whose firm provided systems integration for the project, says he was somewhat surprised to discover how level the terrain lay through which the canals flowed.
“The natural lay of the land drops only five feet over the course of 30 miles,” he states. As a consequence he says, “the velocity of the flow is very slow,” and he likens CCID’s two canals to “two, long skinny lakes.”
But, Burt says the solution for CCID lay not in finding a way to move the water faster, but in cutting the distance it had to travel. It decided to divide the canal in half, incorporating a regulating reservoir roughly at its midpoint, which has the capacity to store a one-day supply of water within reach of the fields at the far end of the system.
The upper half of the canal draws its water directly from the Mendota Pool surpluses, from that end flow into the regulating reservoir at the canal system’s mid-point. On the upper half of the canal where the demand was greatest, the original management practice of upstream level control was maintained. However, downstream of the regulating reservoir, new procedures were adopted to convert operations to a new management paradigm based on downstream level control. Kelley says that, under this method of control, sensors placed in the pools downstream of the corresponding gates were used to detect water levels and signal gate movements.
On the lower end of the canal, when the required flow rates are achieved, the gates would shut and excess flows would be backed into the new auxiliary reservoir. Through this method of control, Burt says spills could be avoided, and the water recaptured and stored could be made available for later use, thereby setting the groundwork for flexible service.
“In theory, you could operate the system by looking at how the reservoir is behaving,” says Stoddard.
Burt amplifies this point. “With flow control at the head of the canal, if we look at the reservoir and it’s a little high, we won’t take quite so much,” he says.
|Photo: Central California Irrigation District|
Downstream of the regulating reservoir, new procedures were adopted based on level control.
Using this system, the canal does in fact “act like a pipeline.”
As an added benefit to the project, Burt says the auxiliary reservoir approach represented “the least-expensive technology that would work for that district.”
At various intervals, CCID’s canals had been equipped with wooden flashboard check structures, segmenting the flow to allow sufficient head to build behind the structure to facilitate
While that infrastructure was still operational at the outset of CCID’s improvement project, modern check structures would offer CCID management more precise control. Langemann radial gates provided the best match for CCID’s operational requirements.
Installing these new check structures, however, provided a bit of a logistical challenge. According to Stoddard, irrigation canals are typically allowed to run dry during a well-defined off-season after the harvest, providing an ideal opportunity to perform maintenance and upgrades in the trench. In contrast, however, CCID’s canal system must remain fully charged throughout the year, providing no such fallow period. In addition to supplying water for agricultural purposes, the CCID canal system is mandated to provide water year-round to support environmental uses such as natural habitat and fisheries in the region.
This year-round demand necessitated a leapfrog approach to the replacement of the antiquated control structures. As the project moved along, the original flashboard gates were maintained in continuous operation while alternative locations some distance away were selected for their replacements, says Stoddard.
To accomplish this, Stoddard says one of the contracts in the complex construction project was specifically dedicated to dewatering work sites and establishing temporary water conveyances to bypass construction and, thereby, maintain scheduled environmental water deliveries.
Supplying power to CCID’s improved infrastructure also presented a challenge, particularly in remote parts of the agricultural districts. Burt says over the 110-mile course of the canals, a number of control structures would be situated in areas lacking access to primary power.
Kelley says actuator motors, sensors, communications systems, and PLCs at these remote locations had to be outfitted to operate on battery power, with onsite solar collectors providing the energy. However, according to Kelley, to economize on power, the actuators on these battery-powered gates have to make adjustments very gradually.
Acclimating to the New System
Once installed, the control structures were put through their paces during a phased implementation process. Burt says this shakeout period provided ITRC engineers with the opportunity to test the PLC control algorithms against actual conditions in the field, fine-tuning the algorithms in “an ongoing process of refinement.”
|Photo: Central California Irrigation District|
WIth PLCs located on various check structures relaying information on gate status, and sensors in the upstream and downstream pools, headquarters receives operational updates every 60 seconds.
He adds that CCID took precautions against this by building a high degree of redundancy into the system. “If you have a single sensor at a point, should the sensor malfunction there’s no way to check the accuracy of that data, so we double everything,” says Burt. “We measure water level with two sensors.”
Stoddard says, however, there is another important detail that must not be overlooked—staffing. It was CCID’s intention from the outset to retain its original staff of operators, but the management of the modernized canal would require new procedures. Stoddard says the phased implementation period was also designed to give operators time to acclimate to the new system. “It takes an entirely new skill set to operate and interpret the data through the SCADA system,” he says. “Operators needed time to learn to trust the new system and the information it was giving them.”
He adds that it was important to bring the old employees along as the system developed. “This is all a fairly new technology,” says Stoddard. “We worked in tandem with Dr. Burt and his team and learned quite a bit, not only about good measurement systems, but also the importance of building redundancy into the system. The important thing is to move in an orderly fashion and decide which components will be changed first, involve operators, and give them a good understanding of what’s going on.”
By 2007, the automation project was complete and the entire canal system was under SCADA control. The radio communications network installed by Sierra Controls keeps everything coordinated—ping ponging data between stations. With PLCs located on the various check structures relaying information on gate status, and sensors in the upstream and downstream pools relaying water level data, headquarters receives operational updates every 60 seconds—a great advantage over earlier procedures.
“In the past, when there was a problem they’d have to call someone on radio and have them drive out to the site to figure out what was going on,” says Stoddard. “Now it’s done automatically by radio and the water master can see it on his computer screen.”
Kelley agrees. “Remote control is a true time saver,” he says. “In inclement weather the canal banks can get slippery and muddy. With the new system, all control is back in the office, and with the computer calling each site in succession, all the information is less than one-minute old.”
He says the result provides “good control of water with a lot less travel to each site.”
Nonetheless, Stoddard cautions that irrigation canal modernization and automation should not be focused on cutting labor costs.
“A lot of people think, ‘We’ll just automate and we won’t need canal operators anymore,’” he comments.
But, he says, the opposite is true.
As a result of automation, “We [CCID] would need more highly trained personnel,” says Stoddard. “This type of project requires significant expense not only for capital improvements, but also for operators and training. However, the overall savings in water efficiency outweigh the investment in the long term.”
Rating: 0.00 / 5.00
For additional information on this Earthworm News article, please contact:
Source: David C. Richardson
Content Tags: earthworm news •
Return to Green Industry Jobs, Articles Search