By Dave Bennett
Delivering water from foothills to farmland is like pulling a string of freight cars with a vintage steam engine: The system works, but there's room for improvement. A water supplier in California's almond-growing Central Valley, however, has begun researching a way to significantly cut consumption.
The South San Joaquin Irrigation District (SSJID) in Manteca serves a sizeable community in a state and region where water access and conservancy are a constant concern. Until this year, water was delivered just as it had been for more than a century: through 400 miles of gravity-based canals and pipelines. Farmers drew from the network of laterals at scheduled times via flood irrigation or private pumps used for sprinkler or drip systems.
While the system works well for flood irrigation, the combination of flood and sprinkler usage on a single system becomes problematic as the number of sprinkler users increases. Having both types of customers on the same lateral creates significant flow challenges, with flood users typically receiving less than they need and the sprinkler/ drip irrigators often unable to use the district's surface water on a reliable schedule. Trying to balance the flows often causes spills to the drain. In addition, the district's fixed, 10-day delivery schedule doesn't offer the flexibility that increasingly scientific irrigation methods require. As a result, some customers didn't buy water from the district, opting instead to draw from their private wells.
Despite significant water loss and operational inefficiencies, though, gravity-based irrigation systems are quite common. About half of all farms in 17 Western states rely on them, according to the U.S. Department of Agriculture.
The district had historically subsidized expenditures with revenues from upstream power generation. While this kept water rates at $24/acre, it also provided no incentive to improve efficiency.
That changed in 2009. A growing population and competing demands for limited resources prompted California to pass the Water Conservation Act. In addition to a 20% reduction in per-capita urban consumption by 2020, the law requires agricultural suppliers to “implement efficient water management practices” and volumetric pricing by next year. With a statewide assessment of water use under way, the SSJID Board of Directors realized the issue posed a potential threat and approved an upgrade.
They commissioned Stantec Consulting as a partner in developing an irrigation program that could improve delivery efficiency while fully maintaining — and potentially improving — service. A portion of one of the district's nine divisions — 3,800 acres in Division 9 — was chosen as the site for building, testing, and optimizing a pilot project before replicating similar strategies districtwide. Over the three-year design period, Stantec and district representatives met extensively with all of the division's farmers to discuss their vision for the system, which included the following fundamental capabilities:
Pressurization — pumping water from a 56-acre-foot pond to individual farms through 19 miles of pressurized pipeline
- Calculated use — letting farmers choose the time, volume, and pressure of deliveries
- Automated/mobile access — developing a Web-based tool that allows farmers to schedule deliveries from a computer, smartphone, or iPad based on current and past weather forecasts, previous water usage and historical evapotranspiration rates, and orchard moisture sensors.