Flood Irrigation in the Desert Southwest
The first dam on the Colorado River was Laguna Dam built in 1905, seven years before Arizona became a state, followed by 14 more dams in 61 years to completely control the flow. Similar water management projects were made on all rivers across the state, providing access to local communities. Complex canal systems were built over time, with a major public works project occurring post World War II. The canal systems of Arizona were specifically designed to deliver high flows of river water to the field to support flood irrigation, which resulted in a greening of the desert and vast improvements to agriculture.
There are many reasons why basin-flood irrigation remains the cheapest and easiest form of irrigation possible in desert agriculture to this day, with dirt borders raised around a field to hold in a steady flow of water that fills the basin. The ‘flatwater’ practice not only irrigates crops, but also recharges soil nutrition and improves soil health by leaching concentrated salts that build up at the soil surface. Furrow-flood irrigation is the next iteration of surface irrigation, with crops grown on raised beds and water directed down the field in low furrows between raised beds. The water fills the furrow and is slowly absorbed into the sides of the raised bed, wetting the plant and pushing soil salts laterally. Furrow-flood has the added benefits of reducing the total water used compared to basin-flood, and limiting crop damage from overwatering.
As cheap and reliable as flood irrigation may be, often it is not the most efficient use of water, with water evaporating or soaking into the soil below the rootzone, taking mobile fertility with it. More modern irrigation solutions designed to increase irrigation efficiency exist, but are often expensive to purchase and maintain.
On-Farm Water Irrigation Efficiency Project
With the help of the Western Growers Association and individual farmers, the University of Arizona grew a $30 million grant into a $62 million program that is working directly with farmers to assist them in converting from flood-irrigation to more efficient systems, which has currently saved over 36,000 water acre-feet (12times the size of Tempe Town Lake).
Seven months ago, in February 2023, the UArizona Cooperative Extension received a $30 million grant from the Arizona Governor’s Office to research how to reduce on-farm water usage while maintaining soil health and crop yields. A total of $23millionwasset aside to directly support Arizona farmers by reimbursing growers and farmers up to $1,500 per acre to change to a more efficient watering system. The UArizona Water Irrigation Efficiency Program will reimburse the growers using flood-irrigation, or vendors for creating 20% or more water efficiency savings. Western Growers Association was a vital outreach organization, hosting two in-depth seminars for growers and coordinating informational meetings and outreach to vendors, irrigation districts, and growers. Overall, the educational campaign reached more than 1,500 people, including over 100 on-farm site visits by Cooperative Extension faculty and staff.
“The Cooperative Extension staff made the application very simple to work through and were quick to respond to us throughout the process. The application website that we applied through made it simple to upload all pertinent documents in one location and made it simple to submit multiple applications,” said Mike Clements, Ranch Supervisor for Topflavor Farms in Yuma. “In the short term, we were able to acquire and implement several new irrigation systems in a short amount of time and put these systems into use immediately. We received notice that our grants were approved in mid-June and were able to have the first system installed and operational for our first wet date in early September. The long-term impact is going to be hitting our goal of reducing our water usage by 20% year-over-year.” Topflavor is expecting to save 1-1.2 acre-feet over 190 acres, nearly 60 million gallons in total.
The Barkley Company of Arizona opted to utilize the program on a 200-plusacre farm in the Welton-Mohawk Valley. Located toward the terminus of the canal, they have opted for a variety of new irrigation systems. “This was an opportunity to be more efficient with our water now and plan for the future, especially if there are changes in availability of water,” said Hank Auza, General Manager of the Barkley Companies. The improvements include a gravity-fed retention pond, improved pressurized drip irrigation, and electronic gates.
Between February and August 2023, the Water Irrigation Efficiency Board approved62applicationsforapplicants in 11 of Arizona’s 15 counties. These projects will help our state conserve 36,418 water acre-feet (WAF) annually, equal to over 12 times the size of Tempe Town Lake. Additionally, farmers invested their own funds matching the $23 million in public sector money with $16,515,088 in private sector money. Ultimately, over 42% of the water savings program funding came directly from farmers. Because of support from farmers and growers, the public cost per water acre-foot conserved was a mere $631, approximately one-fifth of the cost of desalination.
Conventional Alternatives to Flood Irrigation
A movement toward agricultural water conservation was made in the 1970s with sprinkler technology used to cool and moisten instead of soak. Vegetable production regions adopted solid-set sprinkler irrigation powered by a mobile diesel pump and modular 30-footsections of aluminum or PVC pipes. Circular center-pivot sprinklers for open land, or linear-move sprinklers for square fields, were widely adopted in row or field crops across the state. Drip irrigation, an even more water-wise choice, became commercially available in the early 1980s, with the greatest success stories hailing from cotton production, with some farms reporting decades of continuous use without changing the drip-line.
Emerging Irrigation Technologies
As water becomes scarce, the demand for resource conservation has increased, driving irrigation efficiency innovation and on-farm adoption. Emerging technologies include: canal automation, with gates that meter water with more precision for greater control; gravity-drip irrigation, pump-less drip; moisture meters, used to trigger irrigation events; and automated micro-jet sprinklers for orchard production. Additionally, the UArizona Cooperative Extension service utilized UArizona Water Irrigation Efficiency Program funding to develop and evaluate a more efficient method of basin-flood irrigation.
In winter vegetable production regions, such as Yuma, solid-set sprinklers are commonly used to germinate seed and irrigate some crops to completion, so the pipe is readily available and in use. Sprinklers are some of the most water-efficient systems available but cannot be used in spring rotational crops of wheat or sudan grass, after emergence, due to kernel damage and plant height. Traditionally, these crops are basin-flood irrigated, undermining winter water savings of sprinkler pipe. The UArizona Cooperative Extension solid-set flood irrigation system replaces the interchangeable sprinkler heads on standard solid-set sprinkler irrigation pipe with high-flow, pressure-regulated ‘bubbler heads’, used to basin-flood irrigate with more precision. Solid-set flood irrigation spreads water out evenly across the field from heads located every 30feet, fixing the basin-flood irrigation problem of oversaturation near the canal gate where water is introduced into the field and undersaturation occurs at the opposite end of the field. Pipes remain in the field during crop growth and removed before harvest by pulling out of the field with a pipe-pulling machine or drug out with a tractor and a chain. In general, flood irrigation is not as efficient as other systems but is still the only method that is used to mobilize and leach toxic salt concentrations, which may be an added value of this system.
Conclusion
Water conservation advancements will continue to grow as the essential resource of water becomes more scarce. It is expensive to conserve water, but through mindful use it will be available for longer. The UArizona Water Irrigation Efficiency Program is in place to assist growers with the cost of water savings, and UArizona Cooperative Extension will continue to assist growers trying out these new technologies, while providing optimization tips and operation and maintenance advice. Through grower flexibility, commercial innovation, and University of Arizona support, our civilization will continue to thrive in Arizona and provide the nation with healthy food for their plates.
With the support of WG and other agricultural advocacy organizations during the 2023 legislative session, Arizona allocated an additional $15.2 million to fund the program next year. A total of $14 million will be set aside to directly support farmers, and $1.2 million will be used for irrigation and crop research. The Arizona Cooperative Extension’s goal is to support Arizona growers with research, education, and programming. Next year, the UArizona On-Farm Water Irrigation Team will continue to partner with growers and work to conserve even more water for Arizona. Investing in Arizona’s growers is the most cost-effective way to save water.
