by Necmi Sanli, Energy Systems Engineering
December 17, 2011

Lindmore Irrigation District uses Ethernet radios to improve SCADA communications system and pumping efficiency.

In many areas of the world, agriculture depends on irrigation. This is particularly true in Central California where increased demand and limited water supply creates many challenges for irrigation districts.

Because of their importance to the agriculture base, investments in maintaining and upgrading irrigation systems must have a high priority. Automation is necessarily a part of that investment because it enables water districts to conserve water and power and to lower labor costs and reduce overhead while ensuring accurate billing.

An electrical engineering firm is working with the Lindmore Irrigation District in Lindsay, Calif., to upgrade its SCADA network. As part of this upgrade Phoenix Contact was chosen to provide Wireless Ethernet (TWE) radios, antennas, and power supplies (Figure 1).

Figure 1. A Phoenix Contact radio and power supply mounted in a control cabinet

Irrigation Challenges

The Lindmore Irrigation District is located in the east central portion of California's San Joaquin Valley. It receives its water from the Friant-Kern Canal, a 152-mile Central Valley Project aqueduct managed by the U.S. Bureau of Reclamation in Central California.

The district serves the communities of Lindsay and Strathmore, Calif., as well as around 1,200 agricultural customers that grow citrus, olives and almonds in a 100 square-mile (10-mile x 10-mile) area. It also provides supplemental irrigation capacity to Fresno, Tulare and Kern counties.

Completed in 1951, the Friant-Kern Canal begins at Millerton Lake, a reservoir on the San Joaquin River north of Fresno. It flows south along the eastern edge of the San Joaquin Valley, ending at the Kern River near Bakersfield. The canal provides water at 5,000 cubic feet per second (cfs) at its source, gradually decreasing to 2,000 cfs at the Kern River.

On the west side of the district, water is delivered to about 500 farmers on more than 26,000 acres. Water flows from east to west from the canal through 18- to 22-inch main pipelines. Pipes connected to the main pipelines run north to south to supply water to the farmers.

The 10-mile by 10-mile area is a very large area to cover, but pumping is not required on the west side of the canal because these pipelines are gravity fed.

The three gravity-fed bilateral pipelines (called “avenues”) are approximately five miles apart. Each of the first two is about 10 miles long. The third is about eight miles long. These bilateral pipelines transport the water from the canal to the farmers.

Rise tubes or pipes located every 2 to 5 miles along the bilateral pipelines maintain head pressure. Specifically, a programmable logic controller (PLC) that is part of the district's SCADA system maintains the head pressure by operating gate valves at the rise tubes. Before the PLCs were installed, operators had to drive to each rise tube to manually open and close the gate valves.

However, locations on the east side of the canal need pumps to push the water to higher elevations. A pumping plant operates several pumps with motors from 25 to 60 horsepower—some with variable frequency drives (VFDs) and some without. Water delivery rates range from 1.7 cfs to 3.3 cfs. The system was largely manually controlled, which left considerable room for improvement.

Manual to Automatic Control Conversion

The primary objective of the pumping plant is to maintain reservoir level and flow demand (Figure 2).

Figure 2.  Irrigation pumps deliver water to customers in the higher elevations to the east of the canal. 

When farmers call with their water requirements, district operators select the number of pumps to operate. Each pump has a selectable setpoint at the reservoir level. Once the reservoir level reaches its setpoint, the pumps stop. Head pressure at the reservoir maintains the line pressure.

In the past, the district relied on manual metering to provide water to its customers. When a customer needed water, a technician had to drive to the customer's site and manually open a valve. This process provided almost no flow rate or water volume data. The only way to measure how much water was delivered was to note how long the valve was open.

Not knowing exactly how much water each customer received made billing difficult and potentially inaccurate, not to mention the wasting of resources. Deviation between the amount of water actually provided and the estimated amounts could vary from 30 to 40 percent.

The district estimated water volume according to motor horsepower, pump efficiency and elevation. If the district operators knew the field size and flow, they just needed to determine how many pumps they needed to operate. For example, if they needed a flow rate of 6.6 cfs, they turned on three pumps and billed accordingly.

The State of California maintains official flow measurements at the canal water connection points. The state allowed the Lindmore Irrigation District to connect to its meters. The water measurement deviations were based on the difference between the state's measurements and the district's estimates.

Before the upgrades, the district's water delivery and measurement system was not accurate or efficient. Now, the district measures and monitors actual water use. The operators record exactly how much water flows and where it goes, and the database keeps track of the water use and billing.