Irrigation

Central’s first deliveries of water to irrigators took place in 1941 and began in earnest the following year with deliveries to more than 44,000 acres. Over the next 35 years, the number of irrigated acres grew to more than 123,000 (the number of irrigated acres has remained stable at about 112,000 acres since 1984) and the canal system operated as designed with only minor changes or improvements, such as replacement of wooden turnouts with concrete structures, and the construction of the E67 Canal in the mid-1950s.

Advances in technology and a better understanding of hydrogeology would bring improvements, starting with planning and design for the E65 Rehabilitation Project in 1969. Small project loans from the U.S. Bureau of Reclamation — the first obtained in 1975 and the second in 1980 – allowed Central to rehabilitate and modernize its two main irrigation systems: the E65 Canal, which serves almost 43,000 acres in the Bertrand-Loomis area; and the Phelps Canal, which serves almost 60,000 acres from northwest of Holdrege to north of Minden.

The E65 project consisted of enlargement of most of the E65 Main Canal, new control structures, the addition of Elwood Reservoir and installation of supervisory control equipment on the principal operating structures.

Elwood Reservoir, located just south of Johnson Lake, is filled during the non-irrigation season by diverting water from the Supply Canal into the E65 Canal. The water is pumped into the reservoir at the Carl T. Curtis Pump Station. Each year, approximately 24,715 acre-feet are pumped into the reservoir, which has a capacity of more than 40,000 acre-feet. The water is then allowed to flow back out of the reservoir during the irrigation season for delivery to irrigation customers. The releases augment the E56 Canal’s diversion capacity of approximately 365 cubic feet per second.

The project also improved service to E65 customers by increasing deliveries from 1 acre-foot per acre per season to 1-1/2 acre-feet per acre per season and switched deliveries from three-week rotations to two-week rotations.

The Phelps loan provided funds to rehabilitate 64 miles of the Phelps Main Canal, some lateral enlargements, plus additions and modifications to major control structures. The Phelps Canal is Central’s largest irrigation canal with a capacity of 1,300 cubic feet per second. More than half of the Phelps system’s 250 miles of canals and laterals were replaced, rehabilitated or improved by 1986 and additional improvements have been made on an annual basis since that time.

The E67 Canal, which serves more than 5,000 acres southeast of Johnson Lake, was added to the system in 1954 at the request of area farmers who experienced difficulty in procuring adequate supplies of groundwater. In 2001, Central began another ambitious improvement project on the E67 Canal. Completed in time for the 2003 irrigation season, the project replaced most of the canal system’s open laterals with 18 miles of buried pipeline and 2.8 miles of membrane lined canal.

The project provided a two-week delivery rotation for irrigation customers, rather than the three-week rotation that had been in place since the canal went into service. Transportation losses (seepage and evaporation) were largely eliminated, resulting in an annual reduction in diversions to the canal system by 45 to 50 percent.

Central continues annual maintenance and improvement activities on its canal systems. Several small and/or inefficient canals have been abandoned or replaced with pipelines. Membrane lining has been added in areas where seepage losses were unacceptably high.

Central also provides irrigation water to about 6,000 acres served directly from the Supply Canal as it passes through Lincoln and Dawson counties to the headgates of the three irrigation canals in northeast Gosper County.

An important part of the rehabilitation projects was the attention given to designing, incorporating and improving the “conjunctive use” aspect of Central’s system.

Within the context of Central’s system, conjunctive use is the recognition of the hydrologic relationship between surface water irrigation and groundwater resources and the effective, efficient use and management of both resources to produce sustainable social, economic and environmental benefits.

During the planning stages for the E65 rehabilitation project, computer groundwater modeling studies of the system resulted in a design that provides recharge where groundwater development (irrigation wells) is heavy and a lined system, or pipelines, where irrigation comes mainly from the surface water system. The result has been a generally stable water table beneath and adjacent to Central’s service area.

Central’s efforts marked the first time in Nebraska that an irrigation system was designed to address the water supply and the needs of both surface and groundwater irrigators. Central monitors a system of 137 observation wells throughout the service area, enabling the District to compile the necessary data for continued evaluation of groundwater levels.

Data from the U.S. Geological Survey and the Conservation and Survey Division of the University of Nebraska-Lincoln show that the water table beneath Central’s service area has risen since the system went into operation in 1941 by 10 feet to more than 50 feet. Similar data from counties just outside Central’s service area show just the opposite – declines in the groundwater table of five to more than 30 feet over the last 60 years.

Central has several types of state water rights. Irrigation water rights have been obtained for the land served by Central’s distribution system. These water rights remain with the land regardless of its ownership as long as water is applied to the land. Irrigation water rights for each parcel fall into two categories: natural flow and storage use rights.

Natural flow is diverted from the base flow of the river and these types of water rights are administered by the Nebraska Department of Natural Resources on a “first-in-time, first-in-right” principle. As the natural flow of the river diminishes, junior water rights are shut down so more senior, or older, water rights can continue to receive water. Central’s earliest water rights were obtained in 1934, but are still junior to most other Platte River water rights, many of which date back to the 19th century.

The majority of Central’s diversions for irrigation are storage water released from Lake McConaughy. Central has a water right to store 2 million acre-feet annually behind Kingsley Dam.

Several irrigation projects that depend primarily on natural flow water rights contract with Central or other irrigation projects for supplemental water; that is, storage water that can be delivered when natural flow is unavailable or available in insufficient quantities.

Another type of water Central holds is a permit to divert water for the production of hydroelectric generation at its four hydroelectric plants.

Installation of supervisory control capability for Central’s E65 and Phelps irrigation canals started in 1977 and was completed in 1985. The main structures on both canals are monitored and controlled at Holdrege, Bertrand or Gothenburg, depending upon circumstances and the time of day.

A canal system can be placed in an “automatic mode” that allows the computer to maintain canal levels by operating the control gates. This minimizes the effects of sudden rainstorms or use changes and reduces the adjustments that canal patrolmen (also known as irrigation service specialists or ISS) must make over the course of a day. It also allows timelier adjustment of canal flows and reduces the number of miles ISS must travel within the irrigated area.

Automated structures have electrically operated gates with position transmitters, upstream and downstream meters that indicate canal elevation above and below the structures, and remote terminal units (RTUs) that link the equipment together. Data reports from the RTUs are sent via microwave signal to computers that either operate the system or provide information to a control operator who can enter the necessary commands.

Management of water resources is an important part of Central’s operations. To manage the system properly, it is imperative that accurate measurements are taken and that thorough records are compiled. Such practices enable Central to evaluate and adjust its operations accordingly.

Each customer’s turnout is fitted with a water meter or is measured by an ISS. Records of deliveries are kept down to the tenth of an inch.

Central has been active in water conservation efforts for many years and has gone to great lengths to improve the efficiency of its delivery system. Practices include conversion of turnouts to pipe outlets fitted with flow meters; encouraging the use of soil moisture blocks and soil probes to measure soil moisture; digging reuse pits for landowners throughout the irrigated area; improvements in the supervisory control system to increase the timeliness of deliveries; creating the position of conservation director to work directly with irrigation customers on on-farm systems; cooperation with federal and state natural resources agencies; and adoption of conservation policies that encourage and reward irrigation customers for adopting conservation measures or practices.

Once the water is delivered to the farm, most irrigators use pivots to apply the water to the field.  More than 700 pivots were taking water directly from canals, laterals and pipelines, accounting for about two-thirds of the acres receiving delivery service from Central.  The balance of the acres are served with gated pipe, although there are now about 20 sub-surface drip irrigation applications delivering water to crops.