Improving Irrigation Operations to Restore In-Stream Flows
CLIFFORD A. PUGH, Hydraulic Engineer
Bureau of Reclamation
Hydraulic Investigations and Laboratory Services Group
P. O. Box 25007, Mail Code 86-68460
Denver, CO 80225
The American West has been progressively developed for farming over the past 100 years. As farmers settled the arid West, it became evident that rainfall didn't always come at the right time, the right place, or in the amounts needed for homesteaders to thrive and prosper. In 1902, the Bureau of Reclamation was created to help alleviate this problem by storing snowmelt and other water for later use and to create conveyance systems to move water to lands where it was needed.
Canals and other water delivery systems are a big part of the total water management picture, yet most irrigation canal systems are still operated as they were 70 years ago. Modern methods of operating irrigation canal systems can significantly improve water use efficiency and make water available for other purposes, but implementation of these methods is not yet widespread on older projects.
This paper will discuss modern methods of canal operation and control that making existing projects more efficient, thereby making water available for environmental needs and other uses.
In-Stream Flows, efficiency, conservation, operating canal systems, irrigation, environmental impacts, environmental restoration, fish passage
A typical irrigation system in the Western United States diverts water from a river at a diversion dam. The water is then conveyed through a "highline canal," along the contours of the land, roughly parallel to the natural stream course. The water is delivered by gravity from the highline canal and a network of other lateral canals to the farms . Excess water, sometimes termed "administrative spill," is also diverted and conveyed through the canal system to assure that all of the farms receive their share of the water. The excess flow is returned to the natural stream-course, many kilometers downstream from the diversion, through drains and wasteways. In some cases the highline canal may cross basin boundaries, producing drainage to a different stream.
Passage of the Endangered Species Act of 1973 and other environmental restoration legislation has increased emphasis on restoring in-stream flows throughout American river systems. Diversion dams are also being modified to enable fish passage, thereby restoring access for the fish to essential habitat. The fish ladders require an adequate attraction and operational flow to make them effective. This requirement adds to the need for additional flow passing the diversion dams.
Figure 1. Vicinity map, Grand Valley Project
Improved operation of canals has potential to provide significant additional flows without developing additional storage. Historically, canal operations have been handled by the Canal District receiving advance water orders. Diversions are made , many hours in advance, at the head of the canal to meet these orders. Administrative spill is added to assure that farmers throughout the system receive water that they are entitled to. Modern methods of operating and controlling the canal system can provide the flexibility needed in the primary open-channel conveyance system to allow the farmers more freedom to turn the water on and off as needed, while reducing the need for administrative spill. These improvements have the potential to yield both agricultural benefits and environmental benefits. Increased delivery flexibility and dependability will benefit farmers and canal operators while better system management reduces water waste, maintenance costs, and environmental impacts. Crops will receive the correct amount of water at the correct time to optimize production. New piped deliveries for laterals and turnouts are helping to provide the individual farmers with the flexibility needed; however, the control of the main canal system is more challenging. The canals have a maximum flow capacity that they can convey at any given time. Therefore, deliveries must be rotated on a schedule during peak demands to give everyone their turn.
Grand Valley Project-
The Grand Valley Project, near Grand Junction Colorado (figures 1 and 2) demonstrates the problems encountered by canal operators throughout the West, and the possibilities for improvement by using modern canal operation methods.
Grand Valley is in west-central Colorado in the Colorado River Basin. Water is furnished to about 16,200 hectares of land along the Colorado River in the vicinity of Grand Junction, Colorado. The project works include a diversion dam, a powerplant, two pumping plants, two canal systems totaling 145 km, 267 km of laterals, and 180 km of drains. Water for project use is diverted into the Government High Line Canal at Grand Valley Diversion Dam, about 37 km northeast of Grand Junction. About 7.4 km below the main diversion, water for the Orchard Mesa Division is diverted from the canal. This water passes through the Orchard Mesa Siphon across the Colorado River, through the Orchard Mesa Power Canal to the Grand Valley Powerplant, or to the Orchard Mesa
Figure 2. Grand Valley Irrigation Project near Grand Junction Colorado.
Pumping Plant, where it is pumped into Orchard Mesa Canals No. 1 and 2 for distribution to water users. From the Orchard Mesa diversion, the Government High Line Canal continues westward, approximately paralleling the river, distributing water to laterals of the Garfield Gravity Division. Water also is furnished to 3,430 hectares in the Mesa County and Palisade Irrigation Districts which were served by private facilities prior to project construction. Water must be diverted well in advance to anticipate demands throughout this system.
Grand Valley Diversion Dam- The diversion dam is on the Colorado River about 13 km northeast of Palisade, Colorado. This concrete weir is 4.3 meters high. Flow over its 116 m crest is controlled by six roller gates. These gates were the first of their type designed in the United States.
Government High Line Canal System- The canal is on the west and north side of the river and extends from the Grand Valley Diversion Dam south and west a distance of 88 km. It has a diversion capacity of 50 cubic meters per second, which includes 23 cubic meters per second for the Orchard Mesa Power Canal. The remaining flows are distributed through the Government High Line Canal and Price-Stub Pumping Plant. The distribution system for the Garfield Gravity Division consists of 267 km of laterals. The drainage system consists of 3.2 km of closed drains and 178 km of deep open drains.
The Grand Valley Project is typical of early Reclamation irrigation projects. Typically, deliveries are anticipated by farmers turning in prior water orders-- "supply oriented operation." This leaves little chance for the farmers to apply modern on-farm techniques to improve crop yields while reducing water usage. If the farmers turn off their water before their scheduled delivery time is over, the excess water will typically be passed through a wasteway.
Figure 3 compares crop evapotranspiration (ET) vs. farm demand vs. flow diverted from the Colorado River for a typical irrigation season from March through November. The area in white under the shaded areas is the estimated crop ET. Slightly more water than this is needed to flush salts from the root zone. However, this chart indicates that there are significant water conservation possibilities both within the on-farm irrigation demands (the area in black) and the administrative spill ( the hatched area.) Reclamation is currently working with the Grand Valley Water Users Association to implement methods to bring these curves closer together. The obvious solution is to place the entire delivery system in pressurized pipe, similar to an urban water supply system. However, this approach would be extremely expensive and is cost prohibitive. For most of the older irrigation systems a comprehensive Supervisory Control and Data Acquisition (SCADA) system is also cost prohibitive.
The recommended approach is to implement telemetry and control along the canal on an incremental basis, with the canal operators working as part of the team to upgrade the system. The canal operators know, from years of experience, how their canal operates and can provide invaluable insight. Technical assistance and training on modern methods and new computer operated systems and equipment has also proven extremely successful to facilitate the transition to modern, more flexible canal systems.
Electronic monitoring and telemetry of information at various points throughout the canal system will facilitate operation of the canal system to make the flow deliveries to the farmers more "demand oriented." In the demand operation mode the monitoring system alerts the canal operator of changes in demand and appropriate changes are made at the check gates throughout the delivery system. Intermediate storage reservoirs in the canal system can help alleviate imbalances in the canal supply and demands; however, significant savings can be obtained by using telemetered information and the storage in the canal pools between check gates. Of course the flexibility in deliveries is reduced when the supply canals are operating near capacity, since the check gates are opened more and cannot supply additional flow if the demand increases further. During peak demand, rotation of deliveries may be necessary.
Figure 4. Flow measurement station at Indian Wash, north of Grand Junction.
Figure 5. Solar-powered data collection and telemetry station.
Figures 4 and 5 show a flow measurement and monitoring point midway through the Grand Valley Project. Figure 5 shows a low-cost microprocessor used to monitor flow at this key location on the Government Highline Canal, directly north of Grand Junction.
- Water systems automation technology plays a major role in the continuing effort to improve water project operations. Many improvements are now feasible because of recent advancements in data collection, communication, and control technologies. This technology can benefit most irrigation projects.
- Canals and other water delivery systems represent a big part of the total water management picture. Modern methods of operating irrigation canal systems can significantly improve water use efficiency and make water available for other purposes, but implementation of these methods is not yet widespread on older projects. The application of modern monitoring and control technology is one of the few "new" methods to increase agricultural water conservation. On many water projects, automation is the single option with the greatest potential for improvement in water system operations. Even a modest reduction in administrative spill can provide significant supplemental in-stream flows.
Water Power and Resources Service (United States Bureau of Reclamation,) "Project Data," Denver, 1981, U.S. Government Printing Office.
Norman, Bob, " GVIEP Water Conservation Study," January 1992.