Submitted to: Encyclopedia of Water Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 1, 2003
Publication Date: July 1, 2003
Citation: Clemmens, A.J., Replogle, J.A. 2003. Irrigation metering. Encyclopedia of Water Science. p. 495-497. Interpretive Summary: Water supplies in the Western United States are not sufficient to meet current water demands, especially when considering water needed for environmental purposes. Irrigation accounts for a majority of water demand in the United States. Thus, irrigated agriculture is under pressure to measure and account for their water diversion more accurately. This paper describes methods for measuring irrigation water flow for nontechnical audiences. These results should be of use to those interested in water issues and the general public. Ultimately better management of irrigation water supplies will conserve water and benefit the environment.
Technical Abstract: The measurement of applied irrigation water is one of the major links in efforts to achieve effective water management worldwide. Measurement of flow for irrigation differs from most municipal and industrial water metering requirements because the water is spread over very large areas. This usually results in the need to measure both very large flows in canals near water supply sources and small flows spread over very large areas, perhaps in small trickle irrigation lines near the points of use. Irrigation was often done with waters that were not be needed by other uses, although competition by these other uses is increasing, causing much controversy in water use planning, policy, and development; therefore enhancing the need for accurate flow metering. Traditionally, flow meters have been classified according to the physical principle or property exploited, such as those related to sound, magnetism, electricity, chemical reactions, mixing, and volume, mass and energy relations (1). The device that exploits these properties to interact with the water is called the primary element, and produces an indication that can be detected with a secondary element for the user to observe, or otherwise use. This classification of meters according to exploited properties can be broadly grouped into flow-rate meters or quantity meters, according to the effect that is first observable. For example, a weir is a flow rate meter, and a bucket is a simple quantity meter. Not all meters are currently practical for use in irrigated agriculture. Major restrictions to irrigation applications are often the lack of electric power at the metering site, capital cost, and poor maintenance support. Thus, practical irrigation metering emphasizes low cost, reasonable accuracy, and simplicity and the ability to meter waters with high sediment and/or trash loads. Meters that meet these criteria for the irrigation setting are discussed below. A wide variety of meters are discussed in more detail in (2) and (3).