SOME OBSERVATIONS ON IRRIGATION FLOW MEASUREMENTS AT THE END OF THE MILLENNIUM

Abstract

This article provides a brief historical look at the origins of flow metering in the last millennium, touching onsome of the developments we use today in openchannel and pipeline flows for irrigated agriculture. While the basic physicalprincipals recognized as useable for measuring flows have remained basically unchanged, the range and accuracy ofmonitoring these physical effects have been vastly improved by collateral developments in electronics and computertechnology. For example, the ultrasonic properties of a fluid medium have long been recognized, but only in the last decadehave the practical and inexpensive means to exploit these properties become available. Some of the newer developmentsduring the last quarter of the past century include longthroated flumes of many shapes for which the discharge ratings, orcalibrations, are determined by computer techniques. A recent extension to the computercalibrated flumes repertoireincludes the adjustablethroat flumes that aid in placement in earthen channels because they virtually eliminate concern forvertical elevation of the throat, which can be adjusted to accommodate ditch flow conditions after installation. Other recentdevelopments include: vortexshedding meters; ultrasonic flow meters, of both the Doppler type and transonic types; andsimplifications on construction and application of Pitot tubes for measuring flow in irrigation wells.