Author
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Replogle, John |
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Submitted to: Irrigation Journal
Publication Type: Popular Publication Publication Acceptance Date: 3/1/1998 Publication Date: N/A Citation: N/A Interpretive Summary: Irrigation is seen by some as an environmental disaster to the earth. But placed in perspective with what might have been, we should remember that irrigated agriculture grows one-third of the total crop harvested. This irrigated harvest is produced on one-sixth of the world's crop land and is worth one-half of the crop value. Without irrigated agriculture, expansion nof cropped land into humid areas would have been needed, and it is doubtfu that the rainforests of the world would still exist. Even with this perspective, we have a long ways to go to really make irrigation as efficient as it needs to be to continue to outpace the world's population bulge, expected to peak above 10-12 billion people, and still protect the environments of the world in a meaningful sense. The measurement of applied irrigation water is one of the major links in efforts to improve irrigation management to achieve this needed efficiency. This short article describes a couple of recent developments in flow-rate measurement of irrigation water that help to make field measurements more convenient and more economical. One deals with measuring flows in earthen canals and the other with flows from irrigation wells. Technical Abstract: Two recent developments in flow measuring devices are discussed. One makes measurements in small earthen canals and furrows more convenient, and the other offers an economical way to measure flows from an irrigation well or to check a flow meter installation. Concerning canals, a common false perception by many irrigation water users is that flow measuring flumes and dweirs significantly and harmfully restrict flow because they see ponding upstream of the flume or weir. These perceptions cause opposition to flow measurements and thwart proper irrigation water management. To address this problem, a flow-measuring device (flume) was developed that could be adjusted vertically after installation in the field. Another development concerns irrigation wells that are widely used to pump water into canal systems. These wells usually spill directly and freely into the canal. Upstream elbows or other pipe fittings frequently produce a distorted flow profile that is detrimental to the proper installation and operation of commonly available pipe meters, such as propeller meters, paddle-wheel pipe flow meters, and end-cap orifice meters, particularly if the well outlet pipe is relatively short. When less than recommended pipe lengths exist upstream of the metering device, an economical method is needed for field checking an installed meter in this compromised situation. Such a device is discussed and is a Pitot-tube system that can be clamped to the outlet end of an irrigation-well pipe. Distorted flow profiles can be detected. Using this information, the meter technician can determine if a correction in the meter coefficient will suffice, or if flow conditioning equipment is needed, or whether flow conditioning equipment, if already installed, is working effectively. |