Parshall's flume, when placed in a channel, measures the flow of water as it uniquely relates to water depth. Department of Agriculture, Parshall noticed there was a severe lack of measurement structures that could effectively monitor stream flows. Parshall flumes were developed by Ralph L. The Parshall flume was, and in some cases still is, the standard measurement device for open channels, although it was not conceived as a primary flow measurement for many of the applications in which it has been used over the past 90 years. The geometry of such a carefully-constructed restriction establishes a verifiable relationship between the liquid level upstream or within the primary element, and the flow rate through the device. For any open channel that is free-flowing through a specific controlled primary metering element, the flow height (head) can be an accurate indicator of the flow volume and therefore provides reasonable measurement of the flow rate.īut a primary flow meter is necessary to convert channel flow to a cross-section for repeatable head production, thereby delivering repeatable accuracy. A common way to gauge flow through an open channel is to measure the height or "head" of fluid as it passes a restriction (like a flume or weir) in the channel. Open-flow channels are not pressurized, and therefore full-pipe measuring elements such as Venturi, electromagnetic or strap-on transit-time flow meters are not viable. However, one of the more unique measurement landscapes is that of open channels - which include irrigation ditches, streams, water works processes, and sanitary and stormwater sewage system flows - where the flow of liquids along a free surface is occasionally "open" to the atmosphere.Įffective flow measurement of an open channel can prove to be challenging. Depending on the situation, the flow of liquid and the location where water measurement is required, there is most likely an effective fluid metering solution. In the world of effective and accurate water measurement, there are several tools to choose from. Open channels can be tough to measure but careful attention to flow height and flume position can help boost accuracy and verifiability.
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