When setting the flume in concrete, pay attention to the following points: Submerged flow conditions are usually avoided to allow use of the standard discharge tables and depth measurements at Ha only. Observe elevations during design & installation so that modular flow, also known as "Free Flow" conditions are always present. The standard flow tables must be corrected when the Submergence Ratio, Hb/Ha, expressed as a per cent, exceeds the following values: Submerged flow conditions occur when the resistance to flow in the downstream channel becomes sufficient to reduce the velocity, increase the flow depth, and cause a backwater effect at the Parshall flume. A large fall or steep slope immediately downstream of the metering station can eliminate the possibility of submerged flow conditions. Long, narrow, flat or undersized channels can result in a backwater effect at the flume and should be avoided. Downstream channel: The downstream channel should not permit submerged flow conditions to occur.
Crest of the flume: The crest of the flume (the floor of the converging section where depth measurements are made) must be level both longitudinally & transversely.A 1:4 sloping ramp upstream should be provided for flumes that must be installed above the channel floor. A slope of almost flat, to 3% maximum, for very small flumes, and 2% maximum for larger flumes is the ideal slope value. The upstream channel slope should not allow excessive velocity at the flume. Channel turns, tees, elevation drops or other obstructions should be avoided. Upstream conditions: Upstream conditions should promote laminar flow conditions at the flume inlet.What are the three areas you should be concerned with for successful installation of a Parshall flume? Flumes are restrictions in the channel and consideration should be given to the effect of the resulting backwater on upstream drains and channel walls or banks. In general, the smallest flume of adequate capacity is selected. Sizing of flumes is based on anticipated normal and maximum flows. What size Parshall Flume should I purchase?
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