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When using a Parshall flume to measure pipe flow, it is important that sufficient upstream distance be provided to allow the flow to become tranquil and to assume a normal velocity profile as it enters the flume. The most effective method of transitioning pipe flow into a…

The USGS Portable Parshall flume is a modification of the standard Parshall flume where the discharge section has been removed.  The purpose of the modification is to reduce the weight of the flume and to make it easier to install. With the discharge section removed, the…

Customer – University of Louisville - Stream Institute The Stream Institute at the University of Louisville is an interdisciplinary applied research program in the Department of Civil and Environmental Engineering.  The work of the Institue is primarily concerned with…

Every year at Openchannelflow we talk with several hundred consultants, researchers, contractors and end-users about their flow monitoring needs. Because we work extremely hard at answering all questions "flow” on this web site – and this blog in particular - we are…

Parshall Flume Metering Manholes are an excellent solution to the problem of how to monitor below-grade piped flows.  Integrating the popular Parshall flume into a fiberglass manhole, Parshall Flume Metering Manholes are complete, factory-integrated structures capable of…

End adapters are specially shaped transitions that are molded or secured to the inlet and outlet ends of Parshall flumes to connect then to inline piping so that flow can be measured.  End adapters serve to transition flow from the round pipe to the rectangular cross-section…

Parshall flumes – like all flumes - are obstructions placed in a flow stream that produce backwater.  This backwater extends upstream of the flume and raises the water surface in the approach channel.  The difference in water surface elevation with and without the…

Large Parshall flumes – those with throat widths larger than 144-inches – are primarily used to measure the diversion of water from streams, lakes, and other primary sources of surface water to smaller irrigation distribution systems. The flumes are not commonly used…

Less well known than their more numerous Rectangular throated brethren, Trapezoidal Cutthroat flumes are a class of (3) flumes that combine the low flow sensitivity of the Trapezoidal flume with the simple, throatless design of the Cutthroat flume. Trapezoidal Cutthroat flumes…

Small Parshall flumes, those from 1-inch to 3-inches in size, are well suited to a variety of applications, from stream gauging to industrial pretreatment monitoring.   The flumes posses good flow ranges, are able to measure low heads / flow rates with accuracy, and are…

In The Parshall Flume (1936), Dr. Parshall indicatd an approach velocity of about 1 ft/s was desireable and that the Parshall flume was intended to operate when the approach velocities were moderate.   Parshall flumes, while showing some insensitivity to approach velocities,…

Trapezoidal flumes are popular choice when industrial users need to measure pretreatment discharges.  The flumes provide: Good resistance to submergence Pass solids and sediments well Able to accurately measure low flows Suiteable for sanitary / mixed industrial flow streams…

Many people confuse a flume’s resolution with its accuracy and use the terms interchangeably.  The two, however, are distinct from each other.  A flume may have good resolution, but poor accuracy, and vice versa.

It’s not uncommon in catchment, surface water, and watershed applications to only need to monitor a site for several seasons or years.  Sometimes, in fact, there is a need to be able to dismantle the installation after the monitoring period has been completed. …

For flume and weir applications where the flow entering the device may not be as well distributed as one would like / or where the velocity profile needs adjustment, perforated baffle plates can be a good choice. Used in a series of two or more, perforated baffle plates help…

Case Study Portable stream gauging Customer Warner College of Natural Resources - Colorado State University Background Warner College of Natural Resources (WCNR) at Colorado State University (CSU) is the largest named and most comprehensive natural resources program in the United…

One advantage that the Cutthroat flume has always had over other short-throated flume like the Parshall or Trapezoidal was the ability to develop intermediate width flumes for one of the four standard lengths.    But what if the standard lengths don’t yield a…

RBC flumes are small, portable long throated flumes designed specifically for use in small earthen channels and furrows.  The five flumes are scale models of each other, with each flume possessing a trapezoidal throat varying in size, bc, from 50 to 200 mm [1.968 to…

Thin-plate weirs, when properly installed and maintained, are one of the most accurate means of measuring open channel flows.  Under field conditions, though, without proper sizing or regular maintenance a thin-plate weir will become increasingly less accurate over time.

A problem with the application of thin-plate weirs in the field is the lack of proper conditioning of the flow before it reaches the weir crest. Baffles, placed upstream of the point of measurement, can be used to correct both poor approach velocity profiles and surface…