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The selection of a primary device (weir or flume) for a particular open channel flow application typically can be broken down into three decisions: First – should a weir or a flume be used? Second – which style of weir or flume should be used? Third – which size…

Customer - Portland Water Bureau Portland Water Bureau had been using painted steel weir boxes to monitor its Bull Run Watershed dams.  The longevity of these weir boxes was never very high and several sites have had boxes placed and replaced over the years.  Also,…

There are six standard angles for V-notch weirs:  22-1/2º, 30º, 45º, 60º, 90º, and 120º, but from time to time this range of sizes is not enough. Sometimes there is a need to correct for a weir plate cut at an incorrect angle.  While other…

Let’s face it – we are all under pressure to save money and accomplish our jobs at a minimum of cost.  In stream gauging, it is tempting to use wood (usually plywood) to make a weir from.  Why not?  The shape of a weir is deceptively simple - just a…

Staff ("head" or "level") gauges provide a quick, visual indication of the level of water in a channel, flume, or weir. Although they should not be solely relied on when more precise level measurement devices are available, staff gauges allow operators to quickly gauge the…

Historically, mines were often abandoned without proper (if any) cleanup.  This lack of remediation and cleanup has meant that as water rises in the mine, pollutants, sediment, and debris can all enter what can become a flow of water out of the mine.   Flow monitoring…

Let’s not kid ourselves – landfill leachate is some nasty stuff. If it has gone into the landfill, there is the likelihood that it has concentrated in the landfill.  This environment can make it exceedingly challenging for primary devices (Flumes, Weirs, and…

Green roofs have grown in popularity in the US in the past decade.   Popularized in Germany begining in the 1960's, green roofs have shown to provide benefits to the building owners and society as a whole. WIth this popularity comes a desire to best utilize the…

In situations where flow rates are expected to vary widely, the use of a compound weir may be an appropriate solution.  The most common compound weir consists of two stages, a rectangular notch with a 90º V-notch cut into the center of the crest - but it does not have…

Weirs are best used to measure flows that contain only small amounts of suspended solids.  Unfortunately in surface water applications, the amount of solids present in the flow stream cannot be controlled.  Unlike flumes, which tend to be self-cleaning, weirs require…

People make mistakes.... The majority of errors in open channel flow measurement result from designers, installers, or operators - not from the equipment itself.  These errors result from a vareity of sources - from a lack to training to inattention to detail - and are…

In talking with customers about weirs, we run into two common misconceptions.  The first misconception is that weirs can read down to zero – that there is no minimum head.  The second is that weirs are more accurate at these flows than flumes. Unfortunately, both…