Blog

On the face of it, mounting a staff gauge on a weir plate to get the head / flow rate seems like a good idea. It works for on a flume, why wouldn’t it work on a weir? The problem is, as we have seen earlier, the water level in a weir pool draws down as the flow approach the…

A common problem in using Weirs to measure water flows is reading the flow level too close to the weir plate. To understand why this is a problem we need to look at what happens as flow travels through the weir pool and then over the weir crest.

We often talk about how OCF tried to sweat the small things. One of the items that we have focused on is our flow meter sensor mounting brackets. Many of the designs currently on the market show, what we believe to be, a "good enough" philosophy - that the brackets hold the…

The freeboard is the difference in height between the top of a flume or weir and the highest water level anticipated. Freeboard is a guard against overtopping by waves, unexpected rises in the water level, or miscalculation in the maximum anticipated flows. Freeboard is also…

During periods of rapid water level change, the level in a stilling well may lag behind those in the channel that it is measuring. This phenomenon is known as stilling well lag and is a result of head loss in the intake system. Stilling well lag may occur when the water level in…

In a suppressed rectangular weir, the nappe stretches from channel wall to channel wall. On the downstream side of the weir, the air under the nappe will become entrained in the nappe as it passes over it as it spills into the downstream channel.

One problem that we see again and again is how to measure open channel flow in partially full pipes. For applications where a device can extend off the end of the pipe a number of solutions are used, including: California pipe (which is extends vertically up from the pipe before…

In edge-of-field / runoff monitoring sites it is not uncommon to have flow running in ill-defined channels (versus creeks or small streams). The problem then becomes how to capture and direct the flow into a flume or weir to quantify and measure the flow. Here wing walls are a…

For industries required to measure and / or sample their effluents prior to discharging to a municipal sewer system or surface water, finding sufficient area to install a primary device can be a struggle. In many instances, it is difficult to find a site that provides sufficient…

Of all of Openchannelflow's products, our Weir Boxes receive the most calls for customization; more so than our flumes, manholes, or even equipment shelters.

Bubbler style flow meters provide the most accurate measurement of level in open channel applications; more accurate than ultrasonic or even pressure transducer flow meters. Using an internal air compressor to push a measured volume of air through a vinyl or Teflon bubbler line,…

The typical bracket used to mount an ultrasonic sensor over a flume or weir is a contractor fabricated one-off assembly. These assemblies often mount the ultrasonic sensor too high, too close to the flume / weir sidewall, or aren't sufficiently rigid - making accurate flow…