A weir is like a flume in that it’s used to measure open-channel flows, but there is a key difference that could determine whether or not a weir is right for the particular flow you’re working with. Weirs have to be cleaned regularly, so they’re best used for flows with a relatively limited amount of suspended solids within. Otherwise, the solids could get caught in the weir, pile up and throw off your measurements.
Flumes clean themselves due to their design, but weirs cannot offer the same convenience. With all the other benefits of a weir, it’s easy to see why one would choose a weir over a flume, but a weir’s cleanliness must always be a top priority. Learn why you need to keep weirs clean in order to keep your flow measurements accurate.
Accumulation in the Weir Pool
A weir works by effectively damming the water, which leads to an accumulation of solids in the weir pool upstream. It’s important to note, however, that weir pools have to be free of excessive solids like sediment and trash in order to properly regulate the flow rate. Even vegetation such as weeds from the surrounding area can have a negative impact on a weir’s proper functionality.
To ensure you’re getting accurate measurements, the weir pool must be regularly cleaned. That’s just the beginning, however, as the entire upstream channel must be properly maintained to ensure consistent functionality. If there are trees hanging over the channel upstream, for example, it’s typically a good idea to trim them or remove them entirely.
Weir Crest Shape
While every weir will need regular cleaning, the frequency of that maintenance can vary based on the weir crest shape. A V-notch, for example, gets dirty a whole lot faster than a rectangular weir. Of course, weirs that have to deal with high solid flows will also need more frequent cleaning than those measuring flows without many solids.
The crest of a weir has to be properly maintained for a wide variety of factors, including wear, oil, grease, obstructions and rounding. Precision is key when it comes to crest maintenance, as even the smallest dent can compromise the accuracy of flow measurements. The same applies if the crest is rounded or dulled, which will inevitably happen over time to all weir crests if not properly maintained.
Damage to the weir itself can severely compromise your measurements and render the entire weir structure pointless. Be sure to regularly check for cracks and leaks. Otherwise, a portion of the flow could simply bypass the weir entirely. It’s also essential to check any clean-out doors that may be installed for damage to prevent water from seeping through its seams.
Part of maintaining a weir is making sure it’s level. When a weir isn’t level with the flow channel, it won’t be able to properly measure the flow rate. Frost heave can make this a tricky issue to deal with, so you may have to modify the foundation of the structure to account for environmental factors.
Find a Weir Box of Your Own
Now that you know how to maintain a weir box and keep weirs clean, you can get one of your own. At Tracom, we provide high-quality, customized weir boxes that can help measure a wide variety of flow rates, all while leaving behind the smallest footprint possible. Take a look at our expansive selection of options and get in touch with us today to start the process.