A weir is one of the most useful tools you can install in your water management system. However, like most tools, getting the most out of your weir depends on understanding how to use it correctly. Inexperienced weir operators often have trouble reading the levels in the weir, potentially putting the success of your system at risk.
Before installing a weir in your system, it’s a good idea to learn the correct way to read your weir so that you can take the accurate readings that you need. Learn how to correctly read a weir so that you can ensure the success of your operation and learn how you can purchase high-quality, durable weirs.
The most difficult part of reading a weir is choosing the correct point of measurement. Generally, this is because measuring from a weir is much different than measuring from a flume. With a flume, your point of measurement is in the flume itself, which is very convenient. If you use a weir, you will need to take your measurement upstream of the weir.
Because of a standard weir’s design, the water approaching and passing over the weir crest will experience a drawdown, which is why you cannot measure directly at the weir. To avoid the effects of the drawdown, you will need to take your measurements at a distance that equals three to five times the maximum head upstream of the weir crest.
Weir Face Measurements
One of the biggest mistakes that novice weir operators make is attempting to take measurements at the face of the weir. The surface of the water in your system will drop as its velocity increases while approaching the nappe. This drop is most pronounced at the face of the weir and, if you measure at this point, you will only get an idea of the direction of the flow and not the flow rate.
When used correctly, weirs have a +/-2% accuracy. However, if you measure at the face, this accuracy will be significantly reduced. Make sure your operators know that they should refrain from measuring at the weir face if you want the most accurate readings possible.
Developing your weir pool is an important part of effectively using your weir. To do this, your weir crest needs to be positioned correctly, which is generally two times the maximum anticipated head. Your gauge zero also needs to be set at the zero reference elevation for head measurement.
Weirs differ from other measurement devices in that there will be some water below the gauge zero. Because of this, many operators attempt to measure from the surface of the water to the floor and then deduct the height of the crest to determine the head. However, this method fails to take into account sedimentation or crest shift.
Read a Weir Correctly
As long as you use the correct method for reading your weir, you can easily maintain the accuracy of your system. To make sure you can read a weir the right way, you need high-quality tools, which you can find by shopping with Tracom, FRP.
Tracom provides the fiberglass weirs that you need to ensure the consistent success of your operation. Contact us today for more information.