Weir Flow Guide

The key in running a successful water management operation is having the right tools for accurately measuring flow. While there are several tools that you can choose, one of the most effective is a weir. Installing a weir in your system provides several benefits, including consistently accurate readings and extreme durability. Weirs can also be installed in either a man-made or natural channel.

If you’re interested in using a weir for your flow management needs, there are several factors that you need to consider. However, the most important issue is the flow regime that you expect in your system. Read about possible weir flow regimes, and discover how you can improve the accuracy of your readings by purchasing your flow measurement tools from the right source.

Free Flow

When you install a weir in your system, there are two possible flow regimes. The first, and most common, weir flow regime is free flow. Free flow, or modular flow, means that there are now downstream conditions that may restrict your weir discharge, meaning your flow will spill over the nappe of your weir into the air. Free flow requires that the lowest point of your weir crest is higher than the lowest downstream water level.

Both contracted and suppressed weirs can be used in free flow conditions — contracted weirs automatically aerate flow, suppressed weirs need a vented nappe for aeration.

Submerged Flow

If the downstream conditions in your system prevent free discharge from your weir, then the flow is considered to be submerged. This is also known as non-modular flow. When your flow is submerged, you will experience flow readings that are higher than your actual flow rate. As you might expect, this will greatly impact the success of your operation.

Submerged flow requires your operators to perform a submergence correction calculation. This can be very complicated, which is why it’s best to avoid submerged flow if at all possible.

Choosing Weir Flow Regimes

Now that you know a little more about weir flow regimes, it’s time to learn which is the right choice for your operation. If your main goal is to use your weir to measure flow, then you should strongly consider installing under free flow conditions. A weir that operates under free flow conditions will provide much more accurate readings and lead to a more successful operation.

If you want to promote free flow conditions, you may need to install your weir slightly higher than you might anticipate. Installing your weir so that it operates under free flow conditions is the right choice for nearly every water management system.

Flow Measurement Tools

When it comes to flow measurement, there’s almost no better option than installing a weir. Although free flow conditions are best, weirs are also accurate under submerged conditions provided your operators understand how to make the necessary corrections. After learning about the different weir flow regimes, you need to purchase a high-quality weir from a trusted source like Tracom, FRP.

Shopping with Tracom means having access to the best flow management tools on the market today, including accurate, durable weirs. Contact us today to get a free quote and to learn more about our weirs and other flow measurement tools.

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