How to Measure Dam Seepage Flows

Dams have been used for thousands of years since our ancestors learned how to tame the environment around them. They still play an important role in our lives today, as dams are used for controlling rivers, producing energy, protecting against floods and more. There’s always seepage, however, and you’ll need some way to measure that seepage. Both weirs and flumes can work, but the best option will depend on your unique conditions. Learn how to measure dam seepage flows, and discover whether a flume or a weir box would work best.


If you’re dealing with dam seepage that has excessive sedimentation, a flume might be your best bet. Most solids will pass right through the throat of a flume depending on its design, while other designs that involve a riser box can be used to catch solids if necessary. In fact, a riser box functions similarly to a weir box, so you can view it as a compromise between the two general wastewater measurement devices.

Weirs are notorious for their inability to deal with sedimentation. Simply due to the design of a weir box, sedimentation will inevitably build up over time. While it won’t necessarily ruin a weir box, it does mean you’ll have to clean it fairly regularly, and that can be time-consuming and tedious. An inlet baffle plate can be used to counteract this trend, but depending on how severe the sedimentation is, you’ll probably be better off with a flume.


Both weirs and flumes leave footprints behind, or rather a portion of land that must be dedicated to the installation and operation of the wastewater measurement device. If you have limited space to work with, a flume is going to be your best bet because they tend to have a much smaller footprint. A flume can be bigger than a weir box, but the weir box must also include a weir pool, which is relatively large.

The upstream weir pool is essential to the proper functionality of a weir box, and that means sizing it correctly. Without the proper upstream conditions, all measurement efforts will be thrown off, rendering the process useless. When it comes to seepage flows that may read both high and low at different times, there generally isn’t enough room for a properly sized weir pool.


One of the most important factors in any flume or weir box is accuracy. Anything less than pinpoint accuracy will largely make all measurement efforts useless. The best option mostly depends on the head and flow rate of your flow channel. Weirs are often considered to be the best at providing accurate measurements at low flow rates, but that’s only true some of the time. In fact, a weir is unable to deal with a head lower than 0.2 feet. Meanwhile, a 1-inch Parshall flume can measure with a head as low as 0.6 inches.

While flumes have a wider range, weirs do tend to be more accurate if the flow rate is manageable enough. For example, a weir measuring with its minimum head of 0.2 feet can offer accuracy of about +/- 2%. Meanwhile, the best a flume can offer is +/- 3%, and that’s only when you have unique flow conditions that specifically allow for that kind of accuracy.

Measuring With Tracom

You now know how to measure dam seepage flows, so it’s time to get your hands on flumes, manholes & weir boxes that fit your flow measurement needs. Tracom is happy to help with our team of designers that will work with you to make the perfect fit. Contact us today to get started.

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