Stilling wells are used in a wide variety of flow channel measurement setups, whether you’re using a flume or a weir. This is because they work to condition the flow, allowing for accurate measurements to be taken. Before you utilize one in your flume or weir, however, there are a few factors you need to consider. Here’s what you need to know about stilling wells.
Increased Depth
Stilling wells will always have a bit of water in them, even if the flume or weir is completely empty. This is because a stilling well’s floor is set lower than the floor of the weir box or flume. Note that this is by design, because the standing water is necessary for proper readings when measuring factors like pH and conductivity. Just keep in mind that the water will need to be refreshed now and then, as the conditions will change in standing water over time if it’s simply left alone.
It’s important to remember that this increased depth can be a problem when you’re dealing with a flow that has a lot of sediment. The dimensions of the well and its usefulness can be diminished by a buildup of sediment at the bottom. You can counteract this by making the floor of the well flush with the floor of the flume or weir, but that adds another problem altogether. It means that low flows can essentially ignore the stilling well, rendering it useless.
Stilling Well Styles
There are two primary styles you can opt for when choosing a stilling well. You can either opt for one that’s attached or one that’s detached. Attached stilling wells are molded to be part of the flume or weir box in the case of fiberglass constructions. Detached stilling wells are connected via tubing and are located a distance away from the flume or weir itself. Both perform the same function, but the different styles exist as a matter of convenience.
Imagine you have a flume that doesn’t utilize vertical walls, such as a trapezoidal or RBC flume. You can’t exactly attach a vertical stilling well to the side given the orientation of the walls. For these, you’ll need to opt for a detached stilling well, as tubing can easily be connected to an angled sidewall. Given the lag caused by the tubing, however, detached stilling wells generally need to have larger openings.
Freezing Water
When your stilling well is set up in a place that experiences freezing temperatures, you’ll have to take some extra steps to keep it free of ice. Fortunately, there are several ways to accomplish this. The first is by using electric immersion heaters. The only downside is that they require a power source to function, and that can be a bit difficult if your flow channel is in a relatively remote location. If the cold weather isn’t consistent, the immersion heater could also cause some of the water in the well to evaporate.
The second option is to put oil in the well on the surface. Oil and water don’t mix, so the oil should act as a protective layer for the water, preventing the formation of ice. Just note that you’ll have to adjust your measurements a bit because the oil adds height to the liquid in the well. Be careful of low flow conditions as well because the oil can drain out if the flow gets low enough.
Stilling Wells From Tracom
Keeping what you need to know about stilling wells in mind, it’s time to get your own. Contact Tracom today for a custom stilling well that’s perfectly suited for your flow channel conditions.
