Outlet control devices are critical components of stormwater detention and retention systems. They regulate the rate at which stored water is released from facilities such as wet ponds, dry ponds, and underground detention systems. Without a properly functioning outlet control device, a stormwater facility cannot meet its designed discharge rate, which can lead to downstream flooding, erosion, and regulatory noncompliance.

Most ponds and underground detention systems include an outlet control device designed to restrict the flow of water out of the system and into the drainage network or natural waterways in an effort to reduce erosion and downstream flooding. Outlet control devices come in many different forms, but usually include some type of low-flow orifice and a bypass mechanism.

The low-flow orifice is a small opening or a pipe designed to let rainfall runoff that’s being temporarily stored in the detention system slowly leak out of the system. Controlling the maximum flow rate of this water if the primary goal. The bypass mechanism is usually a type of weir wall or the rim of a vertically installed pipe that water will overtop when there’s too much water being stored in the system. This prevents water from backing up into buildings, flooding parking lots, or breaching pond embankments. Typically made from concrete, metal, or plastic, you can usually spot the outlet control device in a stormwater pond fairly easily, and now you know why they are there!

There are three primary things to check with inspecting an outlet control device. The most important – and hardest to observe – is the low-flow orifice. They can be difficult to inspect, as you may need special equipment or even confined space entry training to safely get a good view of the orifice. And because the orifice is usually a fairly small opening, they have a tendency to clog up easily, which can cause water levels to rise upstream, even to the point where flooding can become a concern. If you are able to easily access the low-flow orifice, get a good picture to include in your documentation.

Upstream of the low-flow orifice you may find a trash rack or some other device designed to prevent debris from clogging the low-flow orifice. Note any collected materials around the trash rack, and get good pictures. While you’re here, you can also observe the overflow or bypass mechanism to ensure that’s also free of foreign material that could affect its function. Note the overall condition of the structure, paying attention to corrosion or structural issues, as these devices are often ignored and can begin to fail over time.

Finally, it’s a good idea to check the downstream outlet of the device to ensure there’s no trash or erosion in the area. Again, get good pictures of any areas of concern.

If you need help with your inspection, getting a professional inspection from Exact is less expensive than you think, and we’ll provide thorough documentation, photographs, and corrective actions along with costs that are recommended.

Regular maintenance of your outlet control device is important, as its far easier than replacing it. Most maintenance activities will center around the trash rack and overflow to ensure collected debris is regularly removed to prevent back ups. These components are designed to capture larger items, so getting them removed is important. Maintaining the low-flow orifice can be much more difficult, but its just as important. A clogged orifice can lead to elevated water levels in the system and upstream flooding of parking lots and buildings, so you’ll want to make sure that’s clear and functioning properly.

Address any downstream erosion where the outlet control device discharges runoff, and be a good neighbor by collecting trash and other debris that might make the are unsightly.

If your outlet control device is showing significant signs of degradation, it may need to be replaced. Our team of licensed professionals can help you make that assessment, as well as perform any other regular maintenance that may be required. Replacing an outlet control device can be pretty involved, so it’s best to get a professional involved early in the process.

Installing a new outlet control device in a new project is a fairly simple process. While these structures can be quite large for big ponds and underground detention systems, most smaller ponds require a fairly simple structure. The process typically involves setting the structure in place, taking special care to ensure the orifice and the overflow elevations are right where they need to be, according to the design, and then routing the outlet pipe through the embankment to daylight or into the stormwater pipe network. It’s critically important to backfill the outlet pipe with compactible, impermeable material to prevent water from running along the pipe on the outside, create major erosion problems and potential flood risks.

Retrofitting or replacing an existing structure can be very involved, so it’s best to get professional help to determine the best path forward. There are often creative ways to salvage or modify the existing system, which can help reduce costs. Exact can help evaluate your outlet control device and provide an opinion on the most cost-effective way to keep your system running properly.

The most common types include riser structures (vertical pipes with orifice plates), weir walls, and multi-stage outlet structures that combine orifices, weirs, and emergency spillways in a single structure. The specific type used depends on the stormwater facility design, the required discharge rates for different storm events, and the local regulatory requirements. Exact Stormwater installs, inspects, and maintains all types of outlet control devices.

Outlet control devices should be inspected at least annually as part of the overall stormwater facility inspection. In practice, they should also be checked after significant storm events, as debris and sediment accumulation at the outlet is one of the most common causes of facility failure. In Virginia, DEQ inspection requirements cover outlet structures as part of the BMP inspection. Exact Stormwater can perform these inspections across all 12+ states in our service territory. Call (804) 302-5151 to schedule.

A failed or clogged outlet control device prevents the stormwater facility from releasing water at its designed rate. This can cause water to back up behind the structure, overtop the embankment through the emergency spillway, or flood surrounding areas. A malfunctioning outlet can also release water too quickly, causing downstream erosion and potential damage to neighboring properties. Both conditions can result in regulatory enforcement action from state agencies such as Virginia DEQ or Maryland MDE.