A check dam is a small temporary barrier built across a swale, ditch or drainage channel. It slows the flow so the channel doesn't scour, and lets some sediment settle behind it. Check dams are mainly an erosion control for channels, with a secondary sediment-trapping benefit.
Materials
| Type | Notes |
|---|---|
| Rock (riprap or aggregate) | Durable, handles higher flows; can be left as permanent protection in some designs |
| Fiber rolls or compost socks | Lighter flows and small swales; staked and trenched |
| Manufactured checks | Triangular foam/fabric dikes, reusable and quick to install |
| Sandbags or gravel bags | Short-term or emergency use |
The spacing rule
Space check dams so that the toe (base) of the upstream dam is at the same elevation as the top (crest) of the downstream dam. That way the water behind each dam reaches the next one, and the whole channel is a series of slow pools.
Spacing (ft) ≈ dam height (ft) ÷ channel slope (ft/ft)
Design details
- Keep dams low, commonly no more than about 2 feet at the center, per your BMP manual.
- Make the center lower than the edges (a notch, often about 6 inches lower) so overflow stays in the middle of the channel instead of cutting around the ends.
- Extend the ends up the channel banks above the expected water level.
- Protect the area just downstream from scour where water drops over the dam.
Installation
- Place dams perpendicular to flow, starting at the downstream end.
- For rock: key the rock slightly into the channel bottom and banks; build to the design height with the center notch.
- For fiber rolls or manufactured checks: trench and stake per the manufacturer.
- Confirm the top of each dam lines up with the toe of the one upstream.
Where not to use them
- In live streams or wetlands (permits for work in waters are separate).
- In channels where ponding would flood roads or properties.
- As the only sediment control for large disturbed areas.
Maintenance
Inspect after storms. Remove sediment when it reaches about half the dam height, repair flow around the ends, replace displaced rock, and remove temporary dams once the channel is stabilized, spreading the sediment and stabilizing the area.
Sources and official references
Last reviewed: October 25, 2026 · Free general education based on the Clean Water Act, EPA NPDES rules and the EPA Construction General Permit. Your governing permit (EPA, state, tribal or local) controls. This is not legal advice, not EPA-approved, and not a California QSP/QSD or other state credential, and it does not issue a certificate. Nothing you enter on this page is saved or sent.