Stone Check Dam

A stone check dam is a barrier constructed of stone that reduces the flow velocity of runoff, while minimizing channel erosion and promoting sediment deposition. Stormwater enters a swale or vegetated ditch and, under normal circumstances, is ponded temporarily behind the check dam in the sediment control basin. Ponding allows sediment and other pollutants to settle out, while allowing some water to infiltrate and evaporate. The water that remains is slowly passed through the check dam continuing on towards the outfall. In high flow situations, runoff is conveyed over the top of the stone. Check dams are best used in conjunction with other BMPs, such as Erosion Matting.

Stone check dams may be permanent or temporary and can be used in swales or vegetated ditches with a maximum drainage area of 10 acres. Check dams are often used on sites with slopes that are steeper than desired. Depending upon the slope of the channel and the individual site, multiple check dams may be needed to control runoff velocity.

Advantages

• Low cost
• Relatively easy to construct
• Reduces erosion and promotes sediment deposition

Disadvantages

• Requires periodic sediment removal
• Temporary check dams may be difficult to remove
• Effective only in channels that drain 10 acres or less
• Ineffective with large storm events

Check dams should consist of, at a minimum, a 1-foot layer of 1-inch washed stone over a 1-foot layer of 3 to 6-inch clear stone, free of fines and sand, underlain with a geotextile fabric. The size of the structure will depend upon the site, but should be 1-5 feet in height; have a minimum width of 2 feet; and should extend across the entire conveyance structure. In addition, the slopes should have a maximum ratio of 2:1, as greater slopes may become unstable and require excessive maintenance. The center of the check dam should be, at a minimum, 6 inches lower than the edges to allow water to flow over the top of the structure.

The sediment control basin, which allows sediment and other suspended particles to settle out before passing through the check dam, should be constructed at the upstream foot of the check dam and extend across the entire conveyance structure. Sediment control basins should be sized according to the individual site characteristics, but must be at least 2-feet deep and 6 feet long to provide adequate storage capacity, with slopes not exceeding a 2:1 ratio.

To discourage concentrated flow, water velocity in the channel can be reduced by using multiple check dams. The distance between check dams will depend upon the slope of the conveyance structure, but should be spaced so that the base of the upstream check dam is even with the peak of the downstream structure. As the slope of the conveyance structure is increased, the number of check dams that will be needed to prevent concentrated flow in the channel increases as well. As a result, check dams used in conveyance structures with slopes greater than 6% may not be practical.

Table 1: Recommended Spacing of Check Dams

• Check dams should be underlain by a geotextile filter fabric
• Check dams should be constructed immediately after grading is completed on the conveyance structure
• Caution should be taken to ensure that objects down stream of the check dam are not damaged from dislodged stones

• Check dams should be inspected for damage after each storm event - all damage should be repaired immediately
• Sediment that accumulates behind the check dam should be removed as necessary
• Additional stone may need to be added to ensure that the check dam retains its design characteristics

The efficiency for this practice is derived from the reduction in slope length that it provides. To calculate the efficiency, simply use the new, reduced slope length in place of the pre-existing one in the USLE and recalculate. The difference between the two completed equations is the efficiency for the practice.

• Wisconsin DNR Ditch Check Technical Standard 1062