Sediment Control

Containing eroded soil on the project site will be the responsibility of some IRVM programs. Basic sediment control products likely to be used on county rights-of-way are described below.

Wattles, sediment logs and filter socks

Wattles and sediment logs are tubes of straw, coir or excelsior fibers encased in burlap or degradable plastic netting and anchored by wooden stakes. Both filter sediment and slow water flow. Wattles and logs containing densely packed material – especially straw – are good as slope interrupters. Excelsior logs are more porous and less likely to float, so are better suited for ditch checks. Both are good for perimeter applications and inlet protection.

Filter socks are degradable tubes filled with compost, generally used for perimeter control or at intervals along a slope to capture sheet flow. To enhance sediment control, polyacrylamide (PAM) may be added to the compost. PAM captures clay particles creating cleaner runoff.

Wattles, logs and filter socks are usually easy to install and can be put on bare soil or over erosion control blankets.

Silt fence

Silt fences are geotextile barriers trenched in to the ground and supported by posts. They are useful on perimeters and in channels with relatively low flow. Silt fences filter out small amounts of sediment as runoff passes through the fabric. They need to be kept clean to function properly and must be removed after final stabilization, but are easy to install and relatively low cost.

Silt fences are not effective in high-volume flows and should not be used as a check dam. During moderate or heavy rains, a silt fence check dam will concentrate water from the entire channel, along with the water’s energy. This concentration either goes around the outside of the fence or over the top at the lowest point. It can also go underneath the fence, causing erosion.

Silt fences are ineffective when improperly installed, and improper installation is common. To avoid the problems inherent with these practices, follow up-to-date specifications such as those found here:

Check dams

Check dams should be constructed of clean rock, permeable plastic berms or similar products. Unlike silt fence, check dams do not cause water to dam up; they let water pass through – slowing its velocity and dissipating its energy.

Sedimentation can occur on the upstream side. If it becomes too great the check dam will function as a waterfall and the project may begin to fail. Monitor and excavate the upstream side if necessary.

Plastic berms should not be placed in areas susceptible to filling with debris (e.g., corn stubble from a field waterway).  One heavy rain can cause these berms to fill with stubble, creating a dam.

Improper check dam design is not uncommon and can cause project failure.  Follow current design specs, and account for the individual characteristics of each site.

Roadside manager insights

If a rain event is relatively small, silt fences will function properly. But small rain events typically cause little to no erosion. Silt fences may be good for PR but they create a point of failure for the project. A roadside is essentially a headwater stream. Stream dynamics show that flow = area*velocity. When the water from a flat, six-foot wide channel is concentrated into a width of typically less than a foot at the low point of a silt fence, the water’s velocity increases substantially, thus erosion is caused instead of prevented.

-Jim Uthe, James Devig, Dallas County, 2024

Rock checks should mostly be below ground. The “waterfall” problems can be eliminated if the check doesn’t extend above ground-level.

-Wes Gibbs, Jones County, 2024

Erosion and sediment control web sites