Erosion and sedimentation are two terms commonly used in construction stormwater management, and while they are closely related, they describe different processes. Understanding the difference is important for selecting the right Best Management Practices (BMPs), preventing sediment from leaving a construction site, and maintaining stormwater permit compliance.
What Is Erosion?
Erosion occurs when soil is loosened and transported by forces such as rainfall, flowing water, and wind. On construction sites, clearing vegetation, grading, excavation, and other land-disturbing activities can expose soil and make it more vulnerable to erosion.
When rain falls on exposed ground, water can detach soil particles and carry them across the site. Concentrated runoff may also create rills, gullies, and channels that move larger amounts of soil.
Common signs of erosion include:
- Rills and gullies forming on slopes
- Soil washing away from disturbed areas
- Exposed roots or undercut areas
- Sediment moving toward storm drains or drainage channels
- Loss of soil around recently installed BMPs
How to control erosion: Erosion control focuses on keeping soil in place. Depending on site conditions, BMPs may include temporary or permanent vegetation, mulch, erosion control blankets, slope stabilization, and reducing the amount of exposed soil at any given time.
What Is Sedimentation?
Sedimentation occurs when soil particles that have been transported by runoff settle out of the water. As water slows down, suspended particles can accumulate in low-lying areas, drainage channels, stormwater ponds, or other locations where flow becomes less turbulent.
On construction sites, sedimentation is often visible as muddy deposits near storm drain inlets, along the edges of waterways, or at the bottom of sediment basins and other collection areas.
Common signs of sedimentation include:
- Sediment deposits around storm drain inlets
- Mud or silt accumulating in drainage swales
- Sediment buildup in sediment traps or basins
- Discolored water leaving a disturbed area
- Deposits beyond the construction site’s perimeter
How to control sedimentation: Sediment control focuses on capturing or filtering soil particles before they leave the site. Depending on the conditions, BMPs may include properly installed inlet protection, check dams, sediment basins, filter socks, and perimeter controls. These measures must be selected, installed, and maintained according to site conditions and applicable permit requirements.
Why the Difference Matters
The key difference is where each process occurs in the movement of soil. Erosion is the detachment and movement of soil from the ground. Sedimentation is the settling of transported soil particles.
This distinction matters because a BMP designed to control sediment may not prevent erosion from occurring in the first place. Likewise, stabilizing exposed soil does not eliminate the need to manage sediment that has already entered runoff.
For example, consider a construction site with an exposed slope. During a storm, rainfall washes soil down the slope and into a nearby drainage swale. The soil washing away is erosion. When the water slows and the soil settles in the swale, that is sedimentation.
Installing a sediment barrier at the bottom of the slope may help capture sediment, but it does not address the source of the problem. Stabilizing the slope with appropriate erosion control measures can reduce the amount of soil being displaced in the first place. Using both approaches, where appropriate, provides a more effective stormwater management strategy.
A Proactive Approach Makes a Difference
Erosion and sedimentation are connected, but they are not the same problem. Erosion control helps keep soil in place, while sediment control helps prevent displaced soil from traveling off-site. Both are important parts of an effective construction stormwater management program.
By identifying the source of soil movement, selecting appropriate BMPs, and keeping controls properly maintained, construction teams can reduce sediment impacts, avoid recurring issues, and support stormwater compliance throughout the project.
Need help with construction stormwater compliance? Summit Services Group provides stormwater inspections, SWMP support, and practical guidance to help Colorado construction teams identify issues and maintain effective BMPs. Contact Summit to learn how we can support your next project.