Public Works & Utilities

If your construction project is like most, you performed some grading of your project site, removing some or all the existing vegetation or ground cover.

When rain falls on exposed soil, it can wash soil away from your project site. The water runoff can erode bare ground, wash away valuable soil, making landscaping more difficult and costly. It also carries sediment, nutrients and other pollutants into streets, gutters and ditches, where it then travels untreated to lakes, rivers, streams or wetlands. The City of Duluth has many trout streams that are particularly sensitive to environmental impacts, making the protection of wetlands, stormwater management features and various acts of pollution prevention extremely vital. Sediment-laden runoff can also clog storm downstream storm sewers, stormwater filtration systems and require increased system maintenance.

The property owner and hired contractor are both responsible and required to take steps to keep soil and sediment from leaving your site. You can help protect the environment by ensuring that soil and sediment are not washed off your property, and that grass, native plants or other vegetative ground cover become well established once earth work stops.

Quick Summary of a Few Examples of Risks Caused by Sediment Runoff:

Construction Project Money Loss: Loss of valuable soil from site, making landscaping more difficult and required more equipment/labor costs to correct. Possible hefty violation fees from the city and/or Minnesota Pollution Control Agency if site is found to be in violation.

Environmental Impacts: Sediment runoff can smother aquatic plants, cloud water, and disrupt fish habitat and spawning gravels, impacting the entire ecosystem.

Flood Risk: Sediment buildup in waterways, ditches or the storm sewer can reduce their capacity, increasing flood risk downstream.

The property owner and hired contractor is responsible for inspecting and maintaining temporary stabilization measures until permanent ground cover is established on the project site. Below are some examples of temporary stabilization measures. You can find other helpful resources on MN Stormwater Manual here.

Vegetated Buffers: Vegetated buffers are areas designated to remain undisturbed to protect trees, lakes, bluffs, or natural areas. Buffers should be marked and maintained around all resources requiring protection.

Silt Fence: Silt fence filters sediment from runoff by allowing water to pass through a geotextile fabric or by creating a pool to allow sediment to drop out of the water column. Silt fences are installed primarily at downslope boundaries of the work area but can also be used around the perimeter of stockpiles.

Fiber Log: Fiber logs include straw, wood, or coconut fiber logs, compost logs, and rock logs that slow water and filter sediment. Fiber logs are used for inlet protection, ditch checks, and as perimeter control where silt fence is infeasible.

Construction Entrance: A construction entrance is a bed of rocks, slashed wood mulch or other commercially available mat/product that helps to remove sediment from vehicle tires. Construction entrances should be placed at all site access points. For rock construction entrances, the use of 1 1/2 inch – 3-inch clear aggregate is recommended. Periodic cleaning or replacement is recommended.

Grade Breaks: Grade breaks are changes in slope that break up concentrated flow, preventing the formation of gullies. Grade breaks should be incorporated into long slopes

Temporary Seeding: Temporary seeding allows plants to stabilize the soil through vegetation and root growth. A large variety of plants are available for temporary seeding of different conditions; the most common are rye grass, winter wheat, and oats. Temporary seeding can be affordable and extremely effective way to reduce soil erosion through longer duration projects.

Erosion Control Blanket: Erosion control blanket is a mat made of netting layered with straw, wood, coconut or fibers that prevents erosion by sheltering the soil from rainfall and runoff while holding moisture for establishing plants. Erosion control blankets should be made with natural netting.

Mulch/Hydraulic Mulch: Mulch is fibers, compost, wood chips, straw, or hay that is applied as a cover to disturbed soil. Mulch reduces erosion by absorbing energy from rainfall and runoff and provides protection and moisture for the establishment of vegetation, when properly disc anchored or spread.

Temporary Pipe Downdrains: A temporary pipe downdrain conveys runoff down slopes in a pipe so that runoff will not cause erosion. Pipe downdrains are installed where concentrated flow would drain onto a disturbed slope

Flotation Silt Curtain: Floatation silt curtain is fabric fence installed in water bodies to contain sediment near the banks of the work area. Must be used in conjunction with other sediment control techniques.

Rock or Compost Bags: Rock and compost bags are filled bags that are used to filter water, control ditch grade, or to provide inlet protection. If they are used as inlet protection, care must be taken to ensure that they are not damaged by vehicle traffic.

Rock Check Dam: Rock check dams are rocks piled across a ditch to slow flows and capture sediment. Rock checks are installed perpendicular to flow and should be wide enough to ensure that flow remains in the center.

Riprap: Riprap is appropriately sized rocks that reduce the energy of fast-moving flows. Riprap is used along channels or outfalls and is typically crushed or angular to lock together and prevent slippage or movement.

Temporary Sedimentation Basin: Temporary sedimentation basins are depressions that capture runoff to slow the flow of water and allow sediment to settle out. Temporary sedimentation basins are required on some large-scale earth disturbances and should be appropriately sized.

Filter Bag: Filter bags are mesh bags that capture sediment but allow water to pass through. Filter bags are installed in storm drain inlets and must be maintained regularly.

Stabilization is required under the National Pollutant Discharge Elimination System (NPDES)/State Disposal System (SDS) General Stormwater Permit for Construction Activity.  If your site(s) will not be completely vegetated by fall, all areas with exposed soil must be seeded and mulched using the specifications outlined below (or a similar approved technique). 

Stabilization must be initiated immediately to limit soil erosion when construction activity has permanently or temporarily ceased on any portion of the site and will not resume for a period exceeding 14 calendar days (7 days for sites discharging to special or impaired waters).

Temporary cover must be established prior to frozen ground conditions.  Winter Wheat (MNDOT 21-112) is good, available and cost effective for fall temporary seeding for areas that will be re-disturbed in the spring. Dormant seeding is done in the late fall after the soil temperature remains consistently below 50 degrees Fahrenheit (depending on the mix).  Disc anchored straw mulch or other erosion control is necessary with all temporary, dormant, or final seeding. 

Fall and Dormant Seeding Dates

For areas with steep (3:1) or problematic slopes, consider natural netted erosion blanket, or other stabilization techniques listed in the permit.  Further, make sure all drainage ways, ditches, and gullies are stabilized so they can withstand channelized flows / velocities.