Management

file

Why Is It Important?

Over Construction activities over one acre of land can increase sediment pollution by 20,000 to 30,000 times over adjacent undeveloped terrain.

  • Long Sediment in waters is a direct cause of the reduction in aquatic life.

Do’s and Don’ts

Disturbances Any disturbance, of ANY size, must be managed to MINIMIZE EROSION and CONTROL SEDIMENT input into Narragansett Bay.

What Is Soil Erosion?

Soil erosion is the detachment and movement of soil particles by water, wind, ice, or gravity.

What Is Sediment?

Sediment is the result of erosion. Once soil particles have detached from the surface, are transported from their site of origin and have come to rest on other ground surfaces or in bodies of water, watercourses, or wetlands, they are referred to as sediment.

Why Be Concerned About Soil Erosion And Sediment Control?

It's the Law: Soil erosion and sediment control requirements are a part of several Federal and State regulations and may be required by local ordinances as well.

  • Surface Water Quality: Urban runoff and construction site erosion have been identified as significant sources of non-point source (NPS) pollution to Narragansett Bay.
  • Chemical Pollutants: Chemicals, such as some pesticides, phosphorus, as well as toxicants and trace metals, can be transported with sediment to receiving waters where they cause additional damage to aquatic ecosystems.
  • Construction Sites: Construction site erosion is a significant source of sediment and other NPS pollutants. Soil erosion from a construction site without proper soil erosion and sediment control practices in place can average between 20-200 tons/acre/year--This is ten to twenty times greater than typical soil losses on agricultural lands.
  • Fish and Aquatic Plants: Suspended solids reduce sunlight penetration needed for aquatic plants, reduce survival rates for fish eggs, interfere with fish feeding habits, and clog and damage fish gills which increases risk of infection and disease. Sediment deposits destroy fish spawning areas, resulting in the loss of sensitive or threatened fish species, adversely impact aquatic insects which are at the base of the food chain, reduce channel capacity, and decrease the overall quality of lakes, streams, and wetlands.
  • Damage on Wetland Mitigation Sites: Studies show sediment deposition of less than 0.1 inch results in a 60-90% decrease in wetland seed germination from new seedlings or from wetland seed banks. Decreased species diversity is also a result of sediment deposition, with less desirable species often becoming prevalent.

What Costs Are Associated With Construction Site Erosion?

Flooding: Sediment accumulation reduces storm water conveyance and storage functions of streams, wetlands, storm sewers, detention basins, highway drainage ditches, and floodplains, which can result in flooding. Over time, municipal and industrial water supply reservoirs lose storage capacity, navigable channels must continually be dredged, and the cost of filtering and disposing of muddy water in preparation for human or industrial use increases.

  • Safety and Nuisance Issues: Sediment on roadways creates potential safety issues and is a nuisance.
  • Increased Construction Costs: Uncontrolled erosion and sediment deposition increases construction costs. Sediment fills drainage channels, detention basins and storm sewers and plugs culverts and storm drainage systems, which then require frequent and costly maintenance. Construction sites that are not effectively stabilized can cause serious erosion problems that require re-grading. Damage to new plantings on mitigation sites or other areas often require replanting at a significant cost.
  • Negative Public Perception: The public often observes muddy water leaving a construction site. Erosion and sediment control measures may cost more up-front, but in the long-term are cost-effective. Failure to comply with local, state, or federal law may result in significant penalties. Environmental compliance problems can adversely affect public perception.

What Can Be Done To Control Soil Erosion And Provide Sediment Control?

Preventative Action: Numerous studies show that it is more cost effective and institutionally feasible to develop measures to prevent or reduce pollutants in storm water during new development than to correct problems caused by these pollutants later.

Best Management Practices: Implementing appropriate best management practices on construction sites protects and improves local surface water resources and community infrastructure investments.

Incorporate Soil Erosion and Sediment Control as an Integral Part of Construction: Planning for soil erosion and sediment control should be considered as important as any other component of the development process. Proper implementation and maintenance of planned practices will assure that costs incurred will be offset by economic, environmental and other benefits.

Minimize Erosion

Stage construction.

  • Schedule projects so clearing and grading are done during the time of minimum erosion potential.
  • Clear only areas essential for construction.
  • Locate potential non-point pollutant sources away from steep slopes, water bodies, and critical areas.
  • Route construction traffic to avoid existing or newly planted vegetation.
  • Protect natural vegetation with fencing, tree armoring, and retaining walls or tree walls.
  • Stockpile soil and reapply to revegetate soil.
  • Cover of stabilize topsoil stockpiles.
  • Use wind erosion controls.
  • Intercept runoff above disturbed slopes and convey it to a permanent channel or storm drain.
  • On long or steep, disturbed, or man-made slopes, construct benches, terraces, or ditches at regular intervals to intercept runoff.
  • Use retaining walls and check dams.
  • Provide linings for urban runoff conveyance channels.
  • Seed and fertilize.
  • Use seeding and mulch/mats, sodding, and wildflower cover.

Control Sediment

Use filter fabric fence. Filter fabric fence is available from many manufacturers and in several mesh sizes. Sediment is filtered out as urban runoff flows through the fabric. Such fences should be used only where there is sheet flow (i.e., no concentrated flow), and the maximum drainage area to the fence should be 0.5 acre or less per 100 feet of fence. Filter fabric fences have a useful life of approximately 6 to 12 months.

Use straw bale barrier. A straw bale barrier is a row of anchored straw bales that detain and filter urban runoff. Straw bales are less effective than filter fabric, which can usually be used in place of straw bales. However, straw bales have been effectively used as temporary check dams in channels. As with filter fabric fences, straw bale barriers should be used only where there is sheet flow. The maximum drainage area to the barrier should be 0.25 acre or less per 100 feet of barrier. The useful life of straw bales is approximately 3 months.

Protect inlets using a barrier placed around a storm drain drop inlet, which traps sediment before it enters the storm sewer system. Filter fabric, straw bales, gravel, or sand bags are often used for inlet protection. Use sediment basins, sediment traps, and vegetated filter strips. Prepare a construction site exit area using filter cloth covered with gravel to collect mud, gravel, and sediment from vehicles’ wheels.

For Additional Information:

If you have questions call the Storm Water Program Manager at 401-841-1790.

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