Why do wetland mitigation areas need silt fencing?

Wetland Mitigation

Wetland Mitigation

Everyone involved with wetland mitigation should understand what the protected resource is and where it is located. Often silt fencing is needed to filter and safe keep water within the designated area. Both contractor and property owners are responsible for complying with the Permit by Notification for the creation of wetlands. The Huron Township LDFA has been involved for years in wetland mitigation as well as wetland banks for businesses that need to relocate wetlands on LDFA properties. 

Erosion is the loosening and movement of soil particles from its original location by water, wind or gravity. Turbidity, which is the mixing of sediment with surface water, degrades water quality and sediment deposition is harmful to wetland resources. Sedimentation is the process by which sediment is relocated or deposited. Erosion results in turbidity when soil particles are carried into water bodies.

Soil particles carry phosphorus, a nutrient that can cause algae blooms and water quality degradation. Suspended sediments can damage fish gills while deposited sediment can smother fish eggs and small aquatic animals (invertebrates).The bed of a lake or pond that has been coated with sediment may be more susceptible to the growth of some aquatic weeds, such as milfoil.

Sediment deposition can cause wetlands to lose function and value. Sedimentation of wetlands and surface waters is a violation. By installing erosion controls, the potential for sedimentation, siltation, or turbidity is virtually eliminated, the resource is protected and so is the property interests.

When you see markings  in a Huron Township LDFA property with ribbons or flagging or installation of orange construction fencing, that means construction is underway.  Owners may also identify and mark particular trees and shrubs that they want protected. Heavy machinery must be kept well away from trees to avoid compacting their roots; otherwise, they will die a few years later. Trees roots can also be smothered if excess fill is deposited around them.

Wide buffer strips of undisturbed vegetation along stream and lakeshores protect water quality. If you will be working in wetlands or near surface waters, you will probably need silt fence, straw bales and grass seed or conservation mix. Some good places to check are feed stores, hardware stores, landscapers and contractor supply houses. It is not always easy to find hay or straw during late winter and early spring. It may also be expensive during those times of the year.

Plan ahead and purchase a supply early and keep it under a tarp. Prefabricated silt fences that come with attached posts are also convenient. They usually have a colored stripe a certain distance from the edge to indicate the depth to which it needs to be dug in to the ground.

Before any soil is disturbed, an erosion control barrier needs to be  installed. The barrier can be a silt fence, a row of staked straw bales or both. In some areas, you may need a wire mesh to support the silt fence. Both silt fence and hay bales must be trenched into the ground to be effective.

Most groups plan earth-moving activities early enough in the year so that you can re-vegetate the site by October 15. Plan to mulch disturbed areas before the winter if construction is delayed past October 15. This will protect bare soil from spring runoff.

Machinery must not be allowed to cross streams. Major damage to stream banks occurs when heavy equipment is run in stream channels. The group should install a filter barrier on the down slope side of the a hilly construction area. This barrier can be a silt fence, an embedded hay bale barrier, or a combination of the two. A silt fence is better at filtering out soil from water, but is easily pushed over by construction equipment. Hay bales do not filter dirty water as well as silt fence, but are more rugged in the field.

Hay bales and silt fence work only when they are installed properly and maintained. Erosion control technology is continually evolving. Innovative technologies, such as filter socks and fiber matrices provide options to silt fence and hay bales as well as alternatives may be used for challenging areas.

During construction, straw mulch should be used on disturbed soil. The purpose of mulch is to prevent rain from striking the soil directly. It is the force of raindrops striking the soil that causes a lot of erosion. Keeping the soil covered can prevent most erosion. Mulch provides the added benefit of discouraging weeds from becoming established in the disturbed soils.

Inspection for erosion control barriers should be done frequently and after each rainfall. If there is muddy water leaving the project site, the erosion controls are not working.

Contractors use mulch hay liberally on disturbed soil during the construction period to avoid creating an erosion problem. Hay mulch is the cheapest and most effective way to protect the soil. Construct suitable runoff and erosion control structures. Consult with an engineer for sites with very erodible soils, steep slopes, natural springs and seeps, and spring runoff channels and streams. New seeding should be covered with mulch hay or straw. Mulch should be applied at a quantity of two bales per 1,000 square feet.

After construction, when the earthmoving is completed, replanting of the area is important. Owners should replant native trees shrubs, and groundcover. These species are generally better at taking up pollutants and nutrients in storm water runoff. A mix of creeping red fescue and Kentucky bluegrass is a good choice for lawns. The same mix would not be a good choice for stabilizing a road shoulder, berm, or cut bank that they don’t plan to mow.

Owners should be extremely careful when using fertilizers near streams, lakes and ponds and not apply fertilizer before a storm. Visit the shoreland website for restrictions on fertilizer use: www.des.nh.gov/cspa.

Silt fencing should be replaced when water no longer is allowed to filter through it. If the project is finished after October 15,  grass seed and mulch should be spread on the site with a thick layer of hay or straw. The following spring, you may need to mulch again retain moisture and prevent the seed from washing away.


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