Permanent stabilization techniques typically include restoration of disturbed soil by seeding and planting, and placement of other erosion control measures such as rip rap or erosion control blankets.
Frequently water movement in streams and along stream banks could be very fast requiring robust permanent erosion controls. Slope instability such as scouring or sliding can also undermine adjacent trail sections. Additionally, bridge scour may occur when bridges constrict the cross section of the stream it, increasing the velocity of the flow through the bridge. The increase in velocity can break up and erode the ground at or near the structural elements of the bridge, creating safety and water quality issues. Structural elements such as piers, abutments, and wing walls should be protected from scour to prevent bridge failures. Stream velocities and depth will determine the level of protection required for disturbed banks upstream and downstream of crossings and the existing channel geometry (width, channel slope and cross slope) will help determine which permanent stabilization technique is appropriate.
Permanent stabilization techniques include the following:
- Restore disturbed wetlands, streambanks, or streams using native plants appropriate to the desired established conditions including wetland and stream type. Restoration of plants will help control erosion post-construction. Laying back steep streambanks will help prevent further loss of bank due to erosion. Planting and seeding disturbed wetland or streams adjacent to trails or boardwalks should be implemented with native plugs and seeds appropriate to the post-construction conditions such as depth of water and expected saturation duration. Seed species, rates (ounces/acre), extent and the need for a cover crop is to be determined by a landscape architect or other qualified professional.
- Installation of vegetation in conjunction with erosion control matting, geogrid fabrics, and rip rap at the toe of the slope can help prevent future erosion.
- Rip rap to be used only at toe of slope where needed. Consider coir logs as alternative for aesthetic purposes.
- Installation of rock veins, j hooks, bentway weirs or other in stream structures can serve as grade control structures that direct stream flows perpendicular to the structure and reduce stresses on failing stream banks.
- All bridge structural members should be adequately protected again sheer stresses resulting from a 100-year peak flow through the channel being crossed. Adequate protection measures can be determined by conducting a stream flow analysis to determine peak flow, velocity and sheer stresses through the crossing.
Permanent erosion control measures are available in a variety of construction methods depending on the situation. These methods are intended to prevent scouring from flowing water bodies or erosion of steep slopes from storm events.