Construction BMP Guide: C201 Grass Lined Channels
Grass lined channels are typically used in roadside ditches, channels at property boundaries, outlets for diversions, and other channels and drainage ditches in low areas. Grass lined channels proved a vegetative lining for conveyance of runoff to help prevent the transport of sediment and erosion.
*The contents of this guide are to provide a general overview only. It is the users responsibility to ensure all BMPs utilized on their project meet the requirements of their state and local jurisdictions.
Grass Lined Channel Installation:
- Install vegetated channels and hydroseed with bonded fiber matrix before major earthwork occurs
- Vegetation should be well established (> 50% cover of all seeded areas after 3 months of active growth) before water is allowed to flow into the ditch.
- Install erosion control blankets over the hydroseed with channels that will have high flows.
- If vegetation cannot be established before allowing water into the ditch, sod should be installed in the bottom of the ditch in lieu of hydro mulch and blankets
- Locate channels where they can conform to the topography and other features such as roads.
- Use natural drainage systems to the greatest extent possible.
- Avoid sharp changes in alignment or bends and changes in grade.
- Do not reshape the landscape to fit the drainage channel.
- Do not subject the grass-lined channel to sedimentation from disturbed areas- Used sediment trapping BMPs upstream of the channel
- V-shaped grass channels generally apply where the quantity of water is small, such as in short reaches along roadsides. The V-shaped cross section is least desirable because it is difficult to stabilize the bottom where velocities may be high.
- Trapezoidal grass channels are used where runoff volumes are large and slope is low so that velocities are nonerosive to vegetated linings.
- Subsurface drainage or riprap channel bottoms may be necessary on sites that are subject to prolonged wet conditions due to long-duration flows or a high water table.
- Provide outlet protection at culvert ends and at channel intersections.
- Construct channels a minimum of 0.3 feet larger around the periphery to allow for soil bulking during seedbed preparations and sod buildup
Grass Lined Channel Maintenance:
- During the establishment period, check grass-lined channels after every rainfall.
- After grass is established, periodically check the channel; check it after every heavy rainfall event. Immediately make repairs.
- Check the channel outlet and all road crossings for bank stability and evidence of piping or scour holes.
- Remove all significant sediment accumulations to maintain the designed carrying capacity.