Stabilising Drainage Ditches
If you have a drainage channel or ditch which is suffering from poor maintenance there are a number of steps you can take to stabilise it.
Man-made drainage ditches with gently sloping bottoms can be stabilised with thick grass seeding and erosion control blankets. Natural drainage channels and creeks or streams cannot be cleared, re-routed, or otherwise altered. Moderately sloping ditches will likely require turf reinforcement mats and perhaps some rip rap if soils are silty. Steeply sloping ditches need heavier armoring with concrete, riprap, gabion baskets, retaining walls, or other approved products.
Ditches with silty soils are the most erodible and clay is the least erodible. Steeper ditches and those with highly erodible soils need more protection. Drainage ditch bank slopes must not exceed 2:1. If tractor mowers or other equipment will cross channels in the future, bank slopes must be 3:1 or flatter. The outlet must be installed, seeded, stabilised, and protected before the ditch receives incoming flows.
Seed ditches and install silt checks before excavating, filling, or grading uphill areas. Inspect, repair, and clean out sediment from upstream side of silt checks after each rainfall exceeding 1â„2 inch. Remove temporary silt checks after the site is stabilized and vegetation is established. Placing filter fabric under the ditch check during installation will make removal much easier. Stone bag silt checks are easiest to remove, and can be re-used.
Drainage ditches need temporary silt check dams to capture sediment and reduce ditch bottom down cutting. Silt dikes or dams can be made of rock, stone-filled bags, fiber rolls, or brush. They are only effective when the drainage area is 10 acres or less. Silt fencing and straw bales are not approved for use as silt check dams, and must not be used in drainage ditches that carry flowing water. Also, do not place silt checks in creeks or streams. Sediment must be intercepted before it reaches streams, lakes, rivers, or wetlands.
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