Between the time they are graded and permanently stabilized, constructed slopes are vulnerable to erosion. A fill slope or un-stabilized cut may be required to carry the runoff down the slope to prevent erosion from taking place. This is where a temporary slope drain using a conduit, over-side drain, or flexible tubing may be needed running from the top to bottom of the slope itself.
Implementation
The drains can be constructed using a variety of materials, from corrugated metal culvert pipe to open top over-side drains. The area of the drainage will determine the size of the drain itself. A simple formula can be used to determine the diameter of the pipe needed for the temporary drain.
Maximum Contributing Drainage Area to Minimum Pipe Diameter (Inside)
– 0.2 ha = 300 mm
– 0.6 ha = 450 mm
– 1.0 ha = 530 mm
– 1.4 ha = 600 mm
– 2.0 ha = 760 mm
Building the Drain
ou’ll need to build a temporary diversion ditch and berm along the top of the fill slope or cut to direct or collect the runoff. A minimum of 0.3 m higher than the top of the slope will be needed for the diversion berm over the inlet of the slope drain.
Place the drains on compacted or undisturbed soil at the proper locations according to the ESC drawing. Make sure the drain extends beyond the toe of the slope and dissipate the energy of the flow using gravel, a concrete slash pad, or riprap at the downslope outlet of all slope drains. You will need to build an inflow apron structure, erosion-resistant ditch block, or interceptor channel to add slope to the drain inlet. It will need to be sloped slightly towards the slope drain. An A-T pipe configuration at the inlet will help drainage and reduce undermining or scouring. A major cause of drain failure is scouring and seepage.
The slope drain will need an inlet berm or barrier with a minimum 0.45 cm soil cover above the top of the pipe. Be sure the barrier or berm is compacted soil of 150 mm soil lifts minimum. The side slopes must not exceed 2H:1V gradient. Use vegetation or other erosion control system to line the storm drain after it is built. Install more scour protection, such as riprap, at the inlet.
Using hold-down grommets, anchor stakes, or other approved materials to secure the slope drains so they do not move.
Inspection & Maintenance
Inspect all drains and berms at least once per week or after heavy runoff from precipitation or snowmelt. Repair any damage quickly and remove all accumulated sediment from the slope drain. Install additional anchors is the drain has moved. Once a permanent drainage system has been constructed, remove all temporary berms and channels and establish vegetation cover.
Tag: Sediment, Erosion, runoff, berms, channels, drainage, vegetation, drains, permanent, precipitation, repair, slope, system, temporary
