Objective
The objective of On-Site Waste Management is to collect and convey site runoff to detention facilities in a manner that mitigates the risk of potential channel erosion or sediment transport within the drainage features.
Measures
Interceptor Ditch / Swales
Interceptor ditches or swales (PDF) should be constructed with slopes constructed at a maximum grade of 2:1 and stabilized with the use of temporary disturbed surface protection Best Management Practices to mitigate rill erosion of the ditch banks themselves. Ditch inverts should be constructed with a flat bottom and include rock mulch check dams installed at spacing dictated by the gradient of the channel.
To reduce flow velocities and mitigate channelized scour, check dams should be installed such that the top of the downstream check dam is equivalent to the base of the next upstream check dam to create a stepped channel profile with 0% gradient between the check dams. Where ditch gradients exceed 5%, the invert of the ditch and lower one-third of the banks should be armoured with clear fractured rock mulch sized to the dimensions and flow capacity of the temporary ditch.
Slope Drains
Temporary slope drains (PDF) may include the construction of a polyethylene-lined flume, a rock-armoured channel, or the temporary installation of a flexible “Big-O” pipe to convey flows down a slope. Flows should be captured at least 1 metre back from the slope inflection point and carried over the slope break to prevent scour. The base of the slope drains must be constructed/stabilized to protect from potentially high energy flows at the point of confluence with downstream drainage facilities.
Adaptive Water Management
Adaptive water management (PDF) measures may include the construction of temporary sumps and hard piping, or construction of temporary drainage ditches or swales as discussed above. Opportunities for the construction of infiltration trenches to manage minor seepages and convey drainage via permeable media (i.e. coarse sand or rock) may also provide suitable adaptive water management. Adaptive water management also encompasses measures aimed at intercepting and diverting surface runoff around temporary stockpiles or construction materials which may be placed on paved surfaces. The establishment of temporary sandbag berms located on the upslope margin of stockpiled materials is an effective measure to divert surface runoff around the base of potentially erodible materials to preclude entrainment and transport to stormwater inlet structures.