Objective
The objective of Perimeter Control Measures is to define formal site perimeter protection along downslope boundaries which may be subject to erosion and sediment transfers beyond the site margins and pose a risk of sediment introduction affecting the drainage system or natural areas.
Measures
Standard Silt Fencing
Silt fencing (PDF) is a pre-fabricated geotextile fabric with supporting stakes. It is installed to intercept and detain transported sediment via the impoundment of flowing water behind the fence fabric, creating a depositional environment. Silt fencing is not a filtration device and should never be installed in situations where concentrated or channelized flows will develop. It is critical that silt fencing is properly installed as per the manufacturer’s specifications, with the lower flap of the geotextile fabric “keyed in”. Sediment accumulations exceeding a third of the fabric height must be removed.
Wire Backed Silt Fencing
Similar to standard silt fencing, wire backed silt fencing includes a geotextile fabric and support stakes; however, the geotextile is further supported by a wire mesh to provide additional support and integrity for locations anticipated to receive significant sediment loads between maintenance events.
Wood Mulch Berm
On sites with limited topographic relief, wood grindings generated during site clearing activities may provide a beneficial erosion control product subject to their use in areas without prolonged exposure to standing water or seepage zones. The use of wood mulch may include the construction of temporary berms along site perimeters to detain site runoff and promote settling of suspended sediments. Wood mulch berms should be a minimum of 1 metre wide at the base and 300 to 500 millimetres in height depending on site conditions/grades.
Fiber Logs Barriers
Sediment logs may include manufactured straw wattles, composted wood mulch berms or wood fiber logs. Sediment logs require installation as per manufacturer’s specifications which typically include “intimate contact” with the substrate to prevent surface runoff from breaching or bypassing the Best Management Practices. Typically, fiber log barriers are most suitable for perimeter control measures on small lots or low gradient surfaces.