As a function of their design, the storm drainage system must be protected from an influx of sedimentation. To measure this, a Low-Impact Development (LID) ESC methods are used which consist of the following. – All LIDs must be identified on drawings
– LID protection must be spelled out in ESC plan
– Discharge Rate must be determined
LID systems typically rely on filtering runoff through soil and vegetation. This means to decrease the runoff flow, landscaping and other design practices must be implemented. Such LID practices may include the following.
Absorbent Landscapes: A thicker less-compacted soil supports the vegetation which tends to maximize the holding potential of the water runoff.
Boiretention Facilities: Like rain gardens, they tend to be found alongside commercial buildings to remove contaminants in the runoff.
Bioswales: Landscaping that reduces the silt and pollutants in the runoff. This is soil vegetation along gently sloping surfaces.
Green Roofs: A roof partially or completely covered in vegetation. Sometimes includes drainage and barrier systems.
Rain Gardens: Mostly used in single family lots, the plants and soil remove the contaminants in the runoff.
Recycling & Reuse: These are cisterns or underground storage tanks that hold excess runoff to be used for other purposes.
All these practices will help reduce the sediments, slow down the runoff, and catch excess water during a precipitation event. To employ such practices, they must be part of the construction process that identifies which method or series of methods should be incorporated into the construction site.
Identification of Construction Methods
It may be that one or more LID method is used in the construction site. Each stage of the construction must be considered separately. LID Installed Last: The preferred method is that once the area of upstream catchment is created and stabilized, the LID is then installed. Isolation Methods: If the upstream areas are not stabilized, then the LIDs must be protected using measures such as sod, sand, aggregate, or poly sheeting that incorporates a barrier. This should protect the infrastructure from sediment buildup.
Protection that is Structurally Designed
These are temporary or permanent controls that either prevent sediment buildup or create conditions where the sediment can be easily removed. This is an extra control used in conjunction with good ESC practices such as the following.
– Diversion of Runon with the LID(s)
– Silt Fencing around the LID(s)
– Awareness & Inspection of LID(s)
Once the proper construction method has been identified, the right ESC methods must be used to protect the LID. For any ESC practice to work with an LID, they must match in terms of function. This is defined in Section 5 of the City of Calgary Water Resources publication.
Keep in mind that LIDs are sensitive to sediment buildup and must be addressed in a reasonable amount of time. This is why the proper ESC practices must be used in conjunction with the LID to ensure maximum results. Such ESC practices must offer greater protection than 2 t/ha/yr.
Tag: Sediment, Erosion, Control, developments, low impact, stormwater
