Stormwater Source Control Design Guidelines 2005 - Waterbucket

Stormwater Source Control Design Guidelines 2005Design, Construction and Maintenance ProcessConstruction Staging ChecklistProvide temporary fencing during construction if proposedinfiltration areas are in areas of natural vegetation, andrequire that vegetation remain in place.Ensure effective erosion control practices are in placeduring the construction period. If fine sediments aredeposited on infiltration areas by accident, remove thesurface crust prior to opening the infiltration facility.If possible, have stormwater outfalls bypass the proposedinfiltration area during construction.Do not place erosion control sediment traps in infiltrationareas. Only if absolutely necessary, build erosion controlsediment traps above infiltration areas, protecting theinfiltration soils with temporary cover of plastic, sand, orother mechanism that will capture all surface sedimentswithout compacting the infiltration area, and that can beremoved prior to opening the infiltration facility.When infiltration facilities involve the excavation of nativematerial, consider staging infiltration area excavation untilafter all adjacent construction is complete. Building tradeswill disturb and compact the native surface soils, but whenthey are removed for the final infiltration facilityconstruction, the compaction will also be removed.For infiltration facilities that involve excavation, ensure thatthe bottom and sides of infiltration excavations arescarified to remove glazing and improve infiltration.When infiltration facilities involve installation of growingmedium, ensure that layers of growing medium are tilledso that a transition of soil texture occurs. Do not compactbetween layers. Layers of different soil texture orcompaction can create perched water tables.Unvegetated infiltration areas that are subjected to heavyrainfall will set up a surface crust – even in sand. Althoughonly a new millimetres thick, the surface crust will impedeinfiltration. Any infiltration area, or growing medium, thatis left open to heavy rainfall, must be scarified prior toadding additional layers or opening for infiltration use.Cultivate in organic matter to the surface of growingmedium infiltration areas. The organic matter andassociated soil life will increase soil infiltration.Avoid the intrusion of road sands and construction trafficsediment into infiltration facilities, and pervious paving inparticular. Provide regular street sweeping of roads as apart of the erosion control system. After construction ,pervious paving should also be maintained by drysweeping at least twice annually.Greater Vancouver Sewerage & Drainage District115