corresponding module before the crossing and the invert level under the crossing , which will become much deeper . ( Note : Swale module could sustain up to 20 T / m 2 ). For a crossing with an opening or width less than the width of the swale , which may lead to reduced capacity , modification of the road layers may be carried out by reducing the thickness of the binder coat . Designers must also consider the required 1 % gradient for marching field , hardscape or parking area which will discharge into the swale . The location and type of road curbs and scupper drain must be coordinated with the corresponding internal road and drainage plan .
No traffic should be allowed near swale alignment during construction . The excavator
should operate from the sides of the swale , and not on the base ( Figure 4.7 ).
Turfing
Grass planting and protective lining installation should be carried out according to the approved plan and method statement . The best planting period would be in the dry season and immediately after laying the sub-surface module and sand filling to avoid erosion and scouring ( Figure 4.8 ). If excavation is carried out during rainy season , covering using plastic sheets must be provided by the builder ( Figure 4.9 ). Watering the grass is required to stabilise the grass .
Construction at terraneous area a
The design process of BIOECODS at terraneous area , particularly as toe drain , must be considered with extra care as the stormwater velocity may be erosive . High-velocity stormwater calls for the provision of check dams or reinforcement matting along the swale as an energy dissipator , as proposed by MSMA ( DID , 2012 ). The use of chipping / gravels / boulders to replace the sand layer as the straining layer could be considered to increase the infiltration rate ( Figure 4.10 ). b
Figure 4.8 : Grass planting during dry season at ( a ) site A and ( b ) Site B
Figure 4.9 : Protective plastic covering ( Site A )
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