Discharge Capacity
Similarly, asymmetrical trapezoidal sections may require the discharge to be spread over more than one pan.
Where it is necessary to increase the penetration outlet to more than one pan of a trapezoidal profile, the side curbs can be tapered from the pan to the height of the rib as shown in Penetration Discharge.
Profile | Pitch | Max. catchment |
Corrugate Symmetrical trapezoidal 5 & 6 rib trapezoidal or trough | 8° 4° 3° | 5 m² 10 m² 20 m² |
The discharge capacity is limited by the capacity of one side of the penetration flashing (half the total catchment). For Example, the maximum length of run for a penetration 1m wide using corrugate is 10m.
Example 1
Five-rib trapezoidal with a 1 m wide penetration 15 m below the apex in a 100 mm/hr DRI area.
Width | Length | DRI | Catchment per side |
1 | 15 | 100 | 7.5 m² |
Result—OK to Use
Example 2
Corrugate with a 1.2 m penetration 10 m below the apex in a 140 mm/hr DRI.
Width | Length | DRI | Catchment per side |
1.2 | 10 | 140 | 8.4 m² |
Result—Exceeds table. Discharge over two crests as per drawing 6.1.6B
If the catchment area is greater, the discharge is spread over two or more pans as shown in Penetration Discharge.
Penetration Discharge
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