SPECIFICATION
Grate Pattern and Hydraulic Intake Area
How slot width and pattern affect intake capacity, and when a ductile iron grate outperforms a narrow stainless slot.
Knowledge Centre - Specification · 4 min read
Slot width and pattern determine intake area
The intake area of a channel grating is the total open area through which surface water can enter the channel body. A wider slot or a denser pattern of openings increases intake area per metre of channel run.
A single narrow slot produces the most discreet sightline but admits the least water per unit length. A double slot roughly doubles the open area. A patterned grate with multiple openings can exceed both, depending on the geometry.
Single slot vs double slot as a flow trade-off
The single slot grating suits locations where the drain line should read as a hairline - residential driveways, pool surrounds and landscaped plazas where flow volumes are moderate and sightline matters most.
Where catchment area or rainfall intensity pushes the required intake beyond what a single slot can admit, the double slot grating serves the same channel body with approximately twice the open area. The trade-off is a wider visible slot in the paving surface.
When ductile iron outperforms a narrow stainless slot
Ductile iron gratings use a broader, open pattern that maximises intake area per metre. In locations with high flow volumes - road-edge interception, service yards and basement ramps - a ductile iron grate admits more water than either stainless slot variant.
The additional intake area matters most where undersizing the inlet would cause surface flooding before the channel body reaches its hydraulic capacity. Specifying ductile iron in these locations prevents the grating from being the bottleneck.