Components, systems and materials › Bridge components › Drainage spout
Drainage spout
What it is
A drainage spout is a short pipe through a bridge deck with a grated inlet at the kerb that carries rainwater off the riding surface.
Where it is used
Bridge and flyover decks, usually along the low kerb line, at regular spacing and upstream of expansion joints.
How it works
Camber and longitudinal slope send water to the kerb channel, where it enters the grating and drops through the spout. On flyovers in cities, spouts connect to downpipes that lead to the street drainage so water does not fall onto roads or footpaths below.
Types
- Free-fall spouts on river bridges
- spouts connected to collector pipes and downpipes
- slot drains for wide decks
Materials
Cast iron, ductile iron, galvanised steel or HDPE bodies; cast iron or steel gratings; clamps and brackets for downpipes.
Spacing comes from design rainfall intensity, the deck area drained and the capacity of each inlet. The outlet must project well below the deck soffit so water does not run back along the concrete and stain or corrode it. Inlets just upstream of expansion joints stop water reaching bearings.
Installation and QA steps
- Fix spouts in the deck formwork at the correct level, slightly below the wearing surface.
- Concrete and protect the spout from blockage.
- Fit gratings flush with the surface.
- Connect downpipes where required.
- Clean before and during the monsoon.
- Blocked inlets causing ponding and aquaplaning
- spouts too short so water stains and corrodes girders and bearings
- discharge onto traffic, footpaths or railway lines below
- wearing course laid over the inlets
Related
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