A gully is a drainage chamber set into paving that collects rainwater from a road, footpath or plot and discharges it to the sewer or to a watercourse; it is closed with a grating or cover.
Types of gully
| Type | Location | Characteristic |
|---|---|---|
| Road gully | In the carriageway, along the channel | Grating sits flush in the surface |
| Kerb gully | Behind the kerb face | Water enters through an opening in the kerb, no grating in the footway |
| Channel gully | In a paved or dished channel | Takes concentrated run-off |
| Yard gully | Driveway, parking area, garden | Often plastic, with fixed or removable silt bucket |
Materials: cast iron (strong and heavy, suitable for traffic loads), concrete, and plastic (light, for gardens and driveways).
Silt trap and trap seal
Most gullies have a silt trap at the bottom: a bucket below the outlet where sand, leaves and grit settle instead of washing into the sewer. Many also have a trap seal — a water seal that holds back sewer air. In a long dry spell that seal evaporates, and the street starts to smell.
Practical tips
- Empty the silt trap yearly — a full trap stops draining and causes puddles. Put a bucket underneath, lift out the basket, empty it.
- Falls matter most — lay paving with roughly 1 to 2 per cent fall (1 to 2 cm per metre) towards the gully. Any less and water stands.
- Set the grating slightly low — about 5 mm below the surrounding paving, so water actually runs in.
- Connection pipe — use at least a 110 mm PVC pipe to the sewer, laid to a fall.
- Do not assume rainwater may go to the foul sewer — many authorities now require rainwater to soak away on the plot for new build and alterations. Check local rules before connecting.
- Never wash paint, oil or mortar residue into a gully — it goes straight into the sewer or watercourse.
Related terms
- Channel drain
- Dished channel
- Rainwater drainage
- Rodding eye
- Infiltration
- Surface water drainage
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