Street Gullies and Kerb Inlets (Bushakle): Draining City Roads Without Flooding

After a summer cloudburst in Tbilisi, the streets that flood are rarely the ones with too little pipe. They are the ones where water can't get into the pipe: blocked gratings, gullies spaced too far apart, or inlets set a few centimetres above the road. The street gully — known on Georgian sites as a *bushakle* — is the part of the storm system that does this job. It is small and cheap, and it is easy to get wrong. These notes cover how to choose and specify gullies and kerb inlets for city roads. They are general engineering guidance, to be read against the project's drainage design and municipal requirements.

EN 124 defines classes by location, not by the size of the vehicle you expect:

• C250 – gullies in the kerb-side channel, extending at most 0.5 m into the carriageway and 0.2 m into the footway.
• D400 – anywhere in the running carriageway, including gullies placed away from the kerb, at junctions, or in car parks where trucks turn.

If a gully may end up under a wheel track after future road widening or re-marking, specify D400.

• Place gullies upstream of pedestrian crossings and junctions, so water is collected before people cross.
• Always put one at low points (sag curves). Use a double gully if the catchment is large.
• On steep grades, water runs past gratings, so reduce spacing and choose gratings with diagonal or transverse bars.
• A common starting point is about 20–40 m between gullies, set by the drainage designer from rainfall intensity, gradient and road width.

• Bar orientation: diagonal or transverse bars are safer for cyclists and catch water better on slopes.
• Hinged and lockable gratings: stop theft and make cleaning safe.
• Silt trap or bucket: catches sand and leaves before they reach the collector, which matters in hillside districts.
• Material: ductile iron for C250/D400 roads. Composite or plastic only for pedestrian and private areas.

1. Set the frame 5–10 mm below the adjacent asphalt so water flows in. Never set it proud of the surface.
2. Bed the frame on high-strength mortar or a concrete collar, not on loose bricks.
3. Connect the gully to the collector with a properly sloped lead (often DN 150–200) and a trap where required.
4. Clean all gullies before handover. Building waste is the main cause of early blockages.

State type, class, size, connection and level: *"Combined street gully (grating + kerb inlet), ductile iron EN 124 C250, grating 400×600 mm with hinged lockable lid and silt bucket, outlet DN 200 to storm collector, frame set 5–10 mm below finished asphalt on high-strength bedding mortar."* For gullies inside the carriageway, change the class to D400.

GON supplied manholes and rain-water gratings for Tbilisi road works on Akaki Tsereteli Avenue, Tskneti Highway, Kakheti Highway and 9 April Street. Our range includes the bushakle street gully C250 and D400 square gratings in 600, 700 and 710 mm sizes, plus the Tbilisi-pattern D400 grating.

Related products: Drainage & stormwater · Kerb manhole cover C250 · Manholes & covers · HDPE corrugated pipe

Send the road drawing to sales@gon.ge and we'll mark the gully type and class for each inlet. You can also call +995 595 818 800. GON has offices in Tbilisi and Batumi.