What is the recommended spacing for road gullies?

Generally 30 to 50 meters, adjusted based on road gradient, width, and local rainfall intensity (Clause 4.2).

When should a trapped gully be used?

A trap is required when the gully discharges into a combined sewer or a foul sewer to prevent gas escape. It is not needed for a separate surface water drain (Clause 5.1).

What is the minimum depth for a water seal in a trapped gully?

The water seal should have a minimum depth of 75 mm (Clause 5.2.1).

How frequently should road gullies be maintained?

They should be cleaned before the start of the monsoon and at least twice during the monsoon period, with more frequency in areas prone to heavy silt or debris (Clause 8.1).

IS 7740

: 1985

Code of practice for construction and maintenance of road gullies

CurrentSpecializedCode of PracticeBIMWater Resources · Public Health Engineering

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This code of practice provides guidelines for the construction and maintenance of road gullies used for collecting surface water from road surfaces. It covers their location, spacing, types (trapped and untrapped), construction details, and essential maintenance procedures to ensure effective road drainage.

Code of practice for construction and maintenance of road gullies

Quick Reference Values

Typical spacing of gullies on urban roads30 to 50 m

Minimum depth of water seal in trapped gullies75 mm

Minimum depth for silt collection below pipe invert225 mm

Recommended slope of connecting pipe1 in 100 to 1 in 150

Typical depression of gully grating below road surface10 to 20 mm

Practical Notes

Ensure the gully grating is set slightly below the surrounding road surface (10-20mm) to effectively capture runoff and prevent ponding.

Regular cleaning and desilting, especially before and during monsoon season, are critical to prevent blockages and localized flooding.

Use trapped gullies only when connecting to a combined or foul sewer system to prevent escape of sewer gases; untrapped gullies are sufficient for dedicated surface water drains.