Catch water drains in hill roads

A catch water drain (catch drain) is a lined or unlined open channel excavated on the hillside above the top of a cut slope, roughly parallel to the road, which intercepts the surface runoff from the upper catchment before it reaches the road.

Role and necessity

• Protects the cut slope from erosion and from saturation by running water; the slope remains stable, which reduces landslides.
• Reduces the load on the side drain and cross-drainage structures, because they only have to carry the water from the road and the cut face.
• Prevents water from entering tension cracks at the top of the slope, which could trigger slips.
• Keeps the pavement and formation dry, protecting the subgrade strength and the road life.
• Diverts the water safely to the nearest natural stream or cross-drain through a stable outlet.

Practical details (IRC:SP:48 / NRS 2070)

• Placed about 5-10 m (at least 3-5 m) beyond the crest of the cut.
• Trapezoidal or rectangular, lined with stone masonry or concrete in soft soil; bed gradient about 1-6% so that it neither silts nor scours.
• The excavated material is placed as a bund on the downhill (road) side of the drain, and the outlets are protected by chutes.