Necessity of catch drain, causeway, EDS

i) Catch drain

A catch (intercepting) drain is a channel dug above the cut slope on the hill side. Its necessity:

• It intercepts runoff from the upslope catchment and carries it to a stream or a culvert before it reaches the road.
• It prevents erosion and gullying of the cut slope.
• It keeps the side drain from overflowing, and the slope and subgrade from becoming saturated, which reduces the chance of landslides.

ii) Causeway

A causeway is a low-level crossing built on the stream bed. Necessity:

• Where wide, shallow streams carry flow only during short monsoon floods, a bridge would be uneconomical.
• It is cheap, quick to build, and low in maintenance on low-traffic roads.
• It lets the flood flow over the road without damaging the embankment, which is protected by aprons and cut-off walls.

iii) Energy dissipating structure (EDS)

Needed where water flows with high velocity down steep slopes or leaves a culvert or drain on a steep outfall.

• It reduces the velocity and energy so that the flow does not scour the bed or undermine foundations.
• It prevents gully erosion and slides on the downstream slope.
• Examples: drop structure, stilling basin, rip-rap apron, check dams, baffle blocks.

iv) Sub-surface drainage

Needed where the water table is high, seepage emerges in cuttings or springs are present, or the subgrade soil is fine-grained.

• It lowers the water table and intercepts seepage, so the subgrade stays in the design moisture state (soaked CBR is not lost).
• It prevents pavement failure, pumping, frost heave and slope failures.
• It extends the life of the road and reduces maintenance cost.