Cross Drainage
Whenever streams have to cross the roadway, facility for cross drainage 1s to beprovided. Also often the water from the side drain is taken across by these cross drain in order to divert the water away from the road, to a water course or valley The cross drainage structures commonly in use are culverts and small bridgesWhen a small stream crosses a road with a linear waterway less than about six meter, the cross drainage structure provided is called culvert: for higher values of linear waterway, the structure is called a bridge.
The common types of culverts in use are
Slab culvert
Box culvert
Arch culvert
Pipe culvert
slab culverts RcC slab is placed over abutments made of masonry and the span isgenerally limited to 3 metre.
Box culvert of square or rectangular shapes is mads ofRCC.
Arch culvert is generaly built using brick or stone masonry, plain cement concrete
may also be used.
Pipe culverts ot minimum diameter 75 cm and made of steel or prefabricated RCC is used when the discharge is low.
Various types of bridges are in use: the choice is based on severalconsiderations including the span. RCC and steel bridges are commonly constructed these days
On less important roads, in order to reduce the construction cost of cross drainage structures, sometimes submersible bridges or cause ways are constructed. During the floods the water will flow over the road. The total period interruption to traffic has however to be kept as low as possible, not exceeding about 15 days in a year.
