ESSENTIAL REQUIREMENTS FOR THE MINOR BRIDGES AND CULVERTS, AND CONSIDERATIONS OF THE ECONOMY.

As for as the cost of construction of type of culverts and bridges is concerned, generally the governing factor for the selection of type of bridge the exact arrangement economically suitable for a particular case depends upon the natural conditions e.g . foundations and the specified requirements like width , loading appearance, waterway,time of construction, difficulties in the form work etc etc Looking to various factors involved in the selection of type, experience is invaluable in deciding the type of common use of the structure, suitable for the purpose.Considerations of economy require that small culverts ,in contrast with relatively larger structures across defined channels,need not be designed normally to function with adequate clearance for passing floating matter .The depth of culvert should be small and it does not matter if the opening stops appreciably below the formation level of the road .Indeed ,it is correct to leave it in that position and let it function even with its inlet submerged.This makes it possible to design low abutments , supporting an arch ,or a slab ,or alternatively,to use the round pipes or square box barrels.In case the masonry abutments supporting arches or slabs are designed for culverts functioning under "head",bed pavement must be provided .And ,in all cases , including the pipe and box culverts, adequate provision must be made at the exit against erosion by designing curtain walls .Where the exit is a free overall ,a suitable cistern and baffle wall must be added for the dissipation of energy and stilling of the ensuring current.The high headwalls should not be provided for retaining deep over-fills ,instead ,the length of the culvert should be increased suitably so that the road embankment,with its natural side slopes ,is accommodated without high retaining head walls .