Essay On Road Drainage

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Drainage is the process of interception and removal of water from over, and under the vicinity of the road surface. Drainage can be surface (where water is conveyed on the road surface and drainage channels), or subsurface (water flows underneath the pavement structure).
Surface and subsurface drainage of roads critically affects their structural integrity, life and safety to users, and is thus important during highway design and construction. Road designs therefore have to provide efficient means for removal of this water; hence the need for road drainage designs.
Drainage facilities are required to protect the road against damage from surface and sub surface water. Traffic safety is also important as poor drainage can result in dangerous
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A = the catchment area in km2 HYDRAULIC DESIGN
Once the design runoff Q is determined, the next is the hydraulic design of drains. The side drainage and other structures are designed based on the principles of flow through open channels.
If Q is the quantity of surface water (m3/sec) to be removed by a side drainage and V is allowable velocity of flow (m/s) on the side drainage, the area of cross section A of the channel (m2) is found from the relation below: Q=A.V

The velocity of unlined channel must be high enough to prevent silting and it should not be too high as to cause erosion. The allowable velocity should be greater than one (1m/sec) for lined channel.
The slope S of the longitudinal drain of known or assumed cross section and depth of flow ,may determined by using Manning’s formula for the design value of velocity of flow V, roughness coefficient n and hydraulic radius R.

Manning’s Formula V=1/n*R2/3*S1/2

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