ESTIMATION OF SCOUR AT BRIDGE PIERS.

The conventional Indian practice for estimation of pier scour using Inglis formula viz. maximum pier scour D//s//m equals 2 times the flow depth according to Lacey formula 'd//L' has various limitations, as discussed. The shortcomings of current Roads Congress and Railway practices can be overcome by adopting the Cumulative Scour Approach which gives total pier scour by addition of individual scour depths (i) due to river constriction by guide bunds (resulting in looseness factor becoming 1 or less), (ii) due to unequal discharge distribution, and (iii) due to pier obstruction. This approach is applicable to bridges on alluvial rivers with sandy bed provided with conventional design of guide banks and waterway. Cumulative scour approach is rational and capable of further improvement as and when more data becomes available.