4.4 Erosion problems for structures adjacent to flowing water Bridge pier,abutments,bases for retaining walls, and footings for other structures adjacent to or located in flowing water must be located at a depth such that erosion or scour does not undercut the soil and cause a failure. Scour occurs principally during floods,but some scour occur at other times;in either case a scour-out pit or depression)in the stream bed may result. Scour is accelerated if the foundation creates channel obstruction. 4.4 Erosion problems for structures adjacent to flowing water ▪ Bridge pier, abutments, bases for retaining walls, and footings for other structures adjacent to or located in flowing water must be located at a depth such that erosion or scour does not undercut the soil and cause a failure. ▪ Scour occurs principally during floods, but some scour occur at other times; in either case a scour-out pit ( or depression) in the stream bed may result. ▪ Scour is accelerated if the foundation creates channel obstruction