ABSTRACT
When designing a new bridge there are occasions when it is desirable to optimise the hydraulic performance, perhaps because only a very small afflux can be tolerated without causing flooding upstream. This can be achieved partly by using slender, round-nosed piers (or eliminating them altogether), spillthrough rather than vertical abutments, and by avoiding skewed or eccentric openings. However, sometimes it may be necessary to adopt additional measures to improve the flow through the bridge, such as when economic or other considerations result in a less than ideal location and alignment for the crossing, or when the channel is braided or has a tendency to migrate. Under these circumstances some form of 'improvement works' may be needed to increase hydraulic efficiency at the design discharge. I f possible these works should be incorporated at the design stage; it is usually less satisfactory and more expensive to add them at a later date.
