Abutments and spur dikes
Spur dikes are usually designed to protect the banks or to provide enough flow depth for navigation purposes. Abutments can be placed on one bank or symmetrically on both banks of a waterway. An abutment can be protected by an adjacent bed protection to prevent the formation of a scour hole in the direct vicinity of the abutment. In general, a distinction can be made between streamlined and blunt or sharp-nosed abutments. There are wing-wall abutments of several complicated shapes, including straight wing-wall abutments with a T-head or L-head, curved wing-wall abutments shaped like a hockey-stick, or an inverted hockey stick. In scale models a vertical-wall abutment is sometimes schematised as a vertical plate with a vertical head. For local scour near abutments and bridge piers the interaction between the wake vortices is important. The process of local scour around abutments can be divided into several phases: initial phase, development phase, stabilisation phase and equilibrium phase.