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Scour is a natural phenomenon in rivers caused by the erosive action of the flowing water on the bed and banks. Spur dikes are constructed across the flow to protect the bank from erosion by shifting of the river away from the bank. The spur dike undermines due to river-bed erosion and scouring, which is generally recognized as the main cause of spur dike failure. In this study, accuracy of existing equations for the computation of maximum scour depth has been checked with available data in the literature and data collected in the present study using graphical and statistical performance indices. Three new relationships are also proposed to estimate the maximum scour depth and maximum scour length upstream and downstream of spur dike. This new relationship for maximum scour depth is shown to perform better than other existing equations. [ABSTRACT FROM AUTHOR]

Spur dikes are river engineering structures that project from the bank of a stream at some angle to the main flow direction. They are principally used for river training and protection of the riverbank from erosion. A spur dike might be considered a form of macroscale boundary roughness, which produces a backwater effect upstream from the spur dike location. Despite this impact, spur dike design often proceeds without regard to the effect that the spur dike might have on the stream system. The work presented herein is on the backwater effect due to a single, vertical-walled spur dike. It is based on a momentum analysis in which the resistance offered by the spur dike is represented by a drag equation, for which the key parameter is the spur dike drag coefficient. Experimental data acquired for various configurations of a single spur dike within fixed-bed flumes have been used to calibrate and validate the proposed backwater model. The results show that the spur dike drag coefficient, hence the computed backwater effect, depends on the channel contraction caused by the spur dike, the degree of spur dike submergence, the aspect ratio of the spur dike, and the Froude number of the flow. [ABSTRACT FROM AUTHOR]