Reduction of time-dependent scour around piers using collars

In the present study, the effect of collar on temporal scour depth variation at the base of a collar-protected circular pier was investigated. Experimental results revealed that a collar performs efficiently by reducing the rate of temporal scour depth variation around the pier. The efficiency of a collar, for different diameters and elevations, has been studied through flume experiments under clear-water scour condition. Analysis of obtained experimental results indicates that a collar performs efficiently and reduces maximum equilibrium scour at (undisturbed) bed-level. Further, the observations of the study revealed that the effectiveness of a collar increases with increase in collar diameter and decreases with the elevation of collar. Finally an empirical equation has been proposed to compute the time-dependent scour depth at the front of the collar -protected piers. The proposed equation has been validated and proven to be applicable to a wide range of variables under the effect of non-contraction flow. A sensitivity analysis has been done and it indicates that the collar diameter and its elevation are the most influencing parameters.