Evaluation of Procedures for Calculating General Scour

Regime equations formulated by Gerald Lacey, Thomas Blench, and C. R. Neill may be used to predict general scour in alluvial channels of each procedure and offers findings on the different results obtained from the two procedures. The regime equations calculate an average scoured depth, the depth measured between the water surface elevation and the average scoured bed elevation, for a channel considered to have attained equilibrium. The depth commonly used in design of waterway structures is the depth of scour, the depth measured between the unscoured bed elevation and the scoured bed elevation, which can be determined by subtracting the depth of flow from the scoured depth. An alternate procedure that has been suggested and is being used to determine the depth of scour is to multiply the average scoured depth, as calculated from the regime equations, by an empirical factor. The two procedures do not result in the same depth of scour. This paper provides an evaluation of each procedure and presents findings on the results obtained from the two procedures.