Assessment of Regime Equations for Predicting General Scour

There are various equations for predicting general scour that are presented in technical papers, design guidelines, and design manuals. Three such equations are the regime equations which were originally published by Gerald Lacey in 1930, Thomas Blench in 1969, and C.R. Neill in 1973. These regime equations are included in a United States Bureau of Reclamation (USBR) technical guideline titled, “Computing Degradation and Local Scour”, 1984; National Resources Conservation Service (NRCS), National Engineering Handbook (NEH) Part 654-Technical Supplement 14B, Scour Calculations, 2007; and in various local agency design manuals. However, the regime equations as presented in these publications are different in form than the equations in the original reference documents and as a result provide different calculated scour depths. The paper examines the differences between the equations as reported in the design guidelines/manuals and the equations as originally documented, summarizes limitations of the equations, and provides examples to compare the variation in scour depth when applying different forms of the equations.