ABSTRACT
The grade control structures are frequently adopted in the Mountain Rivers and streams to prevent severe bed degradation and channel incision. These structures are constructed as a staircaselike sequence of transverse weirs or bed sills. Due to the plunging jets over structure crests, scour holes are generated downstream of the weirs (see Fig. 1). Once the local scour depth exceeds the embedded depth of the structure foundation, the structure itself and the function of grade-control system will fail. Therefore, accurate estimation of maximum (equilibrium) scour depth downstream of grade-control structures is necessary to ensure the safety of the structures. In this study, the related studies of local scour downstream of staircase-like weirs are reviewed, 5 important empirical scour equations for predicting equilibrium scour depth downstream of grade-control weirs are selected and evaluated. The evaluation process were established using the database formulated based on the equilibrium scour depth values (308 laboratory experimental data) reported in the previous literature. Several performance indicators, i.e. coefficient of determination, mean relative deviation, and under-prediction/over-prediction errors, were adopted and calculated to establish the ranking of the equations. The results show that the method proposed by Marion et al. (2006) was found to be the most accurate of the equations evaluated and is recommended for design use.
