Temporal evolution of scouring downstream of a trapezoidal piano key weir

Abstract

ABSTRACT This study experimentally investigated the temporal evolution of the scour parameters downstream of a trapezoidal piano key weir. The densimetric Froude number (Fr d50) in the range of 0.39–0.57 and the relative vertical distance of the sediment bed level to the weir toe (Δz/P) in the range of 0.025–0.5 were taken into consideration. In general, with an increase in Fr d50, the scouring rate, maximum scour depth, scour hole area and scour hole volume enhanced over time. The increases in the scour parameters were greater at the initial stages of the tests. About 87, 80, 65 and 70% of the maximum scour depth, weir toe scour, scour hole area and scour hole volume occurred within the first 20% of the durations of the tests, respectively. Any increase in Fr d50 and Δz/P augmented the scour depth at the weir toe. The results also indicated that the distance of maximum scour depth from the weir increased for greater values of Δz/P and Fr d50. The amounts of scour downstream of the outlet keys were greater than those downstream of the inlet keys. The trend of variations of the longitudinal bed profiles remained nearly unchanged over time. New equations were developed to predict the temporal variations of scour parameters, with acceptable accuracy.