Author(s): Xiaozhou Xiong; Bruce W. Melville; Heide Friedrich
Keywords: Butment scour; Contraction length; Bed-morphology; Maximum scour depth; Surface velocity field
Abstract: This study investigates the effect of contraction length on abutment scour morphology, the surface velocity field and maximum scour depth. A series of experiments wereconducted in a tilting flume (45-m long and 1. 5-m wide) with uniform coarse sand (d50 = 0. 84-mm). The models representing the long and short contractions wereequivalent to vertical-wall abutments. The results of four groups of experiments are presented (two experiments per group), covering eight possible combinations of varying contraction ratio, contraction length and flow intensity. An ultrasonic depth-sounder, a Flow Tracker Acoustic Doppler Velocimeter and Particle Tracking Velocimetry (PTV) were used to obtain equilibrium scour depths, detailed bed-scour contours around the abutment and two-dimensional surface velocity fields. Results show that contraction length has only a small effect on maximum scour depth and equilibrium bed morphologies. In addition, the surface velocity fields for both initial plane bed and equilibrium scour condition are similar for long and short contractions. The need for additional experiments, investigating approach channel geometry and geotechnical stability, is emphasized.