ABSTRACT
Local scour at the toe of transverse structure like groundsill is inevitable. Therefore, selecting suitable bed protection length is necessitated to protect channel bed from scouring. An array of 1:50 scaled low-head groundsill models was installed in a flume to explore the effectiveness of riprap protection lengths and riprap sizes. Results of the study indicate that riprap at the toe of a groundsill does not eliminate the impact force of plunge flow completely. The length of riprap protection helps cultivate and maintain a hydraulic venue that is primarily dictated by riprap sizes provided that riprap protection extended downstream long enough to cope with diverse plunge flows’ trajectories. Otherwise, the effectiveness of scour control will be minimal regardless the sizes of riprap. A dimensionless relationship is developed from this study to help estimate the geometry of local scour, which in turns helps select the riprap protection lengths and riprap sizes.
