Approaching flow to bed forms and hydraulic structures can be appeared as accelerating or decelerating in rivers and natural channels. Knowledge of incipient motion in non-uniform flows can greatly influence on scouring and resistance to flow in rivers. The objective of this research is to study the turbulent flow characteristics on the threshold of motion in non-uniform flows. The experiments were carried out in Hydraulic Modeling laboratory of Nanyang Technological university in a 14(m) long, 0.6(m) wide and 0.6(m) deep flume using three sets of uniform sediment with median grain sizes of (D 50 =1.8, 1.3 0.8 mm) and 8 slopes of 0.007, 0.009, 0.0125 0.015 under non-uniform flows.
