Abstract: The flow velocity of river is easily affected by deposit. In this research, the 3-D flow velocity in the vicinity of deposit was observed by ADV through flume experiment, and the cross-sectional 3-D velocity distribution in the upstream channel nearby the deposit was researched by controlling the flow rate. Results suggest that under the same flow rate, velocity is affected by the shape of deposit. As the distance to the riverbed reduces, the curve of velocity distribution in u direction (the direction of flow) becomes steeper, and the peak of velocity in v direction (pointing to the side of the right bank) and w direction (vertical to riverbed) is closer to the projection line of the deposit in cross-section.The curve of velocity in v direction is a straight line approaching zero value in natural conditions; while in the presence of deposit, the straight line transformed into a parabola that reflects the increase of peak velocity and the decrease of velocity in two sides as the distance to riverbed gets smaller. The curve of velocity in w direction in the vicinity of riverbed displays a “spoon” shape; while as the distance to riverbed increases, the “spoon” shape disappears. Moreover, as flow rate increases, the velocity in u direction increases at the same height, and the transverse velocity distribution gets more uneven and the curve becomes steeper. The angle θ between the velocity in u direction and the velocity in v direction reaches the minimum when the distance to the left bank (with deposit) is about half of the deposit radius. As the distance to the left bank grows, the value of θ increases, and then returns to the natural value 90° until the distance to left bank reaches 45 cm.The research results provide technical support for river protection and treatment.

Key words: deposit, 3-D velocity, fixed bed, lateral velocity distribution, flume experiment