Abstract:Flow structure will become more complex when there are large scale congeries in the river.Based on the flume experiment study

the three dimensional flow structure of river channel under the influence of congeries was studied

and the velocity was measured using the Acoustic Doppler Velocimeter(ADV).The analyses of the velocity around the congeries at different plane showed that congeries led to water block at theupstream of congeries

and then waterfall.The direction of the maximum longitudinal velocity from the congeries gradually turns to the right bank and the bottom of the riverbed in the vertical

and then rise and return to the natural state at the downstream of congeries.The main stream was in hydraulic jump state affected by the shrinkage of the river section around the congeries.Under the influence of the flow area of the river section cutted down and the inertia of the flow

the maximum velocity occured in the downstream position of the congeries.Transverse velocity appeared positive and negative values in a certain depth at the section of congeries.Water flows to the left bank in the upper layer of the depth

and to the right bank in the lower layer.It occured to reverse flow in the upper and lower layers.At the same time

this phenomena also appeared in the vertical velocity.It appeared spiral flow in the test section.Du to the influence of the congeries

the flow from the surface to the bed was in different width contraction.Besides

the spiral flow interactiving with the hydraulic jump made the flow in a complicated three dimensionalstate.