This paper introduces the calculation for the channel full discharge and discharge capacity in the site after a bridge is set up,and the conclusion is that the structure does not influence the original channel full discharge,according to the practice application of the multi-span prestress concrete continuity plate bridge in Laolongkou Project.

As for the straight-labyrinth weir, the flow pattern character, the discharge capacity and its effecting fac.

Momentum transfer coefficient plays an important role in computing conveyance capacity, mean apparent shear stress on the vertical interface between main channel and flood plain, mean boundary shear stress on flood plains or in main channel respectively.

Aiming at the shortcoming,the paper adopts system dynamics method to study the conveyance capacity.

The rationality of flow-conveying ability of 4 000m~3/s in the main channel of the Lower Yellow River in the near future was discussed from the runoff condition of forming main channel,mobile-bed resistance,training works and flood control of the floodplain etc.