Though the Flood-Control-Projects along Yantze River and Jialing River in Chongqing may well improve the urban traffic and construction

it may change the river hydrodynamic characters.There may be two consequences

one is to reduce the size of cross section and the other is to change the river shape

such as the curvature radius.The phenomena of the local backwater and velocity variety are obvious

which result in some problems for the navigation: sediment

transport and so on.In this paper

the study object is the Flood-Control-Projects and Yangtse River and Jialing River

and the aim is to study the influence of the Flood-Control-Projects on the hydrodynamic state of the two rivers.Using the numerical technique

with the two rivers hydrodynamic model the flow field's change of river after completion of Flood-Control-Projects is simulated and the reasons caused by the change are analyzed.