Water and sediment characteristics and theirscouring and silting law in the three rivers of Ningbo

The water and sediment characteristic in Yongjiang River is described qualitatively from the point of view of changes in water runoff,tidal volume and sediment concentration in the history,then the principles of riverbed evolution in Fenghua River,Yaojiang River and Yongjiang River is illuminated.The river bed was stable previously,but the construction of Yaojiang barrage in 1959 and the sea wall in Zhenhai in 1975 caused marked siltation all over the river that making the river adjust to the change in water flow characteristic,and it took many years to recover balance.With the rapid development of economy,many projects are constructed on Yongjiang River such as reservoirs,bridges,wharfs and so on,which making siltation occur slowly in Yongjiang River especially the side beach.Fenghua River is also in the station of tempered siltation.The downstream reach of barrage of Yaojiang River is in the station of siltation due to the weak characteristic of flow when the barrage is closed.The research of the principle of riverbed evolution of Yongjiang River can improve the theory of riverbed evolution of the tidal estuaries and provide suggestions for siltation remove in the similar tidal estuaries.