Great changes on the Lower Yellow River channel since 2000 and future prospective

With the construction of large hydropower projects on the upper and middle reaches,the development of soilwater conservation and irrigation projects,the probability that a big flood event will occur and flood peak discharges have been greatly reduced. It is unnecessary to widen the lower-reach river to allow floodplain inundation for flood peaks reduction. In recent years,there is a major breakthrough in the understandings of the mechanism and capacity of the sediment transport in the narrow and deep channel of the Yellow River. Lower-reach channel has huge flood discharge and sediment transport capacity,which points out the future direction of harnessing the river. After the reconstruction of Sanmenxia Reservoir and the operational mode of storing clear water and releasing muddy waterto reduce deposition, non-siltation has already been achieved for the channel upstream of Huayuankou. After the operation of Xiaolangdi Reservoir for 13 years,great changes have taken place in the lower-reach channel with maximum longitudinal water surface elevation reduction of 1. 0- 2. 2 meters,and the bankfull discharge has been increased dramatically. But the wandering reaches are still wide,shallow,scatter and ill-conditioned,and they need to be regulated at both banks to form a stable, deep and narrow channel. Through multi-year sediment regulation of valley type of reservoirs like Xiaolangdi,the combinations of flow and sediment entering the lower-reach can be optimized,and the reservoir can be used for a long time. Sediment should be managed to be released when discharge is greater than 3 000 m3/ s,and it should be transported through the regulated new channel to sea. By using this approach,the river bed will not be elevated by deposition,and the beneficial use of the reservoir will be significantly increased too.