Variation of water and sediment in the Yellow River and the strategy for harnessing its lower reaches

Variation of the oncoming water and sediment conditions in the Lower Yellow River such as much less frequency of occurrence of floods and long duration of drying up of the river flow in recent years led to a decrease in flood conveyance capacity of the main channel. As a result, water level during a medium flood in 1996 was very high that vast floodplain was inundated land great damage was observed. Aimed at flood prevention, utilization of water resource and transportation of sediment load in the lower Yellow River, regulation of sediment on perennial basis should be adopted as a guide in the operational mode of the Xiaolangdi reservoir, that is: retention of sediment in the reservoir in dry or normal years and disposal of the sediment concentratedly in flood periods in wet years so that hyperconcentrated flow may be created to form narrow and deep channels in replacement of the wandering wide and shallow river in reaches upstream Gaocun. With the narrow and deep channel, sediment load may be conveyed all the way through the lower Yellow River by the hyperconcentrated flow. Comparison and analysis of the results of computation for different schemes indicate that the benefit of the proposed scheme is significant in reduction of sedimentation, saving water required for sediment transportation and making more reasonable use of the Yellow River water resource. In order to reduce the damage during medium floods, as a transitional measure, the small dikes used to be built on the floodplain for protection of the crops from inundation should be recovered to reduce the inundation losses. River training should be strengthened in reaches upstream Gaocun to control the bank erosion during the release of clear water in the initial periods of operation of the Xiaolangdi reservoir So as to form relatively a narrow channel and wide floodplain.