Effects of cut-off on Tongguan elevation in Dongluwan reach of Sanmenxia Reservoir area

The elevation of Tongguan plays a very important part in flood control for the downstream areas of Weihe River,as well as in multi-purpose benefits of the Sanmenxia Reservoir. Because of complexity of the factors influencing the Tongguan elevation,various management measures have been adopted for lowering this elevation. It follows from two natural cut-offs occurred between 1993 and 2001 at the Dongluwan section that each of the cut-offs has increased local slopes in the river,thus intensifying the actions of erosion in the upper river section and benefiting the elevation of Tongguan. There was one again a cut-off in the same section in October 2002. This cutoff would result,after the operating of the reservoir under decreased water and sediment level conditions for one flood period,in lowering the Tongguan elevation with a value of about 0.12 m according to the historic operational experience and existing data on erosion.