Effect of regulation of flow and sediment by the Xiaolangdi Reservoir on deposition in the lower Yellow River

The Xiaolangdi dam is an important hydroproject in controlling flow and sediment entering the lower Yellow River. It has been started to be operated since 1999, and has important effect on mitigating deposition in the lower Yellow River. The flood that occurred in 2003 in the middle Yellow River was a floods with the longest flooding duration and the biggest volume of flow since 1981. It came mainly from the Weihe River, one of the tributaries of the Yellow River, It was composed of four flood peaks at Tongguan hydrometric gauging Station, of which the maximum peak is 4,350 m(3.)s(-1) with a sediment concentration peak of 260 kg(.)m(-3). To fight against the flood, the Xiaolangdi dam was operated in an abnormal manner, resulted in an apparent change in the hydrograph of the flood when it entered the lower Yellow River with its peak reduced to as low as about 2,500 m(3.)s(-1), which would have been around 5,000 m(3.)s(-1)-6,000 m(3.)s(-1) if without such a special operation. The statistics indicated that the flattened flood led to 0.145 billion ton of sediment eroded from the channel, consequently the flooded floodplain area was 10 greatly reduced by 16,667 km(2). The research provides a good foundation for determination of the operation of the Xiaolangdi dam.