Water-sediment regulation by the Xiaolangdi Reservoir and the response of the Lower Yellow River

Xiaolangdi Reservoir is located at the key position for controlling water-sediment of the Lower Yellow River.Since its operation in Oct.1999,large quantity of sediment especially coarse sediment has deposited in the reservoir.Density flow becomes the main way to discharge sediment to the downstream.During 2002 to 2004,three times of artificial regulation of water and sediment were carried out.Meanwhile,tremendous changes of the water-sediment condition entering into the Lower Yellow River have happened.These changes include low sediment concentration,fine sediment size,gentle flood peak,decrease of runoff in flood season,increase of runoff in non-flood season,etc.Under such water-sediment conditions,the corresponding responses happened in the Lower Yellow River such as continuous erosion,increase of bank-full discharge,decrease of width-to-depth ratio,coarser bed materials,and change of river regime.