Response of the distributary channel of the Huanghe River estuary to water and sediment discharge regulation in 2007

The water and sediment discharge regulation(WSDR) project,which has been performed since 2002 before flood season every year,is of great significance to the river management in China.Until 2007,six experiments have been fulfilled to evaluate the effect of the project on the natural environment.To fill the gap of investigations,a study on flood and suspended sediment transportation and channel changing along the distributary channel of the Huanghe(Yellow) River was conducted during the WSDR project period in 2007.The lower channel was scoured rapidly and the channel became unobstructed gradually several days after the flood peak water was discharged from the Xiaolangdi Reservoir.Within four days after the flood peak at 3 000 m3/s entered the distributary,the channel in the river mouth area was eroded quickly.Both the mean values of area and depth of the main channel were tripled,and the maximum flood carrying capacity increased to 5 500 m3/s or more.Then,the river channel was silted anew in a very short time after completion of the WSDR.Favored by the WSDR project,the river status in April 2008 became better than that of the year before.The adjustment ranges of main channel parameters were about 30%,10%,and 10% at sections C2,Q4,and Q7,respectively.The process of rapid erosion-deposition was more active 15 km away in the channel from the river mouth due to the marine influence.It is reasonable for discharging sediment at concentration peak from Xiaolangdi Reservoir at the end of the flood peak.As a result,the sediment peak reached the river mouth about two days later than that of the water current.In addition,the WSDR project has improved the development of the estuarine wetland.Wetland vegetation planted along the river banks restrained the water flow as a strainer and improved the main channel stability.It is suggested to draw water at mean rate of 150 m3/s from the Huanghe River during flood periods,because at the rate the water in the wetland would be stored and replenished in balance.Moreover,we believe that cropland on the river shoal of the lower Huanghe River should be replaced by wetland.These activities should achieve the Huanghe River management strategy of "To concentrate flow to scour sediment,stabilize the main channel,and regulate water and sediment".