Physical Model Experiment for Bank Regulations of the Lower Yellow River

Physical model experiment was carried out for Huayuankou to Jiahetan reach of the Lower Yellow River. This 103 km long reach is famous for being wandering, with strong depositions occurred often. It’s also called “suspended river” above ground. The braided reach is characterized by a distance of 5 to 20 km between the left and right levees, with a channel width of 1.0 to 3.5 km, and a longitudinal channel slope of 1.72% to 2.65%. The elevation difference between the floodplain and the main channel is relatively small, less than 2.0 m in the reach between Huayuankou and Gaocun. 

This reach is generally quite straight with a sinuosity coefficient of 1.15. In addition, the braided reach is composed of many wide and narrow stretches. In a wide stretch with a long stream length, there are numerous sand bars and complicated branches appearing at low water stages. This kind of planform results in flow diverging and frequent shifting of the main streamline. The channel bed is composed of fine sediment, with non-uniform size distribution ranging from 0.002 mm to 0.18 mm.

The physical model uses a horizontal scale of 1:800, vertical scale of 1:60. Fine residual of burnt coal ash from Zhengzhou Thermal Power Plant was used as the model sediment, with dry bulk density of 0.66 ~ 0.68 t/m³, wet bulk density of 2.1 t/m³. The initial condition of bathymetry was chosen as the field measured data in 2002. The inflow condition was provided by Yellow River Engineering Company of YRCC as a 15-year flow-sediment series from multi-year regulation rules of the Xiaolangdi Reservoir. The first five years was the initial operation period for Xiaolangdi Reservoir, only clear water was released to flush the sediment. The last 10 years was the multi-year sediment regulation when sediment was released only at certain right time during flood. In the proposed river training plans, 14 existing dikes will be still used, plus constructing of 250 new dikes. Each dike is around 1000 m long (200m of warping segment), with the top of the dike being 0.5 m higher than the floodplain. The distance between each dike is around 500 m to 800 m. The objective training width of the reach is set to be 600 m in general. At some curvature locations, this value was loosening to be 1000 m for flood protection purposes. 

The physical model results showed that with the regulation of Xiaolangdi Reservoir, around 80%-90% of the sediment can be regulated to be transported when the flow discharges are greater than 2,500 m³/s during flood season, especially for the year with abundant flow and sediment. The sediment transport ratio can be as high as 90% and above for the man-made flood with the construction of dikes.