Study On Mechanism And Effect Of Flow Control And Aggradation For Permeable Pile Dike

Since boundary of the Lower Yellow River bed varies with the flow conditions, main channel of the stream continually shrank and flood control becomes rather difficult. It is insistent and important to study and develop novel control techniques of the river flow.Permeable pile dike is an important method for stream control in river restoration or construction, and is of some marked advantages including deep groundwork, large strength, simple construction, little emergency, easy maintenance, effective control on the flow trend and increasing the sedimentation. In 1960s, it was tested to build permeable pile dike at some places along the Lower Yellow River. However, some stakes were destroyed by flood due to technique limit then, and efficiency was decreased. To improve the river reconstruction technique, it is necessary to investigate mechanism and effect of flow control and aggradation for permeable pile dike.Efficiency of permeable pile dike is closely related to water-sand ratio in upstream flow, direction of the coming flow and seepage rate. This paper investigates mechanism and effect of flow control and aggradation using hydraulic modeling and theoretical analysis. It is shown that suitable seepage rate can help aggradation and suitable coming flow direction can help to govern the flow trend. Three kinds of permeable pile dikes with different seepage rate are tested, and effect of flow control is basically the same with the spur dike,. The test shows that when flow rate is greater than 3000 mVs, the effective downstream length may reach 2.2~~3.5 km and increases with the flow rate. For different upstream conditions, thickness of sediment in the permeable pile dike region may reach 0.67 m, and largest thickness is nearly 1.9 m, and largest width reaches 1 km. Scouring depth before the permeable pile dike reaches 20 m and the value increase with the upstream angle and flow rate of the coming flow. The present research shows that the permeable pile dike is rather valuable in the Yellow River restoration.