Study On The Response Of Hydro-sediment Dynamics To Eco-friendly Structure

Revetments are important hydro-structure for rivers,lakes and sea,especially for the protection of estuarine and coastal engineering.The concept of eco-hydraulic engineering,which includes the design and application of eco-friendly structure in revetment construction,has attracted more and more attentions.It is of importance to study the design of different eco-friendly structures and the interactions between these structures and the hydro-sediment dynamics.In this study,the response characteristics and reasons of different eco-friendly structures to hydro-sediment dynamics and the associated depositional processes are studied investigated.Three different types of eco-friendly structures units are designed according to diversion structure,habitat suitability and the permeability of water,named as they are strong permeable type,medium permeable type and weak permeable type.The permeability is 33%,20% and 14% respectively for the three types of the structural units.The arrangement of the side holes are the same between the weak and the middle-permeable type,while the difference lies in the permeability of the top holes indicating 16% and 49%,respectively.The permeability of the top holes of the strong pervious type and the middle-pervious type are the same,while the those of the side holes are 25% and 5%,respectively.Both the flume experiments and Flow-3D numerical simulation were carried out,to study the effects of the eco-friendly structures on the over-current capacity,sedimentcatching capacity,flexible vegetation and biological adaptability.The following innovations are recognized:(1)The lateral permeable area of the eco-friendly structure plays a leading role in the flow velocities inside the structure and the total pervious area plays a dominant role in the turbulent intensity inside the structure.The smaller the permeable area on the side of the eco-friendly structure,the greater the deceleration rate of water flow in the structure.The deceleration rate of weakly permeable and medium permeable structures is 26?29% higher than that of strong permeable structures.The smaller the total permeable area of the eco-friendly structure,the smaller the intensity of turbulence in the structure.The turbulence intensity of the weakly permeable structure is about 17%to 34% lower than that of the medium and strongly permeable structures.Strongly permeable structures with a larger side permeable area have a greater deceleration and energy dissipation rate as the distance from the front surface is greater;while weakly permeable and medium permeable structures with a smaller permeable area,the greater the distance from the front surface.Deceleration and energy dissipation first increase and then change smoothly.(2)The permeable area of the eco-friendly structure determines the sediment trap in the structures.The stronger the vortex near the bottom of the structure,the more uneven the distribution of the sediments.The permeable area of the lateral surface of the eco-friendly structure affects the concentration of suspended sediment inside the structure.The average suspended sediment concentration inside the structure of the strong permeable structure is 21?28% higher than that of the medium permeable and weak permeable structures.The permeable area of the top surface controls the amount of deposition in the structure.The deposition volume of the impermeable structure is14% lower than that of the medium permeable structure.At the same time,as the permeable area of the eco-friendly structure is larger,the effects of the vortex near the bottome layer on the sediment deposition is more remarkable.In addition,there are differences in the shapes of the depositional patterns,such as V-shaped and crescentshaped,respectively.(3)Under the combined effects of eco-friendly structures and flexible vegetations,the internal structure exhibits a stronger deceleration,turbulence,and sediment traping.The eco-friendly structure and the flexible vegetation are spaced apart,and the average flow velocity is 0.30 m/s and the suspended sediment concentration is 0.16 g/L.Under the experimental conditions,the strong,medium,and weakly permeable structures with flexible vegetation are compared with those without vegetations.The vegetations promotes the internal deceleration rate by 3?12%,reduces the turbulence intensity by6?14%,and facilitates the deposition by 20?28%.At the same time,the permeability of the eco-friendly structure directly affects the habitat of large benthic organisms.When the flow velocity is lower than 0.35 m/s,the medium permeable structure is suitable for the survival of Eriocheir sinensis(90±5 g).