Flow Characteristics And Local Bed Deformation Around A Notched Groyne And Its Engineering Application

Groyne which can protect riverbank and harness water channels is widely used in hydraulic engineering.But the scour hole would be appeared around the head of groyne.The scour hole may lead to the destruction of groyne.To avoid these,a new type of groyne which is a notched groyne is studied in this paper.The notched groyne adds a horizontal interface based on traditional groyne.It can reduce the depth of scour hole around the head of groyne.And there would be more flow structure.That different configurations of notch impact on characteristics of hydrodynamics,erosion and deposition of sediment is studied by physical model experiment and numerical simulation.And the notched groyne is applied to practical engineering.(1)There are two recirculation zones behind near-shore block and off-shore block.Separation of boundary layer occurs when the water flow bypasses the far-shore head and towards-shore head of off-shore block and the head of near-shore block.Due to the notch,mean velocity around the head of groyne is less than that of traditional groyne.The scope of downflow in front of notched groyne decreases.(2)When the position of notch is towards shore,the length of recirculation zone behind near-shore block decreases.While the length of recirculation zone behind off-shore block increases.The time average velocity of the zone around notch and far-shore head of off-shore block is almost same.The position of notch does not affect the division ratio of notch.The water flow which get through the notch is changed from deflecting to mainstream to deflecting to bank.With the increase of length of notch,the length of recirculation zone behind near-shore block and off-shore block decreases.And the time average velocity of the zone around notch and far-shore head of off-shore block reduces.The division ratio of notch is raised.(3)The setting of notch has an efficient effect on the reduction of the scour hole around the head of groyne and the scale of downstream scour hole.The scour hole appears around downstream of the notch,the head of off-shore block and the towards-shore head of off-shore block.When the position of notch is towards shore.The maximum depth of scour hole decreases.The maximum depth of scour hole around the far-shore head is reduced and the maximum depth of scour hole around the towards-shore head first increases and then decreases.When the position of notch is too near the shore,the scour hole around the notch extends towards the shore.When the length of notch increases.The maximum depth of scour hole decreases.The maximum depth of scour hole around the far-shore head decreases.The maximum depth of scour holes around the other two head of notched groyne also decrease.When the length of notch is less than one-sixth of the length of notched groyne,the scour holes around notch and downstream of notch are linked together.(4)When the notched groyne is designed.The position of notch should be avoided too close to the heel of the groyne or the head of the groyne.The relationship between the length of riverbank which the notched groyne protects and the safety of the notched groyne is considered synthetically.Protection measures should be proposed to avoid erosion damage.(5)The design parameters of notch groyne are decided based on the research results of characteristics of hydrodynamics,erosion and deposition of sediment of notched groyne.A notched groyne is applied to Min River South Bank.When the construction of the notch is on the first groyne.The velocity of the head of groyne has a 10%reduction.And the flow structure between first groyne and the second groyne has changed and the flow structure between the other groynes has no obvious difference.It is benefit to the safety of groyne structure.It can also protect the bank.