Effect of Groyne on Reducing Coastal Erosion in River Bend

Groynes are constructed in arch or straight streams in order to protect river banks and reduce their erosion. Local scour at the nose of groynes is one of the most important issues in designing groynes that is created due to the contraction of the flow section and presence of strong vortexes. In this study, experiments were carried out on series of straight groynes located in a laboratory channel bend with different flow discharges and different angles under clear water scour condition. The maximum scour depths and sedimentation (deposition) area between them were measured and compared with each other. In order to assess the flow pattern, velocity measurement around the groynes was done with an Electromagnetic velocitymeter. Results showed that the maximum scour depth was around the normal groyne and for the three normal, repelling and attracting arrangements, the first groyne had the maximum scour depth while this depth was minimum at the last one. Also for the normal and repelling groynes, for a given ratio of velocity to the critical velocity, the sedimentation area between the first and second groynes was greater than that between the second and third groynes and for the attracting groynes, the inverse trend was confirmed. For various angles of groynes, while increasing the ratio of velocity to the critical velocity, the deposition between the groynes was reduced.