A Simple Equation for Stable Coastline between Groins and Between T-Head Groins by taking into account diffracted Wave

Coastal protection planning using groin requires information on erosion and sedimentation that will occur at the protected coastal segment. An easy and practical yet accurate calculation method is needed, so that the planning cost is not too expensive. This research developed a method of stable coastline calculation between groin, which includes erosion and sedimentation that occur during the process leading to stable coastline geometry. The governing equation is formulated using the principle of mass conservation where the volume of sedimentation is equal to the volume of erosion, whereas the boundary condition is that stable coastline is oriented perpendicular toward the wave forming it. Therefore, there are two stable coastline orientation, i.e. stable coastline formed by the incoming wave and stable coastline formed by diffracted wave. Using this method, a very simple and easy to use stable coastline equation is obtained. The equation is formulated for a coastline with groin protector and a coastline with T-Head groin protector. A comparative study was done for the efficiency between the two structures.Stable coastline that was produced is very simple and easy to use. The result of another study stated that for the similar construction volume, T-Head groin provides a better protection.