The main aim of this master thesis is the design of coastal structures as a part of the project for expanding and increasing the capacity of the existing Kostanj beach in Rijeka. The coastal structures that were analyzed here are the coastal wall that extends the existing coastal wall and the submerged breakwater. The introductory part of this study describes the environmental characteristic of the location, as well as the geographic and seismological features, which proved an insight into the situation in the field and facilitate a proper design of coastal structures. The theoretical preliminaries of the submerged breakwater are presented next, along with the wave deformations and their effects on the breakwaters, such as the wave overflow, runup, run-down, transmission and reflection. Within theoretical part, the coastal walls types and all the forces exerted on them are also discussed and presented. After the theoretical part, breakwater efficiency is examined by the computation model SWANONE [19], which computes the wave heights before and after the completion of the submerged breakwater. The breakwater is designed by the Van der Meer formula [18], whereas the coastal wall is designed according to EUROCOD 7 and 8, which define appropriate methodology for verifying the wall stability. Finally, the approximate costs are analyzed and the design drawings are given.