Many offshore structures such as breakwater and seawall have been designed and constructed mainly to get calmness by reducing huge wave force and to prevent urban area from tidal and tsunami attack.In 1985, the current development policy was revised and a new long-term port construction and maintenance policy called “Port toward the 21st century” was established to promote comprehensive development of port and harbor facilities. According to the new policy, two construction projects, Wakayama Marina City project and Sun-port Takamatsu project, were conducted, where breakwaters and seawalls were planed and designed to be widely opened to citizens. In the projects, three essential subjects had to be considered and solved in the design: design for harmonization of water amenity-oriented functions and safety, design for stability of the facilities with water amenity-oriented functions against wave force, and design for maintenance of the facilities.
　Regarding to the first subject, a new design concept of offshore structures to be widely opened to citizens was proposed by considering a waterline as a “coordinated boundary” dividing into sea area and human society, in which natural beauty and natural threat can be recognized through “their vision”. And based on this concept, several techniques in order to secure water amenity-oriented functions and safety are shown. The reliability of the proposed design is verified by the evaluation results on Sun-port Takamatsu project.
　Regarding to the second subject, new types of breakwater and seawall for the two projects were developed and the design procedure on their stability calculation was proposed for preliminary filed test procedure and evaluation procedure on wave reflection and propagation.
　Regarding to the last subject, a new maintenance design and procedure was proposed based on the experiences in Sun-port Takamatsu project and accumulated case histories.Based on the series of investigations mentioned above, systematization of designs of offshore structures with water amenity-oriented functions is proposed and evaluated in this article.