1999 Volume 27 Pages 305-314
In Japan, lakeshore vegetation has been decreasing in many places. Lakeshore erosion due to wind waves is one of the main reasons. Recent study reveals critical wave condition for creation of the stable lakeshore. The artificial floating island (AFI) is a breakwater to control wave condition, which functions for production of vegetation habitat and improvement of water quality as well. AFI was experimentally installed at Shimanami Area in Lake Kasumigaura in 1998 in order to protect lakeshore and vegetation against waves. In this area lakeshore vegetation has been rapidly decreasing due to wave action. AFI is designed to attenuate significant wave height from 64 cm to 30 cm. As a result, lakeshore vegetation area has expanded 3.4% after 1-year period experiment. Annual wave energy behind AFI becomes half of that in the offshore. However, wave intrusion from lateral sides is significant in AFI and it causes lateral erosion of lakeshore. Installation of a breakwater made of riprap is recommended at lateral side in order to decrease wave reflection by covering the vertical seawall.
