琵琶湖岸,萩の浜の海浜過程に関する研究

Abstract

To preserve natural lake shore environment along Lake Biwa, the beach processes should beinvestigated. Haginohama is one of the beautiful sandy beaches in the west side of the lake. Inthis paper, beach processes of Haginohama are studied in terms of coastal engineering to clarifythe present situation of the beach and to predict beach changes.Wave hindcasting was carried out for a period of 32 years between 1950 and 1981 to find long-term wave action on Haginohama beach. The Gumbel extremal distribution is employed to esti-mate the most probable wave heights and their return periods. Characteristics of beach sedimentare considered, and predominant directions of littoral sand drift are found along the beach. Nume-rical calcualtion was made to estimate the predominant directions of littoral sand drift in terms oflongshore wave energy flux for every five years of the period. This agrees with the predominantdirections estimated by the characteristics of beach sediment. A one-dimensional analysis of beachchange was employed to predict beach changes in several conditons of sediment sources and shorestructures. From the view point of long-term beach change, there exists a deposition area by thecentral part of Haginohama beach, but the effective waves to the beach was caused by the typhoonswhich passed through near the lake.