BEACH CHANGES CAUSED BY CONSTRUCTION OF RIVER MOUTH JETTIES AND AN ARTIFICIAL REEF TO REDUCE SAND DEPOSITION IN RIVER MOUTH

Abstract

Beach changes due to the elongation of river mouth jetties around the mouth of the Arakawa and Kinotodainichi Rivers in Niigata Prefecture are investigated. Topographic surveys off the river mouths were carried out seven times from 1988 to 1999. Since southward longshore sand transport prevails at this river mouth, south beach was gradually eroded after the extension of the jetties, whereas sand accumulated at the river mouth. The occurrence of scouring around the artificial reef and jetties, which was predicted by the previous study based on the topographic surveys, is confirmed in the real data. The effectiveness of an artificial reef constructed off the mouth of the Kinito-dainichi River to prevent sand deposition inside the river mouth is verified.