ANALYSIS OF RIVER MOUTH BEHAVIOR CHANGE BY USING AERIAL PHOTOGRAPHS

Abstract

The morphology change of the Nanakita River mouth is monitored by the utilization of aerial photographs colleted since 1990 to 2002. The method for detecting land and water area in the photos is investigated by the application of image analysis in order to reduce time consuming for manual digitization. From the color information in the aerial photo, hue and lightness are appropriately used to detect land and water area. The criterion can be acquired by normal distribution function. The photo. analysis results show that the Nanakita River mouth behavior trends to stabilize and has less development of the left sand bar in the recent years. In this study, the influence from seaside is examined. Breaking of wave is calculated from the wave ray model then longshore sediment transport near the river mouth can be computed from CERC formula. The computed results show the decreasing of longshore sediment transport corresponding to the river mouth behavior. For this reason changing of longshore sediment is supposed to be one of the significant factors for stabilization and diminishing of left sand bar in the recent year.