Field measurements on the terrace topography, velocity distribution of the river currents as well as the grain size distributions were carried out at the mouth of the Yumizutani River flowing into Lake Biwa to investigate the formative mechanism of a river mouth terrace. On the basis of these field data, the action of river currents to sand movement offshore of the river mouth was incorporated into the contour-line-change model. A model for predicting the dynamically equilibrium topography under the action of waves and currents was developed. The impact of river mouth improvement such as the construction of jetties at the mouth was also tested using the present model.
