This study proposes a method for estimating river plume length from water levels and river discharge rates. A numerical model for coastal ocean dynamics was refined by comparing thermohaline fields calculated using the model with those measured off the mouth of the Sakawa River in Sagami Bay, Japan. The model successfully captured the reduction in salinity within the surface 1.0-m layer caused by riverine water transport. The simulated surface salinity maps revealed that the dynamic motions of the river plumes were primarily driven by one of the two diurnal occurrences of tidal current intensification. Regression analyses of the simulated results demonstrated that the river plume lengths were closely correlated with the water levels and river discharge rates, and that they could be accurately estimated from preceding river discharge rates under weak wind condition.

本研究提出了一种根据水位和河流流量估算河流羽流长度的方法。通过将使用模型计算的温盐场与日本相模湾佐川河口测量的温盐场进行比较，完善了沿海海洋动力学数值模型。该模型成功捕捉到了河流水输送导致地表 1.0 米层内盐度的降低。模拟的表面盐度图显示，河流羽流的动态运动主要是由潮汐流增强的两次昼夜事件之一驱动的。对模拟结果的回归分析表明，河流羽流长度与水位和河流流量密切相关，并且可以根据弱风条件下的前期河流流量准确估计它们。