Abstract
This paper analyzes velocity fluctuation of 30min to 60min period observed in the Tone River Estuary. First, the influence of the fluctuation on resuspension of sediment is assessed by analyzing near-bottom turbulence data. The result indicates that the fluctuation may enhance resuspension considerably. Second, the characteristics of the fluctuation are investigated. Spectrum analysis of cross-sectional average velocity and water level shows that there are several dominant oscillations whose frequencies coincide with the characteristic frequencies of seiches in the estuary. This result indicates that the velocity fluctuation is caused by higher harmonics of seiche. Furthermore, the external force causing the seiches and the response of the estuary against it are examined by comparison of frequency response functions estimated from observation and analysis. It reveals that the seiche is mainly caused by offshore water level fluctuation.
