| dc.description.abstract | Tamsui river is main river flows after the Taipei in the north of Taiwan, and the pollution brings in the river water is quite considerable. The intersection of river and open sea is estuary. If we can understand the mechanism, it will be quite helpful to the estuary environmental protection. Plume is a phenomenon that is the easiest to observe the fresh water and the seawater each effect in the estuary. This research collects five part of data about tide, the ocean current, the river discharge, the speed and direction of wind and the satellite image to understand how the size and shape of plume change under the influence, then we can discuss the estuary circulation, the temperature field, the density field and the salinity field. The investigation showed the ocean current in Tamshui estuary mainly is governed by semidiurnal tide. The current direction mainly is northeast to southwest, and the oscillation amplitude is 1 m/s. If the rivers discharge is less than 200 m3/s, the plume area approximately is 70 square kilometer. If the rivers discharge is more than 200 m3/s, the plume area approximately is 70 square kilometer. When Tamshui river increase massive discharge, it will produce a current to northwest in the surface layer. The current maximum speed can attain to 2 m/s. According to the data analysis of salinity in longitudinal section plane and the ocean current time series, we conjecture that the thickness of the plume is between 5 and 10 meters. In regard to the time relations of the ocean current and tide level when low tide occurs, the flows can achieve the maximum of the speed in surface layer, and the direction is to northwest (rivers main axle direction). Latter high tide occurs 2 to 3 hours, the flows can achieve the maximum of the speed in lower layer, and the direction is to northeast-southwest (tide wave direction). We also can find this result in numerical simulation. | en_US |