| dc.description.abstract | The topological and tidal characteristics in the downstream reach of Dan-Shui River is explored in this study by employing field measurement, data analysis and the flume experiment. The median particle sizes of sampled bed material at different sites during last three years are within the range of 0.009 and 0.509 mm, while the bed material in Keelung River is coarser (between 0.1-0.4mm) than that of Dan-shui River. According to the topographical contour lines, the Dan-Shui river mouth does not exhibit an alluvial fan for water depth less than 10 meters .
Tidal behaviors in the river course, especially with the impact of approaching typhoons, become non-linear motions when compared with ocean conditions. Thus both the Harmonic analysis and the Empirical Mode Decomposition newly proposed by Huang et al.(1998) are adopted for data analysis of storm surge deviations. The latter one is suitable for non-linear, non-stationary data. The harmonic analysis can not completely filter out energy of the semidiurnal tide and may be unable to analyze the long-period component (Sa) in the non-leap year based on yearly tidal data. On the other hand, the empirical mode decomposition may effectively separate out the energy of semidiurnal tide, therefore the result is better than that of harmonic analysis. A better alternative to run the harmonic analysis is to take a three-year- span period for tidal analysis which results is better than the runs of either one-year or nine-year intervals. The storm surge deviations at the landward station, i.e., Tu-Di-Gong-Bi Station, is bigger than that of the river mouth station, i.e., the He-Kou Station, due to the flood effect.
The standing tidal wave is observed in the flume experiment, i.e., the water level synchronously changes at different locations. The phase lags of the velocity at different water depths and the surface elevation are around 90o. Similar flow characteristics is observed in the field site at Kuan-Du bridge. | en_US |