淡水河口環流與淡水舌之研究

Investigation on the circulation and river plume in the Tamshui estuary

林聖烈(Sheng-Lieh Lin)

指導教授 ： 詹森

國立中央大學/地球科學學院/水文與海洋科學研究所/碩士(2006年)

摘要

淡水河為台灣北部主要河川，流經大台北地區，河水中所帶的污染物質相當可觀。河口為河流與外海傳輸的交界處，若能瞭解該處的動力機制，對河口海域環境保護有相當大的幫助。淡水舌(plume)是河口最容易觀測淡水與海水彼此作用的現象，本研究透過蒐集有關
潮汐、海流、流量、風速風向與人造衛星遙測影像五部份的資料，來瞭解淡水舌大小、型態上的變化是受到幾種因素影響，進而探討河口環流流場、溫度場、密度場與鹽度場。研究結果顯示，淡水河口海流主要受到半日潮潮汐週期性的影響，流向主要是東北、西南向，潮流振幅大小為1 m/s，當河流日流量在200 m3/s以內，淡水舌在表層的面積在70平方公里內。當日流量200 m3/s以上時，淡水舌的面積大於70平方公里。當淡水河流量大量增加時，會在流場表層產生流出河口方向的海流，最大流速可以達到2 m/s。透過鹽度水深剖面資料與流場水深時序資料的分析，推測淡水舌的剖面厚度大約5到10公尺。海流與潮位彼此有著固定的時差關係：當低潮時表層流出河口方向的海流河流主軸方向上(西北、東南向)流速可達最大；在高潮後2至3小時的時間潮波方向上(東北、西南向)的流速達可最大值，兩者透過數值模擬結果也是相同。

關鍵字

淡水舌 ； 潮汐 ； 人造衛星影像

並列摘要

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.

並列關鍵字

plume ； tide ； satellite image

參考文獻

張菀文，2002：淡水河口地形變遷之研究，國立臺灣大學地理環境資源研究所碩

大學地理環境資源研究所碩士論文。

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