雙溪河口沙洲地形變動之成因探討

A Study on Quarrying Changes on the Estuarine Landforms of Shuang-Xi

黃俊彰(Jun-zhang Huang)

指導教授 ： 林雪美

國立臺灣師範大學/文學院/地理學系/碩士(2003年)

摘要

摘 要
河口是聯繫陸地與海洋的重要管道，包含河川、陸地、海岸三方面，在海陸營力系統作用下，明顯為水流與泥沙的動力轉換點，呈現高度的複雜性與敏感性；河口的堆積形態也會因波浪、逕流與潮汐的交互作用而有所差異。
雙溪河口沙洲為台灣北部頗負盛名的海水浴場。近年，由於沙嘴形貌顯著改變，1999年動工的核四重件碼頭成為眾矢之的。但影響海岸地形變動的原因複雜，需詳加分析才得以釐清。本研究以近一年的海灘剖面實測資料，探討雙溪河口沙洲在無颱風年下的變動情形，另外，也比對歷史航照找出突發事件對沙洲的影響，藉此探究影響雙溪河口沙洲地形變動的因子。
本研究結果得知，影響雙溪河口地形變動的因子有：1. 颱風強度、路徑、發生的季節與間隔時間，2.豪雨，3. 強烈東北季風引起的波浪，4.漁港的興建等四項。颱風的路徑及其所引起的豪雨逕流或波浪營力增強等因素，會造成雙溪河口左、右兩岸沖淤位置與變動量的差異，甚至造成原出海口淤積而形成新的出海口。至於沙洲地形的回復狀況，則需視來襲的颱風強度，及與下次颱風的間隔時間。依據歷年航照數化比對以及年內實測，在無接續強勁颱風的影響下，推估雙溪河口沙洲回復期大約是10個月。由豪大雨帶來的陸象逕流營力增強，往往造成左岸沙嘴斷裂，其回復需要3-5個月的時間。本研究得知，東北季風的波高大於2公尺時，會出現沙洲體積減少、灘面後退、變陡等形態改變，且波高大致與河口沙洲體積呈反比關係。河流沿岸工程方面，雙溪河口右岸的福隆漁港在1993年興建完防波堤後，其西側淤沙面積確有逐年增加的趨勢，顯見鄰近漁港的興建對於雙溪河口沙洲變動較具貢獻度。

關鍵字

雙溪河口 ； 東北季風 ； 颱風 ； 豪雨

並列摘要

Abstract
Estuary is an important channel to connect the land and oceans , including three aspects: river、mainland and coast；under the influence of mainland and ocean physical strength ,estuary apparently is an motive turning point of flowing water and silt, presenting its complexity and sensitivity.
Shuang-xi Estuary is a famous bathing beach in North Taiwan. Recently,with the noticeable changes in the shape of spit, Zhong- jian dock established in 1999 becomes a target of the public criticism.There are many reasons to cause changes in coast topography and must make much research to make out.According to the findings of the one-year field work and in comparison with the aerial photographs,we attempt to find the key points that change Shuang-xi Estuary’s landform.
Based on the result of the research,we conclude four factors that changed Shuang-xi Estuary’s landform. 1.Typhoon’s intensity、path、season and interval time between two typhoons 2. cloudburst 3.wave arising from northeast monsoon 4. Fu-Long fishery harbor. Strong run-off and wave that arise from typhoon will bring about some variation in the sites of erosion and aggradation on right and left banks at Shuang-xi Estuary,occasionally even making old outlet deposition and then forming new outlet. According to the one-year field work and in comparison with the aerial photographs,if there are no successive typhoons attacking, geomorphological cycle of this estuary is supposed to be 3-4 years or so.Besides ,strong run-off arising from cloudburst always destroy the spit on the left bank ,and it needs 3-5 months to recover its former landform. Based on the research,when the wave height is over 2 m,it will cause some changes in the beach’s landform such as reducing volume of the sandbar,beach retreat and become steep；besides , the wave height and the volume of the sandbar are in an inverse proportion.As to the other engineering along the bank, in 1993 ,Fu-Long fishery harbor was built on the right bankof Shuang-xi Estuary, after that,aggradation of its area has become larger and larger on the west side of the harbor year after year.It demonstrates that Fu-Long fishery harbor had much influence on Shuang-xi Estuary’s landform.
At Shuang-xi Estuary ,the landform change is related to natural and man-made projects .In this study,we analyze alterant characteristics of Shuang-xi Estuary in one year、the effects and recovery by typhoon events and to differentiate each effect from various river and coast engineering. The results we get could provide insights to schemes and developments at estuaries by the operation of bathing beach and the public river and coast engineering.

並列關鍵字

Shuang-xi Estuary ； northeast monsoon ； typhoon ； cloudburst