河口地形的形成多依賴長期穩靜變動的河海營力，其平均能量對河口的形成與破壞是緩慢累積的，但是颱風、豪雨等突發事件所帶來的最大能量，其對河口塑形的重要性卻常遠較平均能量為大，往往造成河口地形在短時間內顯而易見的變動。本研究以中港溪口與水璉溪口為對象，利用野外沙洲剖線實測、粒度分析、數值地形等方法，探討研究期間颱風事件對河口沙洲的改變情形。主要目的在於了解河口在颱風事件的強烈能量下的反應情形，並比較不同規模與性質河口的差異性。期能藉由河口地形變動特性的認識，提供下游地區環境災害的預防及開發利用之參考。 研究得知水璉溪口經歷啟德和碧利斯兩個颱風後，河口沙洲被沖刷後退，兩岸沙洲壩變窄而陡；中港溪口在桃芝颱風後，河口沙洲形態變動幅度不大，但納莉颱風後，右岸河口沙洲幾乎全遭沖毀，殘餘的沙洲略有外海偏移的現象，河口沙洲坡度皆變得陡峭，顯示納利颱風對河口地形產生莫大的影響。比較中港溪與水璉溪河口地形對於颱風事件的反映差異，可以得知河口主導營力是重要因素。以潮汐為主控營力的中港溪口，受颱風事件的影響，「逕流+滿潮」的沖刷作用遠超過風浪增強來得重要；而水璉溪口在特殊事件下以風浪為主導營力，受颱風事件的影響，「風浪」的沖刷營力則遠超過逕流增加等作用。再者，水璉溪流域面積小，颱風事件後三個月已大致回復颱風前沙洲形態。而河口粒徑與水璉溪口相近的中港溪口，流域面積為其16倍，在納利颱風過後一年，河口沙洲形態仍未回復。則又說明河川規模是河口地形變動的重要因素；也說明不同事件所造成的河海營力規模，亦是河口地形變動的關鍵因子。

　　　　　The morphology of estuaries is constantly adjusted to the coastal and fluvial processes, which work on various temporal scales. The most significant changes of estuaries in Taiwan is believed always occur druing the typhoon periods which are with severe tidal/wave climates and/or very heavy rainfalls. Based on the repeated surveys and grain size analysis of sand bars at river mouths of the Chung-kang Hsi and the Shui-lien His for more than a whole year, respectively, this study aims to understand the geomorphic effects induced by typhoon events and the different recovering behaviors between two rivers after the events. Some conclusions are reached. During the study period, the sand bars of the shui-lien Hsi were eroded back and became narrower and steeper during the Typhoon Kaitak and Typhoon Bilis, whereas the sand bar of the Chung-kang Hsi was almost entirely diminished during the Typhoon Nari. Severe storm waves during typhoon periods are very destructive to the sand bars and usually cause significant morphological chang as what happened in the case of the shui-lien Hsi over the Typhoon Kaitak and Typhoon bilis. Analysis shows, however, for an estuary with much larger tidal range as of the Chung-kang Hsi, the coincidence of the storm waves, high tide and river flood is crucial to the disappearance of its sand bar during the Typhoon Nari. After the destructive events, the sand bars of the shui-lien Hsi were restored within 3 months, while the recovery of the sand bar of the Chung-kang Hsi has not completed over a whole year. Factors like the size of the catchment area, sediment composition of sand bars and the magnitude of these typhoon events are believed all contributed to this difference.