臺灣西南海岸平原各河流的河道變遷，主要導因於曲流作用、暴風雨後主流的迅 速淤積，以及河口段的河道延長。八掌溪及曾文溪下游即分別發生過五次及四次的改 道，河道擺幅達20公里以上，但自1920年代河堤興建後，河道便少有大幅改道現象。 因海岸平原向西擴展，河流下游呈現延長河的特性，以急水溪為例，1904至1990年間 河口每年平均向西推移43m。 海岸平原地區向為人口稠密地帶，地形變遷常造成洪患威脅、土地利用改變、沿 岸聚落興衰、土地權屬爭議及行政區劃定等之衝擊。相反的，人類興建水庫、修築堤 防、開鑿渠道、河道截彎取直等作為，也造成天然地形之改變，地形變遷與人類生活 息息相關，其研究正可提供為土地規劃與開發利用的參考。

　　　　　Rivers in the coastal plain in southwestern Taiwan are notable for their meandering channels and high sediment yields. Two major rivers in this area, the Pachiang and the Tsengwen River, have avulsed five and four times, respectively, in the typhoon season by rapid sedimentation over last three hundred years. The shifting distance of channel avulsion, from north to south, for both rivers are more than 20km. However, these channels have been more stable due to the protection of river banks since 1920's. Responding to the coastal progradation, the rivers have lengthened westward. The river mouth of Chishui River, for example, has migrated 43 m/yr in average from 1904 to 1990. The river change of this area has exerted some impacts on people's life, such as the village relocation to avoid the river bank erosion, the decline of ship ports, and the confusion and controversy of the administrative boundaries. In contrast, human action, such as the construction of irrigation canals and dams and channel cutoff, have also caused impacts to the nature of river channels. Obviously, the river change and the human behavior has been interrelated closely to each other over last three hundred years.