河階地的對比與成因

River terraces correlation and their genesis

台灣的河階地因為植被覆蓋，經常缺乏良好的露頭，且沉積物富含礫石，透水性佳，以致於年代資料獲得非常困難。因此，階地的對比經常僅用階地面與現河床的高差，及其沿著河谷的變化趨勢。這樣的對比方法忽略了形成厚層階地沈積層的河川加積作用，使階地對比常常帶有較多的主觀成分，也使階地對比結果過於複雜，難以解釋。筆者以近年來進行河階地調查、對比、分析的經驗，提出具體實用性的方法。這個方法在實行上是依據野外調查所得的階地特徵，推論形成階地的河川下切過程，並在野外調查的同時依據階地特徵所顯示的河川下切過程進行對比。目前已經獲得良好的成果，希望這樣的方法能對其他地區的階地研究工作提供助益。

Due to the terrace scarps are usually well vegetated or covered by colluvial and the terrace sediments are highly permeable, to investigate the properties of fluvial terraces is very difficult in Taiwan, especially the dates of their sediments. Therefore, the most important criteria for correlating terraces are usually the height of terrace scarps and their trend along river valleys. However, the thick terrace sediments that deposited by aggradational processes are always neglected in that procedure. The results of terrace correlation will be involved too much subjectivity and complexity to make a reasonable explanation. The aim of this study is to propose a method, which will be of practical value to solve these problems in investigating, correlating and analyzing river terraces, and explain their genesis. It will be helpful in reconstructing landscape evolution models for drainage basins in Taiwan.