臺灣近百年來主要河流的地形變遷與其減災意涵：一個「人為地形學」的嘗試

The term Anthropocene, firstly introduced to the world of science by Crutzen and Stoermer (2000), has been introduced to highlight the fact humans have, directly or indirectly – accidentally or intentionally – profoundly transformed the earth system (Meadow, 2016). Along with this academic discussion context, Anthropogenic Geomorphology as a sub-branch under Geomorphology, has been proposed. It is regarded by the current author as an appropriate perspective to examine the geomorphic change induced by human impacts on the former active floodplains in various ways over a centurial time span in a highly geomorphologically-dynamic, natural hazard-prone and densely-populated island, Taiwan. The specific objects include: to examine the accessibility and validity of various pictorial materials and historical archives which may convey information on geomorphic change, to discuss the operational definition of “natural” channels and active floodplains and their guidelines of delineation, and to investigate the progress and key factors which result in geomorphic change on the different types of formerly active floodplains. The database of Taiwan historical floodplains is constructed based on the sequential pictorial materials, including those for 26 major streams around Taiwan island and 25 secondary streams in western Taiwan, and the former water bodies along the SW coast. The guideline for fluvial territory delineation is proposed and, based on this procedure, the transformation of the former active floodplains with braided channels to single channel pattern of the Wu Stream and the Holong Stream along with the channelization is clarified. When adopting the historical map overlap analysis, the consistency of mapping standards is the major concern especially for those historical maps in early stages.