臺灣主要河谷氾濫平原百年時距的土地覆蓋變遷及其在洪水減災的含意

The rivers in Taiwan are characterized by steep gradient, contrasting seasonal discharge and coarse bedload. Although not easy to be tamed, all the major rivers in Taiwan have experienced significant river regulations over the 20th century.  One of them is the process of channelization with river dike construction especially along the middle and lower reaches. This practice has been applied to various channel planforms, including the less frequently flooded ‘river territory’ along the braided river reaches. Increase of extreme weather events of record-breaking high-intensity rainfalls and consequently severe damages since mid-1990s has caused major concern on flooding issue.     With the lower Wu River (c.a. 30 km in length) in central Taiwan as the study area, this study aims to understand how the channel pattern has been transformed. Landcover and geomorphic interpretation are completed by using historical maps, aerial photographs and orthomaps from early 20th to 2006 on a GIS platform. Government archives have been consulted. It is found that the channelization process along the Wu River started around 1920s and had intensified after Second World War. The master river management plans, usually initiated by severe flood hazards, seem to have multiple purposes, i.e., flood control and land reclamation. The flooded area induced by the Eight-Seven Flood in 1958, the largest event in the record, was within the former active-channels zone delineated from historical maps published in 1920s. It also contrasts the limited space of the ‘river reservation zone’, only in which the development is prohibited by the current law.