賀伯颱風災害後嘉義山坡地新增裸地之空間分析

Spatial Analysis of Bare Land Increment Caused by the Herb Typhoon in Chiayi Slopeland Area

林金樹(Chinsu Lin) ； 陳永寬(Yeong-Kuan Chen) ； 劉正川(Jenq-Chuan Lieu)

《中華水土保持學報》 30卷3期 (1999/09) Pp. 223-233

https://doi.org/10.29417/JCSWC.199909_30(3).0006

摘要

台灣地處亞熱帶，地勢陡峭，河川短急，豪雨容易造成山區土石崩落及土石流等天然災害，尤以夏季颱風季節爲甚。若能瞭解災情以及災害發生地點之空間特性，將有助於政府推展災後救助與復建工作，也可供天然災害防治與土地管理工作之參考。1996年7月31日至8月1日賀伯颱風（Herb typhoon）在台灣中南部地區造成嚴重災害，本研究以嘉義地區爲例，利用衛星多譜資訊調査1996年夏季和冬季時期的嘉義山區裸地之分佈，藉以分析賀伯颱風前後，嘉義山區裸地面積的變化及新增的裸地之空間分佈特徵。研究結果顯示，1996年夏季至冬季嘉義山區新增加的裸地面積有9726.80公頃，約合全區面積之8.69%，各山區鄕鎭中的新增裸地面積多大於1000公頃，其中以分佈於阿里山鄉境內之面積2706.9公頃最多。新增的裸地區塊與溪流或道路相鄰的面積有2812.35公頃，佔全部新增裸地面積的28.9％，而且同時位於溪流及道路兩側的新增裸地區塊有900.63公頃，是所有與道路、河流交會的新增裸地面積之32.0％，這種現象反映出對山區溪流兩側土地保護措施之重要性，同時更顯示出通過溪流兩側之道路橋樑附近土地保育的重要性。裸地原生面積以平坡級2013.44公頃最多，並依坡度之增加而逐漸減少，至絕坡級348.25公頃最少；新增的裸地面積主要分佈於坡度35°以下的坡地中，約佔全部新增裸地面積的85％。裸地原生率和裸地新生率在各坡度級中分佈，卻呈現反抛物線型態之分佈，其反曲點位於急坡級，即坡度在25°-35°之間。賀伯颱風後的裸地新生率，以林木區之0.06最低，果園、檳榔、茶園等開發性的農業地區之裸地新生率約爲林木區之6.5～10.5倍，証明了林木被覆的土地，抵抗外來強風豪雨災害的能力最高，而經濟型農業植生區的土地則很容易受外來因素破壞，而發生土地崩裸之現象。

關鍵字

遙測 ； 地理資訊系統 ； 災害調査 ； 空間分析

並列摘要

Steep terrain relief and unstable river system in Taiwan make landslides and massflows happen frequently when a storm visits there in the summer period. Such natural disasters usually cause huge property damages and loss of human lives. Understanding the location and influences of natural disaster is important and helpful for post-disaster financial support and the environmental restoration. It could also be a good reference for prevention of natural disasters and planning the land management. The Herb typhoon visited the middle-south part of Taiwan on July 31, 1996, and resulted in serious landslides and massflows. After that event, the eroded mass settled down and became barelands. In this study, SPOT XS images of new barelands and their spatial pattern in Chiayi slopeland area, middle-south area of Taiwan, were analyzed: The results showed that the area of new barelands from June to December 1996 was 9726.72 ha which were about 8.69 % of the whole area. New bareland area that happened at each site is more than 1000 be, and Alishan was the largest. 28.9 % of the new bareland patches, or 2812.35 ha, were nearby rivers or roads, in which 32.0 % (900.63 ha) was located on the site where the rivers and roads pass through. This phenomenon demonstrated the importance and necessity of conservation for the land nearby the streambank and roads. In view of land slopes, most of the new barelands were distributed on slopelands under 35 degree. The percentage of both original and newly-happened barelands are decreasing from the 1^(st) slope class (less than 5 degrees) down to the 4^(th) slope class (from 25 to 35 degrees) and then increasing, and look like a parabola. The percentage of newly occurred barelands in developing cover types, e.g. orchard, areca, and tea field etc. is about 6.5 to 10.5 times larger than that in the forested area. It proved that the storm damage resistance of forest is the largest in all vegetative cover types.

並列關鍵字

remote sensing ； GIS ； disaster survey ； spatial analysis