桃芝與敏督利颱風對濁水溪植被面積變遷之影響－－以濁水溪下游西濱至中沙大橋河段及清水溪南雲至龍門大橋河段

Impacts of Typhoons Toraji and Mindulle on Vegetations of the Lower Jhuoshuei River and Its Tributary Cingshuei Creek

本研究以桃芝與敏督利颱風前後之SPOT衛星影像資料進行影像變遷分析，探討颱風對濁水溪下游與其支流清水溪下游河段植被面積變遷之影響。分析結果顯示濁水溪下游西濱大橋至中沙大橋河段受2001年桃芝與納莉颱風挾帶豪雨沖刷，造成主河道之寬度明顯增加（最大增加約530m）、彎曲度減小、改道或分支等變化，河床植被有多處遭洪水沖毀或土砂覆蓋，植被相對面積由36.09%降為32.27%，翌年明顯增加為46.49%。2004年遇敏督利颱風侵襲，主河道位置再次顯著改變與呈現分支，部分植被亦遭洪水沖毀或土砂覆蓋，植被相對面積降為36.10%。清水溪下游南雲大橋至龍門大橋河段由於2001年桃芝與納莉颱風侵襲，主河道明顯往東位移，河床植被多遭洪水沖毀或土石覆蓋，植被相對面積由50.47%降為23.61%，2003年增為59.85%，至2004年又遇敏督利颱風侵襲，使主河道移位與分支，河床植被再度遭洪水沖毀或土石覆蓋，植被相對面積降為38.03%。 This study compared the SPOT satellite imageries taken at the lower Jhuoshuei River and itstributary Cingshuei Creek before and after each typhoon of Toraji in 2001 and Mindulle in 2004. Theresults showed that for the lower Jhuoshuei River, Typhoon Toraji in 2001 increased the river width, decreased the river curvature, shifted and branched the river course, and buried its vegetations withdeposited sand and soils; the vegetation area reduced from 36.09% of total riverbed area to 32.27%. Inthe following year, the vegetation area increased to 46.49%. After Typhoon Mindulle in 2004, the rivercourse shifted and branched again, and its vegetation area decreased to 36.10%. The fairly similar effectsof Toraji and Mindulle to the lower Jhuoshuei River were observed for the Cingshuei Creek. Itsvegetation area decreased from 50.47% to 23.61% in 2001 due to Toraji, increased to 59.85% in 2003,but decreased again to 38.03% in 2004 due to Mindulle.