石门水库集水区重大土砂灾害探讨

Sedimentary hazard analysis for Shihmen Reservoir watershed

由于2004年艾利台风及2005年马莎台风作用，石门水库高浊度之泥砂造成北台湾多日严重的供水中断，并造成重大经济损失。针对2次台风对于石门水库集水区崩塌地分布与地文、水文及人为开发等因素之间的关系，透过地理信息系统分析，探讨土砂的来源分布与致灾原因。结果显示：2005年马莎台风后水库集水区总崩塌地面积约为703hm^2，占整个集水区面积的0．92％；石门水库集水区坡度陡峭，地质破碎，加上超大豪雨与降雨集中等为造成水库严重土砂灾害之主要原因；根据崩塌量与历年水库淤积量之关系，台风豪雨所造成的重大崩塌事件，对于水库淤积量所造成之影响至少会延续5～10a。

The high nephelometric turbidity unit （NTU） in the Shihmen Reservoir during Typhoon Aere in 2004 and Typhoon Matsa in 2005 hit northern Taiwan jeopardized the reservoir operation for several days, which caused the severe economic losses. The study was implemented by spatial analysis with GIS from landslide sites versus physiographic features, hydrologic features, land-use, and aerial photo interpretation to trace the sediment sources and the reasons attributing to the slopeland hazards. According to the results, the total landslide area was 703 hm^2 after Typhoon Matsa in Shihmen Reservoir, which account for 0.92% of the total watershed area; The heavy rains triggered landslides and debris-flows on steep slopes and fragile regions. Abundant soil was transported into the reservoir, which was speculated to be the main reason for the high suspended sediment yields in the reservoir. According to the reservoir sediments investigation, the duration of the impacts of once mass landslide on reservoir sediment deposition was 5 to 10 years at least.