全臺流域集水區崩塌土砂收支研究與探討－以莫拉克颱風前後期間（2008～2012年）為例

Abstract

臺灣集水區坡地土砂生產中以崩塌所佔比例較高，崩塌土砂收支包含崩塌土砂生產量、流出土砂量及殘留土砂量，其為複雜交互作用，本研究為了解集水區崩塌土砂收支特性，使用概念模型描述崩塌土砂收支行為，基於降雨為誘發崩塌以及河道輸砂的主要誘發因子，透過崩塌體積-面積關係式推估崩塌土砂生產量，基於HEC-HMS 建立降雨-逕流模式，輔以流量-輸砂量率定曲線推估流出土砂量，根據集水區土砂收支平衡原理，推求流域集水區殘留土砂量。綜觀臺灣歷年土砂收支以2009年莫拉克颱風最多，莫拉克颱風前後(2008~2012 年間)崩塌土砂生產量以高屏溪流域的6 億4,344 萬立方公尺最多，其次為南台東河系(3 億679 萬立方公尺)與濁水溪(1億3,771 萬立方公尺)；流出土砂量以高屏溪流域的3 億5,401 萬立方公尺最多，其次為濁水溪(3 億5,041 萬立方公尺)；殘留土砂量以高屏溪流域最多(2 億8,944 萬立方公尺)，其次為南台東河系流域(1 億8,827 萬立方公尺)。綜合上述，本研究完成2008-2012 年間，全臺流域尺度崩塌土砂收支分析，期望對流域綜合治理規劃及土砂出流管制有所助益。Sediments originated from landslides occupies the major proportion of sediment budget of catchments in highly active orogenic belts of Taiwan. Sediment budget defines and quantifies the processes of production, transportation, and residual. The processes among these categories are highly interacted with each other. To understand the characteristics of sediment yields and the sediment budgets in Taiwan, this study integrated a conceptual modelling approach to quantify the amounts of sediment production, transport, and residual of watersheds in pre- and post- Typhoon Morakot periods (during 2008~2012 periods). We calculated the landslide-induced sediments production by using multi-temporal landslide inventory and volume-area relations derived from 2,535 landslide samples. The amount of sediment transport was simulated from a rainfall-runoff model (HEC-HMS) and rating curve relations between river and sediment discharges that developed based on field survey from WRA. Based on the principle of mass conservation, the sediment residual was calculated by the amount of sediment production minus the transport of a catchment. The results show that the Typhoon Morakot in 2009 triggered massive landslide-sediment and which is significantly over the capacity of sediment transport. Among all the watersheds during 2008~2012 periods, the Kao-ping River has highest sediment production with 643 × 10^6 m^3, and the second and third highest values are in the South-Taitung and Chou-Sui River with 367 × 10^6 m^3 and 137 × 10^6 m^3, respectively. The top two watersheds of highest sediment transport is the same with that of highest sediment production. The Kao-Ping River and Chuo-sui River transported 354×10^6 m^3 and 350×10^6 m^3 of sediment, respectively. In residual sediment, the Kao-Ping River catchment remains the highest sediment with 289 × 10^6 m^3; and the South-Taitung Catchments is the second highest with 188 × 10^6 m^3. The processes and results of sediment budgets analyzed in this study are expected to benefit the policies for watershed general management and to control landslide-induced sediments under the circumstance of extremely highly rainfall (e.g. Typhoon Morakot in 2009, which rainfall was more than 3,000 mm in 3 days).