以環境指標優選大肚台地水源涵養區位之研究

Abstract

大肚台地屬入滲不易之紅土區，因坡度平坦致大規模開發案擴展快速，不透水鋪面增加致使地表逕流大量匯聚，在極端降雨事件逐趨頻繁下，易造成山坡地崩塌及土石流等災害發生，而下游都會區則易有淹水災情，因此找出崩塌及淹水災害之潛勢區位，對大肚台地之災害預防極為重要。 本研究以環大肚台地道路為評估對象劃定集水分區，利用極端降雨指標、道路開發指標及植生綠劣指標等指標計算集水分區脆弱度；而崩塌規模潛勢則採用土壤深度及河道凹岸攻擊等指標進行推估。另透過土地利用及土壤圖套疊，可得土地開發前、後之CN值(Curve Number)，據此篩選蓄水量變化較大之重點集水分區，最後優選集水分區漥蓄區位並提出相關營造對策。 結果顯示，大肚台地之南部因極端降雨及道路開發等指標較高，因此脆弱度較高；而南部之保安林區因土壤深度指標較高，為崩塌規模潛勢較大之區位；另依土地利用變遷之CN值變化可篩選出7處重點集水分區，當中變化最大之成功嶺亦位於南部，為防止超滲逕流造成崩塌及淹水之危害，可進一步優選重點集水分區之漥蓄區位，作為水資源涵養之用，營造如沉砂滯洪、景觀遊憩、調整微氣候、消防、灌溉及地下水補注等多功能之蓄水池。Dadu Terrace belongs to laterite with the characteristics of infiltration difficulty. Large-scale developments expand rapidly due to gentle slope at the top of the Terrace, and the increasing of impervious pavement causes large amount of surface runoff during the torrential rain. Under the condition of extreme rainfall event frequent occurrence, the Terrace is vulnerable to disasters of slope collapse and debris flow, and the downstream urban areas are easily suffering floods. Hence, it is important to find out the potential landslide and/or flood areas for the disaster prevention of the Terrace. Management units were delineated using the roads of Tai-No1, Tai-No1-2, County-125 and Taichung-77, and the vulnerability of each management unit can be estimated from the indices of extreme rainfall, road development and inverted Normalized Difference Vegetation. Landslide scale potential for the units can be extracted from the indices of soil depth and river concave. In addition, the curve number of pre- and/or post- development in a management unit can be evaluated using maps of land-use and soil, and then the hotspot units with the obvious difference in potential maximum retention could be filtered out. Finally, the depression storage sites extracted from the Digital Elevation Model in the hotspot units are recommended to propose the environmental creation strategies. Results show that southern terrace has the highest vulnerability because of having higher index value extreme rainfall and road development. The southern protection forest can be regarded as the areas with higher potential landslide. There are 7 hotspot sub-watersheds selected according to the changes of CN derived from land-use coverage. The hotspot sub-watershed, Cheng-gong hill, also locates on the southern terrace and is the highest changes of CN. In order to prevent landslide and flood due to excess runoff, the depression storage sites need to be filtered out from the hotspot sub-watershed for water resources conservation. The priority depression storage sites are strongly recommended to create the multipurpose ponds with the function of sedimentation and flood detention, landscape and leisure, microclimate adjusted, firefighting, irrigation and groundwater recharge.摘要 I ABSTRACT II 目錄 IV 圖目錄 VI 表目錄 VIII 第一章 前言 1 1.1 研究動機 1 1.2 研究目的 2 第二章 文獻回顧 2 2.1 紅土台地之生成 2 2.2 大肚台地之成因及環境 3 2.3 大肚台地土地利用變遷及環境問題 6 第三章 材料與方法 8 3.1 研究試區 8 3.2 研究材料 9 3.3 研究方法 10 3.3.1 集水分區分析單元劃定 10 3.3.2 風險度分析 11 3.3.3 崩塌規模潛勢分析 17 3.3.4 水資源涵養區位篩選 20 第四章 結果與討論 24 4.1 風險度分析結果 24 4.2 崩塌規模潛勢分析結果 28 4.3 水資源涵養能力評估 31 4.4 重點水資源涵養區位篩選結果 33 4.4.1 重點集水分區篩選 33 4.4.2 重點漥蓄區位篩選及營造對策 34 第五章 結論 47 參考文獻 4