本研究使用高解析數值地形模型萃取蘭陽溪流域土石流潛勢溪流之地文參數，以了解各土石流潛勢溪流之集水區內溢流點、災害型態及影響範圍。研究區域之河流級序大多以一級與二級河流為主。集水區內之土石流潛勢溪流的地貌參數以各子集水區流域長(L)與集水區險峻值(MR)來判定土石流潛勢溪流具有可行性。統合三個流域資料及大陸土石流溪溝可得流域土砂災害之地貌分類為MR>0.43且L< 7km者為土石流；0.3≤MR≤0.43，且L≤14 km及MR>0.43，且7km ≤ L≤ 14 km者為高含砂水流及土石流並存；MR<0.3則為洪水。當溢流點下游有沖積扇時，堆積扇坡度與流域險峻值之關係可供判釋集水區是否為土石流潛勢溪流之參考條件。

The morphometric parameters associated with landslides and debris flow ravines in Lanyang River Watershed are analyzed in this study by employing the 5-m high-resolution digital terrain map and field studies. The total length of the first- and second-order streams present the majority of each watershed. The morphometric parameters such as Melton Ratio and drainage length are applied to identify the debris-flow prone ravines. However the use of Melton Ratio (MR) combined with drainage length (L) analysis results that are not classified as debris flow causes may be affected by slope, the geological or protected targets. The systemized geomorphic thresholds for debris-flow prone watershed are : debris flows for MR>0.43 and L< 7km；0.3≤MR≤0.43 and L≤14 km , or MR>0.43 and 7km ≤ L≤ 14 km for the coexistence of debris flows and debris floods； MR<0.3 for floods. The fan slope and the Melton ratio can also serve as an indicator for debris-flow ravines。

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