應用溪流狀況指數(ISC)評估土石流整治溪流之適宜性探討

Abstract

本研究使用澳洲維多利亞省所發展之溪流狀況指數(Index of Stream Condition, ISC)評估模式，針對台灣7處土石流野溪進行評估，以探討應用於台灣土石流整治溪流之適宜性，並提出修正建議，提供未來建立台灣本土溪流狀況指數評估模式之參考。 根據本研究之結果，水文次指數分數偏低，但不能代表溪流狀況差，主因為自然地形及氣候所影響，故調整其分級標準，以符合現況；物理型態次指數之人工構造物指標並不適合台灣，野溪魚類已能在生態廊道遭受阻絕下生息，故本研究根據有無洄游性魚類之存在作為是否評估之標準，溪流物理性棲地指標無法評估豐枯變化大之野溪，本研究根據豐枯水期時間與有無常流水之比較，進行修正；濱河區域次指數之本土外來種指標操作不易且無必須性，故將之剔除，保留植生連續性及寬度；水質次指數因應台灣土石流野溪狀況，剔除磷、導電度，保留pH值，以總懸浮固體量取代濁度，加入水溫指標；水生物次指數以台灣保育類野生及特有種魚類，進行本土化之修正。

The purpose of this research is to assess the suitability of using Index of Stream Condition (ISC), developed by the State of Victoria in Australia, in managing debris flows at seven torrents in Taiwan. This research also provides recommendations about the establishment of local stream condition assessment models in the future. The results demonstrate that the number of Hydrology Sub-index was lower than normal. It did not mean that the stream conditions were bad, since natural topographies and climates did have an impact on it. Thus, standards for grading are modified to better reflect local conditions. This research also shows that it is not appropriate to utilize the impact of artificial barrier as an indicator in Taiwan because fish survived well even though corridors had been blocked. Therefore, the existence of fish is used in this research as the standard for assessment. It was also not able to evaluate the condition of instream physical habitat on torrents in which flow changes dramatically between rain and dry seasons, and thus this evaluation is modified according to flow conditions in rain and dry seasons. The assessment of native and non-native vegetation under the Streamside Zone Sub-index is difficult and unnecessary, thus it is not conducted in this research; the consistency and width of vegetation is assessed. Due to the actual conditions of debris flow in Taiwan, the total phosphorus and electrical conductivity are not assessed, and instead of assessing the turbidity, the amount of total suspended solids is evaluated. The research maintains the test of alkaline and acidity, and adds an assessment of water temperature. Aquatic Life Sub-index is modified to address the conditions of local endangered as well as endemic fish species.