Implementation and Current Channel Morphological Condition of Check Dams’ Partial Removal at Gau-shan Creek

27 Mar Implementation and Current Channel Morphological Condition of Check Dams’ Partial Removal at Gau-shan Creek

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Abstract

為建立七家灣溪支流高山 溪之連續性河川棲地環境，雪霸國家公園已自民國八十八年至九十年陸續完成對高山溪的 四座防砂壩所進行之壩體開口改善工程。雖然壩體改善後 之河道 演 變無法由 短時間觀察資料 加以推斷 ，然而 高山溪在 九十年秋天遭逢 桃芝與娜 莉颱風 之影 響，經歷數次洪水進而使得 河床沖刷演變甚為明顯。因此，本研究利用過去調查成果 與九十 年實施之四次完整現場調查資料 (分別於二、六、九、十月進行 )分析發現，高山溪三號防砂壩 以上河道在改善工程完成至 少十四個月以後，三、四號防砂壩壩體附近河床隨季節轉 變略有 變動，但其河道目前大致上 已達穩定狀態。而三號防砂壩以下河道則屬於壩體改善後 之初期 激烈變化期，因此壩體開口 的產生而造成壩體上游兩百公尺內河段之明顯沖刷情況。 而櫻花鉤吻鮭在無人工放流的情況 下，九十 一年五 月族群調 查所得數量比九十年十月增加約五十 尾，而且集中於棲地條件較佳之三號壩以上範圍。

English Abstract

With the experiences of dam body remodeling in previous years, this year’s research focused on the follow-up investigations on the morphological changes of observed channel cross sections, including those within dam sites of check dams No. 2 and No. 1 partially-removed in September 2001. According to the survey information collected in February, June, September, and October of 2001, the channel morphology beyond dam No. 3 stayed in stable condition. However, the channel around dams No. 2 and No. 1 is experiencing a rapid transformation period after partial dam removal due to the scouring at upstream channel banks ofthose two dam sites. Based on the survey result of Formosan Land-locked Salmon population within Guan-Shan Creek in May 2002, the population grew by 50 compared to that in October 2001 and the majority of the population was found in the channel above Dam No. 3.