由於稀有動物保育意識逐漸受重視，政府乃將國寶魚櫻花鉤吻鮭復育列為重點計畫，其中又以防砂壩阻礙魚類迴游路線的問題需迫切解決，雖曾有魚道之設計，但並不成功。本研究為瞭解防砂壩改善成滯洪壩後，對棲息環境之影響及其改善效果，故利用室內水工模型試驗針對河床深槽線形成以及泥砂輸出歷線進行觀測。根據試驗之結果，本研究認為 以拆除部分壩體作為恢復河川魚類生態棲地環境之作法，對溪流安定及泥沙輸移均未造成激烈之衝擊，具有相當的可行性。若以不同拆除型式及拆除方式進行改善工程後，壩體上下游之坡度增率、淘刷深度、深槽形成、排沙增率及泥沙濃度增率等河床變化為考量因素，本研究認為最佳之改善方式為分次將雪山溪四號防砂壩改造成具梯形開口之滯洪壩。根據水文條件及櫻花鉤吻鮭之生物特性，本研究建議最適當之施工時間應為梅雨季來臨前之三、 四月份。

　　　　　 With higher recognition on conservation of endangered species in Taiwan, one of the major conservation projects for the government is the restoration of Formosan Salmon (Oncorhynchus masu formosanum) which is threatened by check dams in the channels for blockading the pathway to upstream and causing the problems of population isolation and close-blood mating for this treasure fish. Auxiliary fishways were investigated and installed to solve this problem, but their effect was decreased dramatically by the damage and deposit of sediment. By partially breaking the dam body or cutting opening appropriately, this study tried to provide alternative solution for this problem through model experiments. Based on the experiment results, this method of habitat improvement does not have serious impacts on channel stability and sedimentation. The best alternative from various combinations of opening types and destruction procedures for check dam #4 of Chi-Chia-Wan Creek is to convert the original dam into detention dam with trapezoid opening based on the considerations of upstream channel slope increment, scoring depth, flush flute formation, and downstream sedimentation increments on discharge and concentration. Besides, this study suggests that the best operation time for habitat improvement is between March and April before raining season according to hydrologic records and the characteristics of Formosan Salmon.