本文結合HEC-RAS 3.0水理模式與RHABSIM 2.2棲地模式，以大漢溪中游為研究樣區及台灣特有種台灣石魚賓為標的魚種，推求該樣區之生態基流量，再針對此標的魚種在研究樣區設置堰壩水工結構物，進行棲地環境之改善並分析高壩與連續低矮壩對於該河段棲地之影響及壩之經濟效益。 本研究利用RHABSIM棲地模式在低流量狀態下進行棲地分析，發現棲地面積所對應之流量分別在3cms與16cms時為其明顯之轉折點，若以生態為唯一目標時，建議以16cms為生態基流量，因本研究樣區必須考慮水源利用效率，若以16cms為研究樣區之生態基流量，太過於嚴苛，所以選取3cms為本樣區之生態基流量。當在河川中設置堰壩，在低流量狀態下可使棲地面積增加，可見此水工結構物扮演著擴大棲地之功效且壩高與棲地面積並非成正比關係，而連續低矮壩在某些配置上棲地面積優於高壩，若以生態考量為主時，可選擇適合之連續低矮壩組合，達到改善棲地、擴大棲地之目的。決策者亦可根據設置堰壩所產生之經濟效益，有效的利用水資源。 This paper combines hydraulic model HEC-RAS 3.0 and habitat model RHABSIM 2.2 to calculate the ecological instream flow of the habitat by using Acrossocheilus paradoxus as target species in the midstream of Dahan river. Different influence from a high-weir or a series of low-weirs in research area was analyzed. The change of habitat and the economical benefit of weirs were also discussed. Analysis of RHABSIM model to habitat in the condition of low flow was performed. To achieve ecological requirement, the instream flow is estimated to be 16 cms. However, 3cms is proposed to be an adequate alternative given economical consideration of shortage in water resource in this region. It is concluded that building the weir in the river, in the condition of low flow makes the habitat area increase. In other words, the structures play an important role in augmenting habitat. Besides, one may notice that the height of weir and the area of habitat are not in direct proportion. Setting a series of low-weirs is better than setting high-weir in some conditions in terms of providing habitat area. Therefore, it is suggested that habitat condition can be improved by using the combination of proper series of low-weirs. A policymaker can provide the water to the institutions in need by choosing the weir setting which produces the highest economical benefit.