水砂比的變化會影響沖積扇的坡度，本文以不同實驗探討沖積扇在不同水砂 比情況下的坡面變化。90 度沖積扇實驗以細砂為實驗顆粒，上游條件分為清水沖 刷及高含砂水流兩種為一個供給循環。沖積扇在高含砂水流階段有扇面成長(前堆 過程)，其扇之坡度與水砂比成負相關，未經高含砂水流所覆蓋之扇面，其渠寬小 於被高含砂水流覆蓋扇面後之渠寬。四種實驗顆粒(細砂、粗砂、白色 PVC 顆粒 和褐色細磨石)在不同水砂比所對應之渠道坡度，均顯示渠道之坡度與水砂比成負 相關，本文並求得一無因次之坡度與水砂比之關係式。三種顆粒(粗砂、白色 PVC 顆粒和褐色細磨石)所得之無因次化之單寬輸砂量 qs *、無因次單寬水流功率 ω *及 Shields number Θ 三者均呈現正相關之關係。;The slope of an alluvial fan is mainly controlled by the water-to-sediment ratio of the feeding channel. The fan incision and progradation processes on alluvial fans under different water-to-sediment ratio conditions are experimentally explored in this study. Fan slopes for different particles and discharges were analyzed by image analysis with a camera and four laser beams. The equilibrium channel slopes as a funcion of the water to-sediment ratios were obtained for four dfferent particles (fine sand, coarse sand, white PVC beads, and brown mill stone), and an unified trend in dimensionless form agrees well with experimental data. The relationships among the dimensionless unit-width sediment discharge rate (qs * ), dimensionless unit-width stream power (ω* ), and Shields number (Θ) all depict positive correlations.
