沖積扇的坡度以及水流量為影響水流功率的參數，本研究透過實驗探討沖積扇在不同供水、供砂量以及堆積扇坡度下的開析型態。本實驗選用細砂做為實驗顆粒以降低滲流的影響，實驗過程使用相機記錄，並透過影像分析量化開析過程。上游水砂入流條件分為清水及含砂水流兩個類別，第一類為清水由供水渠道進入沖積扇頂，經歷篩堆積、下切、展寬、自然堤階段。初期，向下滲流減少扇表面逕流，進而產生篩堆積，隨後的水流衝破篩堆積開始下切並於下游產生複成扇，而下切的水流在扇面形成渠道，並導致沖積扇開析，當下切趨緩，水流開始藉由側蝕展寬，而展寬過程中崩落的料源，最終導致河道遷移或持續漫灘。初始單寬水流功率與開析速度、渠道寬、複成扇面積、複成扇流動距離呈正相關。沖積扇發展過程根據水流功率大小分成三組別：ω_0>8N/m∙s為高水流功率，2N/m∙s<ω_0<8N/m∙s為中水流功率，ω_0<2N/m∙s為低水流功率，不同的組別產生與之對應的發展過程。第二類為不同含砂濃度情況下的開析試驗，每次試驗有數個供給循環，而循環的定義為清水、高含砂水流交替供給，結果表明沖積扇在高含砂水流階段有著穩定的扇面成長，且扇平衡坡度與水砂比成負相關，高含砂水流所發展後的開析渠寬大於清水沖刷乾堆積扇上時之開析渠寬。;The influence of stream powers on the dissection of alluvial fans is experimentally explored in this study by adjusting both the water discharge and the slope of the fan. The fine silica sand was used in this study in order to reduce the seepage effect on the fan surface. The sediment input at the upstream feeding channel for each run is either clear water or at a given sediment concentration. For the cases of clear-water feeding channel, the development of alluvial fan can be categorized into four stages, i.e., sieve lobe, downward incision, channel lateral expansion and natural levee. The increasing of dissection velocity, channel width, and the area of the composite fan are all well correlated with the increase of unit-width stream power. The evolution patterns of the alluvial fans can be classified as three regimes based on their ranges of initial stream power. There are the high stream power regime for ω_0>8N/m∙s , medium stream power regime for 2N/m∙s<ω_0<8N/m∙s and the low stream power regime for ω_0<2N/m∙s. For the cases of feeding channel with alternate cycles of clear water and sediment input with a constant sediment-water ratio, the channel and fan dissection appears during the phase of clear-water erosion while the sheet flow dominates and the channel incision is insignificant on the fan during the phase of turbid water. The fan slope increases with the decreasing ratio of water discharge to sediment discharge.
