土壤發生入滲過程中，在特定條件下其濕潤鋒面會轉變為非穩定鋒面，原本平整之邊界受到擾動會逐漸加劇，最後形成如手指形狀之流動路徑，該類型之入滲路徑被稱為優勢流或指狀流。在流動過程中，水分皆沿著該路徑入滲，與傳統理論假設之均勻入滲相異，影響水分於土壤內移動之特性，進而影響對地下水補注。
本研究透過上層為細顆粒、下層為粗顆粒之層狀土壤結構，於透明沙箱內產生優勢流形式之水分移動，利用背光光源照射土體，透過延時攝影紀錄實驗過程中優勢流之發展，以照片量化水分在土體內部之移動。透過設定不同邊界條件，以定水頭邊界探討濕潤鋒面之形狀、移動以及入滲速度，描述優勢流作為地下水補注形式時之特性。以定體積邊界探討不同之供水條件下，在優勢流與均勻流入滲之差異，如何造成補注比例之差異，進一步影響實際補注地下水之總量。
結果顯示優勢流在有限供水情況，或是土層較深之情況下，能以較少損失量及較快之速度補注地下水，因此在乾燥氣候下或是對深層地下水層補注時，優勢流有其優勢存在。當供水充足情形，或是土層厚度較淺之情況，優勢流因其結構影響入滲量不再具有優勢，因此在濕潤氣候或是地下水層較淺時，優勢流並無明顯之優勢。

During the infiltration in soil, the wetting front would become unstable front under specific conditions. Original laterally uniform front would become a finger-liked flow paths due to the disturbance in soil. This phenomena was named as “preferential flow ” or “fingering flow”. All of the water during infiltration were traveled downward through those paths which is conflict with traditional theorem. This property would influence the water movement in soil; therefore, the supplement of groundwater was affected.
In this study, a series of experiment was conducted in sand boxes with layered soil, which has a structure of finer soil over coarse soil to create preferential flow. Photos were taken by high speed camera to record the development of preferential flow and was used to quantify the water movement by image processing. Different types of boundary conditions were used in experiments. Experiments of constant water depth were designed to discuss the shape, movement and infiltration rate of preferential flow as a supplement of ground water. Experiments of varied water depth were designed to compare the difference of recharge ratio between preferential flow and stable flow under different
infiltration condition.
The result shown that preferential flow is capable to supply groundwater with less loss and faster velocity if the water supplement is limited or the groundwater table is deep below surface. As a conclusion, we suggest that preferential flow may have the edge on ground water recharge in arid climates or deep groundwater table.

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