早期對飛砂研究認為風力作用是影響之主因，而海岸飛砂位於海－陸－氣交界區域，此處飛砂受海灘表層含水量影響非常劇烈。本研究針對海灘表層砂，以水氣收支平衡觀點探討表砂含水量之變化及其對海岸區域飛砂現象之影響。本研究在桃園新屋永安漁港南岸海灘進行現場實地觀測，海灘最表層含水量同時以重量法和影像法兩種方法進行量測，得到表砂含水量變化特性。進一步將重量法及影像法結果進行比較，探討影像量測方法的準確性與可行性。研究結果發現，潮汐是影響飛砂現象重要的因子，大潮差是發生飛砂的必要條件，當大潮的時候，若地下水位低於零通量面，表層砂含水量隨時間呈指數遞減，蒸發量越高，指數遞減越快，即發生飛砂。本研究提出表砂含水量指數遞減公式，透過資料分析區分潮位與蒸發量變化對表砂含水量之影響，可藉由此法評估表砂含水量指數衰減斜率來估計某個區域是否達發生飛砂之機率。Previous studies have shown that the wind speed is one of the most dominant controls on aeolian sediment transport. Coastal zone is at the interface among the ocean, atmosphere and the land, where the effects of the moisture content of the top few grain layers (surface moisture) to aeolian sediment transport is even important. This study highlights the dynamic spatial and temporal variability in surface moisture content on mild-slope beach.In this study, the observations were carried out at Yung-An Beach, Xinwu, Taoyuan. Two methods, surface brightness method and gravimetric method, were adopted to measure surface moisture. Furthermore, comparisons of surface brightness content and gravimetric moisture content in an attempt to examine the accuracy and possibility of the surface brightness method was implemented.The results demonstrates that the tidal difference is an important control on aeolian sediment transport in Yung-An Beach. Spring tide is the necessary condition that the surface moisture could be reduced to certain level that its corresponding wind speed thresholds for aeolian transport is less than the ambient wind speed. When the spring tide if the groundwater table is lower than the zero flux plane (ZFP), surface moisture decreases with time in exponential decay. Intensive evaporation due to wind and solar radiation results in faster surface moisture decay and allows the aeolian sand transport. Present study applies data analysis to separate the effects of tide and evaporation on the surface moisture. We proposed a surface moisture content decay formula to assessment the possibility of the occurrence of aeolian sediment transport decay in the mild-solpe beach environments.
