本研究針對淡水河口沙嘴的風吹砂及水下沙丘進行現地監測與分析，並探討其形態及輸砂特性。風吹砂效應之研究乃分析風速及影像資料，以了解風場對淡水河口沙丘及灘線的影響，並以α值代表風場均勻之狀態。水下沙丘之型態則以Van Rijn(1984)方法進行分析，並估算沙丘運移距離。風吹砂研究結果顯示以主要風向及各風向均勻度，可判斷出控制沙丘運移之主要風向，於冬季時，風場最為均勻，沙丘運移距離也最大；本研究分析之沙丘運移結果，顯示淡水河口之風吹砂效應是向西南方運移，與灘線之變化趨勢不一致，因此，灘線變遷與風吹砂效應的關聯性不明顯。淡水河底床型態分析結果，顯示底床型態分類屬於沙丘。本研究分別於河口外(A)、河口內(B)兩段進行水下沙丘之測量，A段於8月7日至10月20日平均約向下游運移94公尺，B段於8月7日至10月20日平均約向下游運移65公尺。懸浮載的輸送量大於底床載，且在沙丘波峰處兩者都有較大值出現。;The aeolian sand transport and subaqueous sand dunes at the river mouth of the Tamsui River are explored in this study. The aeolian sand transport is analyzed based on the wind speeds and dune fronts on the sand spit of the Tamsui Rivermouth. The homogeneous state of the wind field is represented by a coefficient α. The dune forms on the riverbed are classified as lower regime dunes by using Van Rijn (1984) method. The aeolian sand transport are in line with the primary wind directions. In winter, wind field is the most uniform and the distance of sand dune migrated is the longest in the southwest dirction. While the beach line extents in the northeast direction at the same time. So the sand spit is many controlled by wave-induced littoral transport instead of aeolian transport. Two segments of sand dunes on the riverbed were investigated. One is outside the estuary (A) and the other inside the estuary (B). During the period between August 7 to October 20, 2014, the dunes migrated in the downstream direction with the distances of 94 meters and 65 meters, for A and B, respectively. Suspended loads are greater than bed loads and both shows peak values at the dune crests.