七股沿海地區地覆變遷分析

Analyses of Land-cover Changes in the Qigu Coastal Zone

本研究以台南市之七股沿海地區1994年、2004年及2010年等3期SPOT衛星影像資料進行影像變遷分析，探討該地區之地覆變遷情況。綜合1994年與2010年衛星影像變遷分析，七股沿海該16年間主要變化如下，七股鹽田與魚塭部分區域原為水域轉變為荒地，部分區域原為乾涸之後海水流入；網子寮、頂頭額及新浮崙等離岸沙洲朝東與朝南漂移；另位於頂頭額沙洲南段之防風林與沙地大幅消失；黑面琵鷺保護區之東南與南側，原為沙地被開挖為養殖魚塭；曾文溪口河床則有遭洪水沖刷現象。此外，該期間七股沿海植被消長情形分析如下，七股溪口生長之紅樹林原先主要有3塊，面積合計6.2ha，2010年僅剩1塊紅樹林面積減為5.1ha；網子寮沙洲北段原有14.4ha植被消失，網子寮沙洲南段防風林造林面積由4.2ha增為14.8ha；頂頭額沙洲北段防風林面積由8.5ha降為3.7ha，殆此期間沙洲遭侵蝕所致；另頂頭額沙洲南段之防風林則遭侵蝕而消失，1994年面積高達87.8ha，至2010年僅剩7.3ha。由影像變遷分析結果顯示，七股沿海離岸沙洲有朝東南方向漂移趨勢，殆與沙源補充、沿岸流、波浪及東北季風等因子有關，造成海岸嚴重侵蝕，尤其頂頭額沙洲南段之防風林面積不斷地縮減，甚至可能完全消失，亟需積極進行各種固堤與護沙措施。

Remote sensing images taken by French SPOT satellites showed that there were changes in land covers in the coastal zone of Qigu in 1994, 2004 and 2010. Specifically, an analysis of images taken over the past 16 years revealed a number of changes. Firstly, sediments had eroded and were deposited in Wangziliao, Dingtou'e and Xinfulun offshore sandbars, which drifted east and/or south. Secondly, the southeast and southern areas of the Black-faced Spoonbill Refuge had been replaced by fish ponds. Finally, the riverbed was shown seriously eroded at Cengwen estuary. In addition to these changes in land covers, losses in coastal vegetation were also documented. In 1994, there were three mangrove swaths with a total area of 6.2 ha in the Qigu estuary. However, two of these were excavated in 2008, and in 2010 only an area of 5.1 ha remained. While the windbreak forest increased from 4.2 ha to 14.8 ha at the southern Wangziliao sandbar, its area reduced from 8.5 to 3.7 ha at the northern Dingtou'e sandbar. Another windbreak forest eroded and disappeared at the southern Dingtou'e sandbar, an area of approximately 87.8 ha in 1994 that diminished to only 7.3 ha in 2010. The windbreak forests have seriously eroded and may even disappear completely at the southern Dingtou'e sandbar. Therefore, urgent stabilization of the sand bank of this region is recommended in order to protect the greater Qigu area from further deterioration.