以涵容曲線評估鰲鼓濕地環堤水域水文調控之可行性

Assessing the feasibility of hydrologic alteration for peripheral waters of Aogu Wetland using storage capacity curves

臺灣位處東亞澳遷徙線上，鰲鼓濕地每年除黑面琵鷺（Platalea minor）度冬外，尚有鷸鴴類、雁鴨類、鷺科等水鳥族群度冬，各類群水鳥對水深偏好不一，若能依據地形與水文特性調控水位，可改善水鳥棲地品質。鰲鼓濕地環堤水域包含千島湖草澤、南方水池、西南草澤、西側草澤、西北側開放水域等處，本研究使用虛擬基站即時動態測量以步行及操筏對鰲鼓濕地環堤水域地形測量，建立各水域之水域面積、水深分布、蓄水容積等涵容曲線。並於各分區水域設置水位監測站，2017–2018度冬季環堤水域各區水位變動趨勢一致，由10月開始最高，一路下降至隔年2月春雨後開始回升，平均水位-0.6 m（Elevation, EL.）。以水深概略區分鷸鴴類與鷺鳥可用棲地，比較環堤水域水位監測紀錄與涵容曲線可發現，兩功能群可用棲地面積隨水位變化，於12月達最大值，但水位谷值與可用面積峰值發生時間不同，鷸鴴類可用棲地多寡依序為西側裸攤、西南草澤、西側草澤，鷺鳥則為西南草澤、西側裸灘，其餘水域可用棲地不多，鷸鴴類可用面積僅約鷺鳥1/4不到。由於濕潤裸灘為鷸鴴類主要覓食棲地，水位週期變動頻度可保持裸灘濕潤，有助於增加覓食棲地可用度。經分析探討可看出，鰲鼓濕地環堤水域排水條件較差，颱風帶來水量需藉助動力排除，但就引水改善各區水鳥棲地品質則具有相當潛力，但其水文調控需有因地適應的水文設計方案。本研究將水庫運轉規線觀念應用至鰲鼓環堤水域的涵容曲線建立，在經營管理實務上可透過涵容曲線，將園區長期監測的水位歷線轉換成水域面積歷線、各類群可用棲地面積歷線。透過現地管理人員的經驗累積，或是鳥類群集監測資料與水位監測資料的進一步比較分析，可建立最適化水位操作規則，改善水鳥棲地品質。

Taiwan is located at the midway point of the East Asian-Australasian Flyway. The waterbird wintering or stopover in the Aogu Wetland include shorebirds, waterfowls, herons, as well as the Black-faced Spoonbills (Platalea minor). Due to various preferences for waterbirds for water depths, altering water levels based on topography and hydrological characteristics is needed to create more habitats for each group of waterbirds. The peripheral waters of Aogu Wetlands consist of several connected ponds, such as Thousand Islands Lake, southern water pond, southwestern marsh, western marsh, and northwestern open waters. In this study, the water area, water depth distribution, and storage capacity curve of each pond were established through the virtual-based station real-time kinematic (VBS-RTK) topographic surveying by walk and boat. Water level monitoring was conducted three times a month at each water pond station. Results indicate that the water level peaked in October 2017, followed by consistently drawing down in the peripheral waters until February 2018, but after spring rains, the water level began to rise again thereafter. The mean water level of the period of time was -0.6 m (EL.). The usable habitats were categorized based on the preference of two major water bird groups - shorebirds and herons, and it was observed that the usable habitat areas for these two groups varied with the water level changes by comparing the records of water level monitoring with the capacity curve. The maximum usable area was reached in December, but the timing of the lowest water level and the peak usable areas were different. For shorebirds, the maximum usable habitat areas were mainly located on the mudflat of the western side, followed by southwestern marshes, and then western marshes. For herons, the maximum usable habitat areas were only on the southwestern marshes and the mudflats on the western side, and there were not much available habitats in other waters for herons. The usable areas for shorebirds were only about a quarter of those for herons. Since moist mudflat was the main feeding habitat for shorebirds, the periodic variation in water levels could keep the mudflats moist, thus helping to increase the availability of feeding habitats. Results indicate that the drainage conditions were relatively poor. The water brought by typhoons required dynamic drainage. However, improving water diversion has shown a significant potential for enhancing the quality of water bird habitats in peripheral waters. Nevertheless, hydrologic alteration must be adapted to local conditions with a well-designed hydrologic management plan. This study applies the concept of reservoir’s rule curves to establish the capacity curves for the Aogu peripheral waters. In management, the capacity curves allow the conversion of long-term stage monitoring into water surface area and available habitat area for various species. By accumulating the experience of on-site managers or conducting further comparative analysis of bird assemblage and water stage monitoring, an optimal water stage operation rule could be developed to improve the quality of water bird habitats.