圖書典藏及影音數位平台

莫拉克颱風造成曾文水庫及南化水庫原水高濁度暫時停止供水及水庫大量淤積後，更顯示未來將是氣候變遷降雨集中的趨勢，而台灣南部水資源運用面臨豐水期更豐、枯水期更枯的情境，致使南部水資源除考慮供給與需求的平衡，更須因應極端氣候發生洪災及水源高濁度等供水風險，也因此離槽水庫或人工湖已成為穩定區域供水之重要水源，而人工湖除了有供水功能外，其廣闊水域景觀更可提供生態環境與遊憩資源，兼具營造水與綠環境效益。 經濟部水利署水利規劃試驗所(以下簡稱本所)今年初已針對台南大湖之供水、備援、防洪及環境營造等功能進行檢討，目前已獲致近程提供曾文溪中下游滯洪空間兼具環境營造、中程協助現有水源設施穩定供水、遠程則依南部相關水資源計畫開發情境評估增供水源可能性之初步成果，做為台南大湖開發策略與功能與定位。 因此，本計畫將持續今年度計畫方向，進一步了解台南大湖地質條件與土壤特性，以確認土方去化之具體方向，並分析地下水水位、流向，以及台南大湖對地下水之影響，並就環境生態與生產型態進行調查分析，同時針對滯洪與供水進行相關工程規劃工作，以確認台南大湖未來各期程開發策略之可行性。

The objectives of this study are to understand geological conditions and soil characteristics related to the development of Tainan Lake, to evaluate approaches to dispose of excessive soil and to evaluate impact of the man-made lake on ground water. At the same time, to conduct ecological and land use surveys as well as to conduct initial planning of water supply scheme. Results are summarized below: 1. Results of geological drilling indicated that three strata exist within 25m below the ground surface. In sequence, they are: (1) Dark yellow silty send. (2) Dark grey silty sand with occasional intermeddling of cobble and gravel. (3) Grey silty sand, sandy silt or silty clay. Overall, most of the soil are silts. After evaluation, it was concluded that excess earth can be used for coastline protection within the Tainan City boundary. It may also be used for nearby farm land soil improvement. This will save cost of transportation. 2. Ground water is not suitable for drinking water or for irrigation, due to high arsenic level, ammonia nitrogen and conductivity. As for surface runoff, reaches downstream from Tsengwen Hsi Bridge on Tsengwen River and the neighbor drainage, due to poor water quality, it is also not suitable for public and for irrigation. Between Yufong Weir and South Irrigation Trunkline, water quality is suitable for public drinking and irrigation use and can be the source of the water for the man-made lake. Results of simulation indicate the man-made lake will affect the ground water in and around the lake. The ground water level can be expected to rise 0.5~2.0m. 3. Result of Ecological survey revealed that there are 3 type of protected species, including Crested Myna, Ring-necked Pheasant and Black-shouldered Kite. The total planned area is about 965 ha. Among than 621 ha are private land, 310 ha belong to Taiwan Sugar Corporation and 34 ha are public land. The lands are being used for farming. The products are sugar cane, rice, corn and pomelo, etc. The planned area may maintain the current farming practice. In the future, it may developed into organic farming in conjunction with the development of man-make lake. 4. The estimated cost for development to provide public water supply is 16.88 billions NTD. The cost would be lowed to 15.65 billion NTD, if it is developed to exchange with existing irrigation water. The later scheme is cheaper because there are no need for regulation pond and pumping facility. In addition the conveyance pipeline is shorter.