圖書典藏及影音數位平台

因應極端氣候可能造成水庫淤積及發生水源高濁度等供水風險，人工湖開發為穩定提供水源之多元方案之一。考量臺南地區產業發展，用水需求將持續增加，仍需持續評估開發水資源，以達未來水資源需求。 臺南大湖近年完成相關調查規劃與檢討，具有做為工業用水水源條件，可提供南科臺南園區之用。為進一步探討臺南大湖開挖土方去化條件，及玉峰堰增加引取曾文溪水源後的水源運用，本年度持續辦理臺南大湖可行性規劃工作，以確認臺南大湖開發成本與供水能力，做為臺南大湖推動參據。

「Feasibility Planning (1) of Water Resources Development for Tainan Artificial Lake」 (abbreviated as this project) has been carried out in order to continue 「Environmental Investigation and Planning Re-evaluation of Tainan Lake」 by Water Resources Planning Institute, WRA, MOEA. During 2012, 2013, 2014 and 2017, the preliminary planning projects of Tainan Artificial Lake have been considering water supply, water backup, flood control, investigation of ecological and environmental, geological survey and promotion strategy. In view of the continuous increasing of industrial water demand in the Tainan area, a re-evaluation of this project needs to define its water resources utilization and project layout. Additionally, it is necessary to continue work on environmental resource investigation including geologic drilling, land-use survey, and groundwater monitoring to define the project function and benefit. Lastly, review of engineering planning. Following are summaries of the results of this project: 1. With a renewed water utilization and extended hydrological data, determining that the best development volume for Tainan Lake is 15 million cubic meter. The water supply capability is 100,000 CMD. 2. The results of geological drilling showed that most of the soil is silts. At the underground 5~14meter, there is a stratum of sand and gravel. At the underground 20 meter, there is a stratum of clay, regarding to an aquiclude. Based on the engineering planning, there is 3.73 million cubic meters residual soil. We suggest making good use of the surplus soils via the earth exchange process framework of Construction and Planning Agency. 3. Results of Environmental Investigation Groundwater levels observed in all wells are belonging to unconfined A-2 aquifer as the water levels rise with increasing rainfall. The flow paths following the topography and direction of river flow. The artificial lake area groundwater is not suitable for the water source of the artificial lake, because of high ammonia nitrogen, chemical oxygen demand (COD), and total organic carbon (TOC) are exceeding the standard of source of potable water quality standards. The water quality of runoff of Zengwun River at Yufong Weir is Type B. It is suitable to the source of water for the artificial lake. Thus, the water of Tainan Lake is drawn from Yufeng Weir and transported to the artificial lake via a 13.28 km water aqueduct. Moreover, the cutoff wall in the embankments can prevent the water of artificial Lake from the infiltration of polluted groundwater effectively. The total land of this project is 182.8 hectares, including 88.3% belong to Taiwan Sugar Corporation, 8.1% and 3.6% belong to national property and private property, respectively. There is an agricultural area and the main crop of this area is sugar cane. 4. Response Strategies for Sensitive Environment Area According to the evaluation of HBF method, we have predicted the project area, which is in the medium to high potential of soil liquefaction hazard influencing area. Results of analyses by Soilworks 2D software revealed that embankment slope would be unstable for the existing soil in case of seismic design. However, if the material is compacted to increase its strength, the factor of safely will be acceptable. Tainan Lake is located in the Jianan Plain groundwater recharge geologically sensitive area. According to the simulation results of the MODFLOW, which is the modular hydrologic model developing and releasing by USGS the annual net flow of groundwater seepage into the artificial lake is 76,000 cubic meters, which merely accounts for 0.08% of the annual groundwater recharge. Therefore, there is no significant effect to groundwater A-3 environment after constructing Tainan Lake. 5. Review of engineering planning of this project, concluding intake engineering, diversion engineering, artificial lake storage engineering. The estimated cost for development of Tainan Artificial Lake is 16.51 billion NTD, the cost of raw water is 20.33 NTD per cubic meter. 6. In view of the water supply capability, engineering feasibility, and engineering economy of Tainan Lake, it is worthwhile to construct Tainan Artificial Lake.