圖書典藏及影音數位平台

澎湖地區氣候深受大區域氣候影響，年平均蒸發量大於年平均降雨量，可知其水文條件極不利地表水資源之利用，因此，地下水成為澎湖地區長期仰賴的水資源來源。然而地下水持續過度的開發，已造成澎湖地區海水入侵及地下水鹽化等問題。由本署以往研究成果亦顯示，澎湖本島海水入侵量約佔深層地下水儲存量之2.8%，倘每一單位之入侵海水可鹽化36倍的地下水儲藏量，將嚴重影響澎湖地區水資源調配利用，因此，自來水公司為因應澎湖地區地下水鹽化問題，雖提出地下水減輪抽計畫，以避免海水楔持續入侵，同時逐漸將地下水轉為備用水源，以保育地下水資源，然其成效仍顯有限。 另外，為保育地下水環境，依本署訂定之地下水管制區劃定作業規範規定檢討，澎湖地區目前公告之地下水管制區包括馬公市全區、白沙鄉及西嶼鄉部分地段，限制區內地下水之使用。而依現行劃定作業規範規定，離島地區地下水管制區檢討係以水位、水質，以及高程等為主要評分因子，意即僅考量海水入侵潛在範圍，但因澎湖地區既有之地下水位觀測井密度稍顯不均，除增設地下水觀測井，並透過空間內插方式以取得更細緻網格評分資料外，亦可嘗試透過數值計算方式，模擬海水入侵邊界，以供地下水管制區範圍檢討相互比對驗證參考。爰此，基於地下水管制區劃定檢討及地下水資源保育管理需要，遂委託辦理本「澎湖地區海水入侵評析與防制策進措施」計畫，以澎湖本島之馬公市、湖西鄉、白沙鄉以及西嶼鄉為工作範圍，期可透過地下水水流及傳輸模擬分析，更進一步掌握海水入侵邊界，以利在空間上提高地下水管制區檢討評分精度，同時藉由地下保育措施，確保澎湖地區地下水資源之永續利用。

This project was undertaken to investigate the current stage of groundwater hydrology, usage, and salinization in Penghu. Literature studies on groundwater salinization in Penghu were first collected, and then fifteen wells were selected to conduct water quality test. Afterward, we evaluated, in qualitative and quantitative manners, the potential causes of groundwater salinization based on our test results, which provides useful information to build the geological model for numerical studies in Penghu. We applied MODFLOW and its sub-mode MT3DMS to simulate the groundwater level and seawater intrusion in Penghu, and proposed the remediation strategy for groundwater resource protection. According to the information collected as well as the results obtained, there are three issues of groundwater salinization that should be well addressed in Penghu. The first is to characterize the mechanism of groundwater salinization in confine and unconfined aquifers, respectively; the second is to identify the attribute of groundwater salinization; the third is to delineate the spatial distribution of the groundwater control zone and the area of groundwater salinization. These issues were solved through two different aspects in this project: field investigation and groundwater modeling. In the field investigation, we sampled 15 wells three times to examine groundwater quality. Our analysis indicated that the potential causes for groundwater salinization can be essentially categorized into three parts: (1) seawater intrusion, (2) the existence of residual ancient brine water, and (3) the calcium ion and magnesium ion released from stratum. To obtain better understanding of the interchange between rain and groundwater, we also performed hydrogen and oxygen isotopic analysis additionally, which is beneficial to assess the recharge source of the groundwater subarea. In reference to remediation strategy, recharge into aquifer is not recommended since there is no sufficient surface water storage, and therefore a decrease in pumping is a better choice. According to the water resource supply and demand, two different remediation strategies were suggested. One is a decrease in pumping by 10%, namely 1,280 m3 per day. The other is a decrease in pumping by 20%, namely 2,558 m3 per day. Two indicators, the annual decrease in seawater intrusion and improvement ratio, were used to quantify remediation efficiency. Our results revealed that the remediation strategy can indeed raise the groundwater level and dilute the seawater intrusion successfully. Moreover, to prevent an increase in water demand during a low-rain year, we also considered the applicability of remediation strategies in high-rain and low-rain years. The result showed that pumping in unconfined aquifer during a low-rain year should be prevented in order to avoid seawater intrusion becoming more serious. To promote the internationalization for Taiwan, we invited two world-renowned scholars who are specialized in water resources to act as keynote speakers in 2016 ICHE (12th International Conference on Hydroscience & Engineering). Furthermore, a special symposium was held in Water Resource Agency in Taichung, which was organized to offer distinguished speeches by four prestigious professors. They shared the experience in water resource and climate change to provide some suggestions and inputs, which is able to serve as the reference for us to make the decision in the future.