雲林濱海地區地下水水文特性初探

本文研究雲林濱海地區之麥寮園區係填海造陸基地，屬於雲林離島式基礎工業區之一部分，是一採離島式開發之濱海新生地，園區除了地下水水質的定期監測外，鑑於地下水水文資料是水質預警監測因應之基礎資訊，遂於2010～2017年，利用全區域既設地下水監測井網，分階段自主推動園區內地下水水文之基本調查研究，以應用於地下水污染防治工作做預防性準備，除透過文獻蒐集瞭解區域水文地質資訊，對於地下水水文調查，則是藉由長期連續性的地下水水位觀測，分析地下水流場。自2010年開始，園區利用全區域既設地下水監測井網，藉由分階段加密地下水水位調查點位的方式，規劃以自記式水位計每0.5小時之觀測頻率，收錄長期地下水水位連續觀測資料。本文主要利用此等重要資料，作為印證離島式新生地地下水流場是否符合Ghyben and Herzberg理論之重要基礎，及瞭解地下水流場變化情形。本文研究顯示，麥寮園區以海域平均海平面為海側邊界，地下水流方向主要受水力梯度驅動，大致上從中央水位最高處呈輻射狀向四周外圍流出入海，島嶼型地下水之淡水分布近似於凸透鏡體，懸浮於下方楔型海水楔上，符合Ghyben and Herzberg理論，藉由分階段加密方式，地下水流場解析度逐步提升後，局部區域流向可能因地質異質性或受地下結構物影響產生繞流現象，然經局部繞流後其流場最終仍同大區域流場特性呈中央往四周流動。

關鍵字

填海造陸；離島式新生地；地下水水位連續觀測；地下水流場； Ghyben and Herzberg理論

並列摘要

Mailiao Industrial Complex is located in the offshore industrial zones in Yunlin County, with the intent of reclamation for constructing an oil refinery plant. In addition to the regular monitoring of groundwater quality in Mailiao Industrial Complex, since groundwater hydrological data is the basic information needed for water quality early warning and monitoring, Formosa Plastics Corporation built a groundwater monitoring well network throughout the region during 2010-2017. Phased Investigation Plan was used to promote the basic investigation and research of groundwater hydrology in Mailiao Industrial Complex, thereby allowing preparation for the prevention and control of groundwater pollution. In addition to using regional hydrogeological information obtained through literature collection, groundwater hydrological surveys use long-term continuous groundwater level observations to analyze groundwater flow fields. From 2010-2017, Mailiao Industrial Complex used the existing groundwater monitoring well network throughout the region, with self-recording level gauges measuring water levels every 0.5 hr to collect long-term continuous groundwater level data. This research mainly uses the survey data of groundwater levels in Mailiao Industrial Complex as the basis for confirming whether the groundwater flow field of the outlying islands conforms to the Ghyben and Herzberg theory and for understanding the changes of the groundwater flow field. This study shows that Mailiao Industrial Complex uses the average sea level as the seaside boundary, and that the direction of groundwater flow is mainly driven by hydraulic gradients. Groundwater generally flows out into the sea, radiating from the highest point of the central water level to the periphery. The freshwater distribution of island-type groundwater is similar to a convex lens body suspended on a wedge-shaped denser body of saltwater, in line with the Ghyben and Herzberg theory. Moreover, the resolution of the groundwater flow field can be gradually improved by means of phased encryption. Although the local flow direction may be affected by geological heterogeneity or the influence of underground structures, the flow direction eventually radiates from the center to the surroundings after these local detours.