新竹尖石地下水流徑綜合研判

A comprehensive study of groundwater flow path in Jianshih well field

朱怡姿(I-tzu Chu)

指導教授 ： 蔡龍珆

國立中央大學/地球科學學院/應用地質研究所/碩士(2011年)

摘要

臺灣平均年降雨量約為2500毫米，但是伴隨著季節、地點與高程的不同，降雨量也隨之變化，又因地形陡峭以至於水不易儲存，若能推估準確且合理之補注來源，不但能有效應用地下水資源及避免資源耗竭，亦可瞭解地下水之逕流補注機制。本研究於2010年6月至2011年5月進行新竹縣尖石地區之裂隙岩層試驗井場地下水、河水、山溝滲水及雨水樣本採集，以氫氧同位素與水化學之主要陰陽離子分析其水文地化特性，考慮區域地質背景、水文狀況及時空變異之演化過程；以地理資訊系統整合前人觀測資料用以探討2008 ~ 2011年間之地下水流徑和入滲來源，藉此釐清尖石井場之水位流場控制因素，據以評估地下水水文地化特性的時空域分布。研究結果顯示小雨期地下水同位素值較重，說明降雨量較少則同位素組成偏重，而地表水在大小雨期都均勻分布在天水線附近，表示補注來源為雨水且受分化與蒸發效應不大；水位觀測資料可看出大小雨期之水位差異不大，可能是受到山溝與河水補注之影響；以水化學顯示水質偏弱鹼性，在2010年10 ~ 11月Well W-2表現為第三型水體，指出地下水在地層停留的時間較久，釋出鹼土金屬與硫酸根離子。尖石井場之氫氧同位素顯示大小雨期井場之地下水流向受到山溝補注，而部分井場地下水則有受到河水側向補注，在小雨期Well W-1受河水補注較為明顯。

關鍵字

氫氧同位素 ； 水化學 ； 地下水補注

並列摘要

Average annual precipitation is about 2500 millimeters in Taiwan. It varied with difference in season, location and elevation. Water storage is especially difficult in steep terrain areas. In order to promote effective application and avoid depletion of groundwater resources, rational evaluation and management of groundwater are needed in achieving accurate and reasonable estimation of groundwater resources. In this study, water samples were collected monthly from June 2010 to May 2011 in Jianshih well field and nearby areas. Surface water samples were taken from gullies and rivers, groundwater samples were taken from wells. hydrogen and oxygen stable isotopes as well as major cations and anions were analyzed, so as to evaluate their temporal and spatial variations in geochemical characteristics. Furthermore, integration of geographic information systems plus previous studies of groundwater flow from 2008 to 2011 in Jianshih area, the controlling factors of groundwater hydrology and geochemical characteristics can also be examined. The results show that the isotopes of groundwater are heavier in the low-ppt season. Additionally, surface water are evenly distributed near MWL both in hi-ppt and low-ppt season, which implied the source of recharge was not subjected to differentiation and evaporation; Besides the influence of precipitation, no significant change in water table can be observed. According to hydrochemical data, most of the groundwater in the well field exhibit weak alkaline whereas Well W-2 shifted to type III (alkaline-earth, non-bicarbonate) in October and November of 2010, probably due to the release of alkaline-earth metals and sulfate after a long residence time of groundwater. Finally, recharge source of groundwater was calculated by the mass balance from oxygen and hydrogen isotopes. In conclude, gully water and river water are the main sources contributed into the well field both in high and low precipitation seasons. The contribution of river water is especially noticeable at well W-1 during low-ppt season.

並列關鍵字

hydrogeochemistry ； hydrogen and oxygen isotope ； groundwater

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