臺灣地區地下水區水文地質調查及地下水資源評估－地下水補注潛勢評估與地下水模式建置(4/4)

Abstract

水資源的保育是國家重要政策之一，地下水源的保護更是刻不容緩的工作，其中水文地質調查、地下水資源評估、地下水補注機制分析與現地水力試驗與監測則為必要的工作。經濟部自民國80年起，分三期共十七年執行「臺灣地區地下水觀測網整體計畫」，已於臺灣九個地下水區及恒春和澎湖地區，進行水文地質調查研究及地下水觀測井建置工作，並建立完成臺灣地區水文地質基本資料、地下水監測系統、水文地質資料庫及岩心庫等。然而為提高地下水天然補注區範圍劃定及補注量評估之精確度，尚需補充更詳細之地下水層儲水係數、水文地質基本資料及長期地下水水質和水位觀測數據，再結合地下水水位歷線分析，進行地下水補注潛勢評估及建立地下水流數值模式。 本計畫係依據「臺灣地區地下水區水文地質調查及地下水資源評估計畫」（98年至101年）實施進度規劃，進行濁水溪沖積扇及屏東平原地下水區之全區地下水補注潛勢評估與地下水模式建置，並逐年達成下列目標： (1) 建立地下水區全區之地下水補注潛勢評估作業程序。 (2) 完成濁水溪沖積扇地下水主要補注區劃分。 (3) 完成屏東平原地下水主要補注區劃分。 (4) 完成濁水溪沖積扇地下水補注量、抽水量及補注潛勢評估。 (5) 完成屏東平原地下水補注量、抽水量及補注潛勢評估。 本計劃98年度已建立地下水補注潛勢評估標準作業程序，並初步推估出濁水溪沖積扇扇頂地下水補注區之範圍，此範圍與中央地質調查所推測之補注區界線，及本計劃地電阻剖面方法研判之補注區界線範圍結果接近。99年度進一步以98年度建立之地下水補注潛勢評估標準作業程序為基礎，以補注量、硝酸鹽濃度及地電阻值等之空間分佈趨勢，重新檢定調整補注潛勢因子之權重，檢討修訂地下水補注潛勢評估標準作業程序，完成濁水溪沖積扇地下水主要補注區之劃分。並完成濁水溪沖積扇數值模式建置，以推估全區之抽水量與其分布及平原與側向之補注量。100年度(本年度)將建立屏東平原地下水區之全區地下水補注潛勢評估及主要補注區劃分，並完成穩態地下水數值模式建置。 本計畫整個完成後所得成果可供主管機關劃定地下水水源保護區之依據，並可藉此對保護區土地利用及水土污染防治提出適當的管制辦法，提供地下水資源永續經營管理的基礎。

Groundwater resource protection is an emergency task for water resources conservation in Taiwan. The hydrogeological investigation, groundwater resources evaluation, groundwater recharge estimation, groundwater field experiment and monitoring are all important works to protect the groundwater resources. To facilitate the groundwater management, Ministry of Economic Affairs in Taiwan had established a national groundwater monitoring network since 1991 to 2008. The accomplishment of groundwater monitoring network had established a data base system with large amount of hydrogeological data, and the core samples from geological logging were also collected and inventoried. Nevertheless, to increase the accuracy of high groundwater recharge area assessment and recharge rate estimation. More hydrogeological information such as aquifer storage coefficient and long term monitoring data of groundwater level and quality are necessary. Beside data requirement, more research work such as groundwater level analysis, groundwater recharge potential assessment and groundwater model simulation are also essential. Following the project of ‘Hydrogelogical investigation and groundwater resources assessment plan in Taiwan’, this project is to define the high groundwater recharge area in Choshuichi groundwater basin and Pintung plain, and develop numerical simulation models for both area. Precisely, following subjects will be accomplished within the project period from 2009 to 2012. (1) Establishing the standard procedure of groundwater recharge potential assessment. (2) Defining the high groundwater recharge area in Choshuichi groundwater basin. (3) Defining the high groundwater recharge area in Pintung plain. (4) Investigating the groundwater recharge potential, recharge rate and pumping rate in Choshuichi groundwater basin. (5) Investigating the groundwater recharge potential, recharge rate and pumping rate in Pintung plain. By year of 2009, this study has established a standard procedure for assessing groundwater potential recharge and sketched out the potentially high recharge area in Choshuichi groundwater basin. The primary estimation of high groundwater recharge area is closed to that estimated by the ‘Central Geological Survey’. It is also similar to that measured in this project by another method, resistivity image profiling. For the coming year (2010), following the results of 2009, the assessing procedure of potentially high recharge area will be refined basing on the areal recharge rate estimation, nitrate concentration distribution and contour map of one dimensional resistivity data. The high groundwater recharge area in Choshuichi groundwater basin will also be defined in 2010. Beside, a transient groundwater simulation model will be developed using MODFLOW package. The simulation model will be used to estimate the regional pumping rate and groundwater recharge from areal and boundary. The result of this project can provide a valuable reference to define a groundwater protection area and facilitate to propose a regulation practice for groundwater conservation and contamination prevention, and proving a basis for achieving groundwater sustainable management for the basin.