台灣本島年降雨量豐沛,卻存在時空分配不均的情況,因此常造成水資源需求供需失調,致使部分地區以抽取地下水來彌補不足之用水需求。過量抽取地下水之行為,會造成地下水水位急速下降及導致地層下陷與海水入侵等問題,位於台灣南端的屏東平原亦面臨此等問題。 本研究採用PMWIN地下水流數值模擬模式來模擬屏東平原之地下水流況,此軟體為整合美國地質調查所發展之MODFLOW地下水流模式,進而研發成的視窗版軟體:MODFLOW模式以有限差分法的數值求解方法來進行擬三維地下水流問題的模組化軟體,台灣地區亦有使用此模式於地下水管理及規劃之經驗。本研究蒐集2009年至2011年屏東平原的地下水位觀測水位、降雨與相關的水文地質參數資料等,進行屏東平原之地下水流數值模擬,模擬中根據地質概況將地層概分成五個概念化含水層。研究範疇為以海拔100公尺以下之沖積平原為主,模擬區域北側、西側及東側皆設定為零流量邊界,南側臨海部份則設定為定水頭邊界。研究中除考慮降雨補注與各區域抽水外,並考慮河川地表水體與地下水體之交換,以及上游側流量等條件,據以進行屏東平原之地下水數值模擬。 當完成區域內地下水水位觀測資料與模式模擬水位資料之擬合,本研究即可推估各區域之抽水量時空變化及完成水收支平衡分析。由模擬時間(2009~2011)之水收支平衡分析得知,屏東平原地下水年平均抽水量約為14.14億噸;河川流入地下水年平均約為6.83億噸、地下水流入河川年平均約為4.29億噸;上游邊界側流量年平均約為0.58億噸;降雨入滲年平均約為7.86億噸,雨水補注約佔總補注量的39%。 本研究同時以地下水管理指標(Groundwater management index, GMI)定義安全水位、下限水位及嚴重下限水位。依據研究區域內之觀測井自民國89年至100年之水位訂定對應之安全、下限及嚴重下限水位門檻數值,可做為屏東平原地下水管理之依據。
There is abundant rainfall in Taiwan, but the distribution varies in space and time, that bring about the imbalance of supply and demand of water resources. In order to cover the shortage, some areas had to overpumping groundwater. That will cause the problems of groundwater levels fall and land subsidence and saline water intrusion in Pingtung Plain at southern Taiwan. In this study was simulated the groundwater resources and to description and prediction of the behavior of groundwater system in the Pingtung Plain by the code MODFLOW, which is a modular three-dimensional finite difference groundwater model of U.S, Geological Survey. There was used in management and planning of groundwater resources in Taiwan. This study collected the observation levels and the rainfall and the hydrogeologic parameter of groundwater in Pingtung Plain from 2009 to 2011, and numerical simulation of groundwater. This study area was alluvial plain from under the 100 meters above sea level. In addition to rainfall recharge and pumping, the study consider the water exchange between surface and underground, and the side flow from upstream. When we finish the numerical simulation of groundwater, we could get the solution of this groundwater system, that display the average amount of pumping is the value of 14.14×108 m3 per year, and the average amount of lateral recharge is the value of 0.58×108 m3 per year, and the average amount of rainfall recharge is the value of 7.86×108 m3 per year in Pingtung Plain from 2009 to 2011. In this study, we delimit the security level, lower level, lower critical level of this groundwater system by the Groundwater management index, GMI. That could be use to manage the groundwater in Pingtung Plain.