桃園台地地下水數值模擬及 管理水位之探討

台灣本島降雨量豐富，卻存在著時空分布不均的情形，由於降雨量分布不均，外加河川流短坡陡，河川流量迅速流入海裡，使得地面水源之運用極為困難。地下水不但水量充沛且因位於地底，不易受到汙染，故水質優良，由於地面水體較容易受到污染而影響其可利用性，在地面水供應不足情況下，地下水資源常成為支應地面水之水源來源。本研究採用PMWIN地下水數值模擬模式來模擬桃園台地之地下水水流狀況。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。本研究蒐集2016年至2020年桃園台地的地下水觀測水位、降雨資料與相關水文地質概況，進行桃園台地之地下水水流數值模擬，模擬中將地層概分為四個含水層，東側、南側、北側分別為零流量邊界，西側則設定為定水頭邊界。另考慮研究時間內之降雨補注與各地區抽水。當區域內地下水之觀測水位與模擬水位擬合後，即可推估桃園台地近年地下水之抽水、補注等各項分析。分別利用水文分析與數值模擬來探討出未來可調動水量，以平均水位減一倍標準差為安全水位時，經水文分析出第一、二層可調度水量為0.61億噸及1.63億噸；用數值模擬方式可得桃園地區第一、二層地下水抽水量分別為0.52億噸及0.69億噸後各測站將會下降至安全水位。以平均水位減二倍標準差為安全水位時，第一、二層可調度水量為0.99億噸及2.06億噸；用數值模擬方式可得知桃園地區第一、二層地下水抽水量分別為1.02億噸及1.4億噸後各測站將會下降至安全水位。

關鍵字

地下水；數值模型； PMWIN ；水位管理；安全出水量

並列摘要

Taiwan has abundant rainfall, but there is uneven distribution in time and space. Due to the uneven distribution of rainfall, coupled with the short and steep slopes of rivers, the flow of rivers quickly flows into the sea, making the use of surface water sources extremely difficult. Groundwater is not only abundant in water, but also is located underground and is not easily polluted, so the water quality is excellent. Because surface water is more susceptible to pollution, its availability is affected. When the supply of surface water is insufficient, groundwater resources often become the source of water that supports surface water. In this study, the PMWIN groundwater numerical simulation model was used to simulate the groundwater flow conditions in the Taoyuan Tableland. This software is a Windows version software developed by integrating the MODFLOW groundwater flow model developed by the US Geological Survey. In this study, the groundwater observation level, rainfall data and related hydrogeological profiles of the Taoyuan Tableland from 2016 to 2020 were collected, and the groundwater flow numerical simulation of the Taoyuan platform was carried out. The neumann boundary is set to the north 、east、 south, and the Dirichlet boundary is set to the west. In addition, the rainfall replenishment and water pumping in each area during the study period are also considered. After the observed water level of groundwater in the area is fitted with the simulated water level, various analyses such as pumping and refilling of groundwater in Taoyuan Terrace in recent years can be estimated. Hydrological analysis and numerical simulation are used to discuss the future adjustable water volume. When the average water level minus one standard deviation is taken as the safe water level, the hydrological analysis shows that the first and second floors can be dispatched water volume of 61 million tons and 163 million tons; According to the numerical simulation method, the groundwater pumping volume of the first and second layers in Taoyuan area is 52 million tons and 69 million tons, respectively, and each station will drop to the safe water level. When the average water level minus twice the standard deviation is taken as the safe water level, the water volumes that can be dispatched on the first and second floors are 99 million tons and 206 million tons; by numerical simulation, it can be known that the groundwater pumping volumes of the first and second floors in Taoyuan area are 1.02 million tons, respectively. After 100 million tons and 140 million tons, the stations will drop to the safe water level.