利用熱示蹤劑試驗與水-熱數值模式評估海岸帶含水層分層流動特性─ 以桃園海岸帶場址為例;Utilization of in-situ thermal tracer tests and hydro-thermal model to characterize the stratified aquifer systems- a case study in the Taoyuan coastal area

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Title:	利用熱示蹤劑試驗與水-熱數值模式評估海岸帶含水層分層流動特性─ 以桃園海岸帶場址為例;Utilization of in-situ thermal tracer tests and hydro-thermal model to characterize the stratified aquifer systems- a case study in the Taoyuan coastal area
Authors:	許安誼;Hsu, An-Yi
Contributors:	應用地質研究所
Keywords:	跨孔熱示蹤劑試驗;海岸帶地下水出流量;三維數值模式;桃園西部沿海;Cross hole heating test;Numerical simulation analysis;Submarine groundwater discharge;Western Taoyuan Coast
Date:	2024-07-30
Issue Date:	2024-10-09 17:23:12 (UTC+8)
Publisher:	國立中央大學
Abstract:	隨著沿海地區經濟日益發展，海岸環境退化的問題逐漸浮現。為改善此現象，了解沿海含水層與海水間動態交換的過程，必是後續管理及規劃沿海含水層不可或缺的一環。本研究透過現地熱示蹤劑試驗結合三維數值模擬，比較不同方法所估算之海岸帶地下水出流量(Submarine groundwater discharge)差異，探討沿海含水層分層流動機制。為獲取此地分層流動和熱能傳遞特性，本研究先於此地進行水力試驗及熱示蹤劑試驗，後運用MODFLOW和MT3DMS兩種數值模式，模擬出海淡水交互作用對沿海含水層的動態影響。此研究地點位於中央大學TaiCOAST臨海觀測站，模式將透過現地蒐集之地下水位和溫度觀測資料進行率定驗證。現地試驗結果顯示，熱示蹤劑試驗所產生的熱響應與鑽探岩心匹配，此外加熱井附近的觀測井，從地下水面到深12公尺間皆有些微之熱反應。數值模擬結果與觀測資料吻合，以流場模擬所計算之比出流量範圍介於0.03至0.12(m/day)之間，結果顯示深度0至7公尺及26至50公尺整體比出流量較高，高低潮位所造成的比出流量差異達0.03(m/day)以上；深度12至26公尺整體比出流量較低，高低潮位所造成的比出流量差異僅0.004(m/day)。而以模擬熱示蹤劑試驗所得到的溫度峰值傳遞時間差異計算出各剖面的垂直通量，得出地下水通量大致介於2.5m/day至5m/day，與前期研究所求得之加熱井通量相似，且符合前期研究認為熱示蹤劑試驗所適合估算之比出流量範圍。地下水流場及熱示蹤劑試驗所模擬之溫度場，由於資料尺度及方法不同，導致所計算出之地下水比流量存在大約兩個數量級之差異，此結果表明桃園西部沿海之海岸地下水出流量豐沛，透過此研究了解此地區沿海含水層分層流動之特性。;With the increasing economic development in coastal areas, the problem of coastal degradation has emerged. To facilitate subsequent planning of water resources management, it is essential to determine the coastal aquifer′s dynamic exchange with the ocean. In this research, our objective is to integrate innovative experiments and modeling techniques to discuss the submarine groundwater discharge(SGD), which is estimated by different methods, aiming to clarify the layered flow mechanisms in coastal aquifer system. Specific hydraulic and heat tracer tests are conducted at this location to obtain the flow rate and heat transfer characteristics of the layered flow. In subsequent steps, we employed the MODFLOW and MT3DMS numerical models to simulate the influence of interactions between seawater and groundwater on the temperature field of the coastal aquifer. The calibration of the model is based on the groundwater levels and the temperature acquired from monitoring wells which installed near the coastline at the TAICOAST observation station. The experimental results show that the thermal responses from the active heat tracer test can match with the core sample. Significant thermal responses are observed vertically in the observation well near the heating well, ranging from the groundwater level to depths of 12 m, with BW08 being the observation well showing the maximum thermal responses. The simulation of numerical model aligns well with the observed groundwater levels and temperature in wells, with the specific discharge calculated from flow field simulations ranging from 0.03 to 0.12 m/day. The results indicate higher specific discharge at depths from 0 to 7 meters and 26 to 50 meters, with tidal variations causing differences of over 0.03 m/day. In contrast, lower specific discharge was observed at depths from 12 to 26 meters, with tidal variations causing differences of only 0.004 m/day. Using the time differences in temperature peak transmission obtained from simulated heat tracer tests, the vertical fluxes for different profiles were calculated, yielding groundwater fluxes ranging from approximately 2.5 to 5 m/day. These findings are consistent with the fluxes obtained by pervious study from heated wells and align with the specific discharge range suggested by pervious study for heat tracer tests. The groundwater flow field and the temperature field simulated by the heat tracer tests showed a discrepancy of about two orders of magnitude in the calculated specific discharge due to differences in data scales and methods. These results indicate that the coastal groundwater discharge in western Taoyuan is abundant, providing insights into the layered flow characteristics of the coastal aquifer in this area.
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