結合HEC-RAS與MODFLOW模式評估濁水溪沖積扇地下水位及地層下陷

An Integration between HEC-RAS and MODFLOW to Evaluate Groundwater Level and Subsidence of Aquifers on Choushui River Alluvial Fan

李心惟(SHIN-WEI LEE) ； 葉振峰(CHEN-FENG YEH) ； 李振誥(CHENG-HAW LEE) ； 林宏奕(HUNG-I LIN) ； 龔文瑞(WEN-JUI KUNG)

《台灣水利》 67卷1期 (2019/03) Pp. 91-102

摘要

本研究主要在於結合HEC-RAS執行一維變量流及定量流水理演算，以了解河川水位，作為河川套件之輸入參數，並使用PROCESSING MODFLOW建置濁水溪沖積扇三維地下水流模式，配合IBS1模組理論建構一維地層下陷模式，探討彰化與雲林地區地下水及地層下陷之狀況，以做為地下水流數值與地層下陷模擬分析。透過所建置之濁水溪沖積扇地下水流模式與地層下陷模式，並整合HEC-RAS一維河道水理演算之結果，可以呈現濁水溪的河川水位，作為地下水流模式之河川套件之輸入參數，經地下水流模式驗證結果，指出所建立之地下水流數值模，配合應用IBS1地層下陷模式，可模擬各含水層水位變化與探討地層下陷的狀況。從研究模擬期間之結果推估出濁水溪沖積扇之年平均補注量約19.48億噸，其中年平均地表補注量約10.14億噸，側向補注量約5.7億噸，河川入滲量約3.64億噸。而抽水量部分，以含水層二抽水量最大約每年9.08億噸，濁水溪沖積扇整體抽水量約每年20.83億噸，此結果與前人研究結果相符。同時，應用IBS1地層下陷模式，亦顯示地層下陷情況以含水層二、含水層三最為嚴重，並逐漸從沿海地區延伸至內陸地區，本研究成果可提供未來地區減抽方案模擬與評估，減緩地下水位下降及地層下陷之模式建置參考。

關鍵字

地下水 ； 地層下陷 ； MODFLOW ； IBS1 ； HEC-RAS

並列摘要

Land subsidence caused by over pumping of groundwater resource has severely caused large-scale damage to the Choushui river alluvial fan of the western area in Taiwan. The center of subsidence which has gradually moved inland in recent years will affect the safety of high speed rail and that of other major engineering projects. Therefore, this study uses integrated numerical models to simulate the effect on groundwater level and land subsidence in the study area. The MODFLOW model and INTERBED model with IBS1 modulus are adopted to simulate groundwater flow and land subsidence respectively. Moreover, HEC-RAS is utilized in this study to calculate the stream water level in order to represent groundwater-river interaction in groundwater system with River package. The result shows that the mean recharge of Choushui river alluvial fan is 1.95 billion tons, and the mean surface recharge, lateral recharge and river recharge are 1.01, 0.57 and 0.36 billion tons, respectively. The discharge of Choushui river alluvial fan is 2.08 billion tons, and the maximum discharge is in aquifer two. The discharge is 0.91 billion tons. The groundwater system is still over used during the simulated period. Besides, when an integration among HEC-RAS, MODFLOW and INTERBED models with IBS1 modulus was executed, results indicated that most of the region still has the problem of subsidence in aquifer two and aquifer three on Choushui river alluvial fan. Meanwhile, the subsidence condition is slowing down gradually at the coastal area and instead moving to the inland area. The above result may apply to evaluate groundwater management and reduce the damage from the land subsidence in the study area.

並列關鍵字

Groundwater ； Land subsidence ； MODFLOW ； IBS1 ； HEC-RAS