設置補注井對於屏東平原沿海地區地層下陷效益探討

Abstract

屏東平原蘊藏豐沛地下水資源，為主要供水來源之一。然因沿海地區及內陸養殖漁業快速發展，造成需水量與地下水超抽量大幅增加，導致屏東平原產生地層下陷及海水入侵等問題。地層下陷與海水入侵引發水災及地下水鹽化等負面影響，威脅民眾生命財產安全。因此，地層下陷問題之防範與整治有其必要性。 為模擬屏東平原沿海地區地層下陷情況與建立後續之整治方案，本研究使用MODFLOW及Interbed子模式建立屏東平原三維地下水流模式及地層下陷模式，進行地層下陷量之模擬。模擬結果顯示屏東平原於未來第5、11及20年之地層下陷量無明顯增加趨勢。此外，以改變含水層儲蓄量比例的方式，模擬氣候變化之情況。模擬結果顯示，於含水層儲蓄量減少比例上升情況下，地層下陷量有顯著增加之趨勢。接著，設置補注井於屏東地層下陷區上游端，分析不同補注量對於含水層之總沉陷量改善效益。並藉由敏感度分析之方式，求解最佳補注井之數量，分析結果顯示，當補注井數量為六口時，有最佳之效益。 最後，建立含水層儲蓄減少變化與影響沉陷量關係式，在有無設置補注井情況下，推估影響極小沉陷量之含水層儲蓄量變化，結果顯示，於未設置補注井之情況下，儲蓄量變化最大百分比為0.055%；有設置補注井時之儲蓄量變化最大百分比為0.297%。上述研究之結果可作為後續政府決策之依據。

Groundwater is abundant in the Pingtung Plain and regarded as the main source for water supply. To meet the water demand of rapid development of aquaculture, over pumping leads to land subsidence and seawater intrusion. These adverse effects result in flooding and groundwater salinity, threating people’s life and property. Therefore, it is necessary to prevent and mitigate the continuing land subsidence. To evaluate the land subsidence in the Pingtung Plain and establish the following mitigation plans, this study aims to simulate the subsidence in this area using Modflow and Interbed. According to the results, no significant increase of land subsidence is observed in the next 5, 11 and 20 years. Furthermore, the condition of climate change is simulated in the function of aquifer storage. The simulation results show that the amount of land subsidence increases significantly when the storage rises. To evaluate the relation between recharge amounts and improvement of subsidence, a set of recharge wells is built in the upstream of the major subsidence area. The optimal number of recharge wells is decided by sensitivity analysis, and the results show that six recharge wells have the best benefit. The relation between decrease of storage amount and subsidence is built under the conditions with and without setup of recharge wells. Subsequently, we can estimate the minimum amount of subsidence in relation with the variation of storage in the aquifer. According to the results, the maximum of decreasing storage percentage is 0.055% without recharge wells and 0.297% with recharge wells。The proposed results can provide the authority to effectively manage the groundwater resource.