非拘限砂質海岸含水層中潮汐和沙灘坡度水文動力條件影響苯傳輸;Hydrodynamic influences of tidal fluctuations and beach slopes on benzene transport in unconfined,sandy coastal aquifers.

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Please use this identifier to cite or link to this item: http://ir.lib.ncu.edu.tw/handle/987654321/54034

Title:	非拘限砂質海岸含水層中潮汐和沙灘坡度水文動力條件影響苯傳輸;Hydrodynamic influences of tidal fluctuations and beach slopes on benzene transport in unconfined,sandy coastal aquifers.
Authors:	魏意銘;Wei,Yi-Ming
Contributors:	應用地質研究所
Keywords:	漏油事件;BTEX;HYDROGEOCHEM;沿海含水層;潮汐變化;海灘坡度;鹽楔;BTEX;Beach slopes;Saltwater wedge;Tidal fluctuation;Estuary aquifers;HYDROGEOCHEM;Oil spills event
Date:	2012-07-26
Issue Date:	2012-09-11 18:26:38 (UTC+8)
Publisher:	國立中央大學
Abstract:	當海上油洩漏事件發生後，油污會受洋流、風、潮汐等因素，飄移至陸地沿岸並造成汙染，進而會影響沿岸生態環境和人類遊憩生活。對於油污染的鑑定指標，最常見的方法是檢測BTEX(Benzene、Toluene、Ethylbenzene、Xylenes)的存在與否。其中苯(Benzene, C6H6)為BTEX中最具毒性的致癌物質，此物質可能會威脅沿岸生態系統和危及人類健康。因此，瞭解苯在沿海含水層中的傳輸過程，尤其是含水層的水文地質條件差異，對於預測污染區域、應變處理以及整治規劃是非常重要的參考依據。本研究使用HYDROGEOCHEM數值模式模擬垂直二維沿岸含水層之苯污染物傳輸情形。考慮2010年油洩漏事件中，受到油污染影響的阿拉巴馬州鮑德溫縣(Baldwin Country)作為研究區域，模擬區域為一長度1100公尺，深度100公尺之沿岸含水層。本研究的目的為量化潮汐變化和地形坡度兩種含水層水文地質條件，以及其間的相互作用，對於苯污染物在海灘內部傳輸的影響。透過微幅修改HYDROGEOCHEM邊界輸入條件及變形網格，該模式可以合理地反應潮汐與坡度條件下的苯污染物傳輸。模擬結果顯示有潮汐變動下，漲退潮期間會在靠近海灘斜坡下出現上部鹽分區；這小循環流將局限苯污染團向內陸移動距離，但小循環流會將污染團帶至含水層深處，苯污染範圍將和此小循環流大小相關，小循環流的大小取決於海岸線的潮汐振幅和海灘坡度。模擬結果顯示在現地條件下，當潮汐振幅增大1倍，則苯污染團向陸地移動40公尺，垂直深度增加20公尺。而海灘坡度增加3倍，苯污染團向陸地移動50公尺。模擬結果亦表明海灘坡度變陡，苯污染團自淨能力強，潮汐振幅增大，自淨能力弱；在坡度最緩且潮汐振幅最大的狀況下，苯污染團將最難以清除。本研究將模擬結果應用於現地海岸地形條件，其結果顯示鹽楔朝向陸地距離與苯污染團的深度，在現地油汙染發生後，凸岸污染輕微和凹岸污染嚴重呈正相關。Oil will polluted the coastal area by ocean current,wind, tide or other factors after oil spills from ocean. Moreover, the oil on the coastal area will affected ecosystem environment and people amusement life. The concentration of the BTEX is the index to identify the degree of oil pollution. Benzene, as one of the BTEX compounds, is recognized to be carcinogenicity and high toxicity. It may threat coastwise ecosystem and human health. Therefore, the understanding of benzene transport behavior in costal aquifers is important for predictions of contaminated zones, organization of emergency treatment and designs of remediation plans. This study employs the HYDROGEOCHEM numerical model to simulate two-dimensional benzene pollutants transport procedures in estuary aquifers. A profile estuary aquifer with 1100m in length and 100m in depth in Baldwin County, Alabama, which been polluted in 2010 oil spill event, is considered as study area in the illustrated examples. The objection of this study is to quantify the influence of benzene transport under hydrogeological conditions of tidal fluctuations and beach slopes. With the change of model mesh and modification of boundary condition in HYDROGEOCHEM, the model rational response benzene pollution under tidal fluctuations and beach slopes. Simulation results show that tidal fluctuations will lead to upper saline plume (USP) near the ground surface of the beach slope. Such local circulation flows will trap benzene plume to move toward the land. However, the plume may migrate to deeper aquifers. The sizes and location of benzene plume are highly relevant to the local circulation flows, and the behavior of local circulation flows depends on the effects of tidal amplitudes and surface slopes along coastal lines. Base on the field-scale conditions, results show that a doubled tidal amplitude increasing will lead to the increased plume size with 40m in length and 20m in depth. Additionally, a tripled beach slopes will lead to 50m plume movement toward the land. Simulation results also show that steep beach slopes will enhance self purification (clean) of benzene plumes. The most severe condition is that the large tidal amplitude and small slopes will cause a long self purification (clean) time for benzene plume. This study then employed the simulation results to apply to field-scale coast topographic conditions. The results show that the distance of saltwater wedges and the depth of benzene plumes exists a positive correlation between shapes of coastal lines.
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