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題名 | 七股潟湖沙洲變遷對潟湖水體交換能力影響之數值研究=A Numerical Study on Sandbar Migration Subject to Water Exchange Capacity in Cigu Lagoon |
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作者 | 林鼎傑; 劉景毅; 蕭士俊; | 書刊名 | 海洋工程學刊 |
卷期 | 15:3 2015.09[民104.09] |
頁次 | 頁137-154 |
分類號 | 351.3 |
關鍵詞 | 七股潟湖; 沙洲; 地形變遷; 海水交換; 牡蠣養殖; Cigu lagoon; Sand barrier; Morphology; Tidal exchange; Oyster culture; |
語文 | 中文(Chinese) |
中文摘要 | 本文建構二維淺水波及擴散傳輸模式,針對2012年與2015年七股潟湖沙洲變遷後,對於潟湖內水動力及水體交換能力之影響進行數值研究。研究結果指出,2015年網仔寮汕與青山港汕已經再度合併,兩者間之潮口已經消失;網仔寮汕南側/頂頭額汕北側分別產生淤積/侵蝕之現象,造成網仔寮汕往南延伸及頂頭額汕往南退縮,兩者間之潮口因此南移。水動力計算結果顯示,以2012年潟湖實測地形為基準,2015年沙洲變遷後,潟湖內最大流速仍舊以網仔寮汕與頂頭額汕潮口區域為最大,約在0.5 m/s之間;網仔寮汕南側水域與頂頭額汕北側水域因為沙洲南移,最大流速與淨流速分別降低與增加,也導致潮口處水體交換能力較佳之位置南移。水體交換能力計算結果指出,2015沙洲變遷後仍舊以南側潮口區域為最佳,其局部滯留時間(LRT)尺度為O(數小時),逐漸地往潟湖內部遞增,尺度約在O(1~2)天左右,交換能力佳;然而網仔寮汕與青山港汕間的潮口已經封閉,LRT至少大於16天。潮汐交換率(TER)結果與LRT類似,仍以南側潮口處為最佳,約在15%左右,然而潟湖北側區域因潮口封閉導致TER幾乎消失。整體而言,在16天的潮汐作用下,2015年潟湖內整體稀釋能力相較於2012年而言下降了約50%。本文最後並提出3個潟湖內養殖牡蠣與海水交換能力之相關議題,作為後續研究之依據。 |
英文摘要 | Water exchange capacity subject to sandbar migration between 2012 and 2015 in Cigu lagoon is investigated using a two-dimensional shallow water and transport model. The results indicate that (1) Wan-Zi-Liao (WZ) and Chin-Shan-Kang (CS) sandbars have been merged, (2) the inlet between WZ and CS has been vanished. The erosion and deposition are observed nearby the southern part of WZ and northern part of Ding-To-A (DT) sandbars, thereby causing the inlet migrated southward. Comparing to the bathymetry in 2012, the maximum velocity field with an order of 0.5 m/s subject to sandbar migration in 2015 is observed as that in 2012 nearby the inlet between WZ and DT. However, computed residual flow suggests that the flow velocity decreases and increases in the southern part of WZ and northern part of DT, implying a water exchange capacity become better in the northern part of DT. Numerical results exhibit that LRT is around an order of O (hour) nearby the inlet of WZ and DT; LRT gradually increase toward the inner lagoon with an order of O (1 ~ 2 days). Unfortunately, the LRT is at least larger than 16 days in inner lagoon because of the close of inlet between WZ and CS. LRT and TER exhibit similar phenomena. Generally, an overall dilution capability subject to lagoon bathymetry in 2015 decreases around 50% comparing to that in 2012. Three import topics on oyster rack and water exchange for future study are also reported. |
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