潮汐不對稱是指當潮汐由深海傳遞至近岸時，因水深變淺或地形變化，使得非線性效應放大，衍生出高頻率或低頻的天文分潮，在不同頻率的分潮疊加下所產生漲退潮延時、流速以及峰值水位不對稱的現象。臺灣西部地勢平緩，河川下游多屬感潮河段，在河川逕流潮汐、波浪的交互作用下，潮汐不對稱現象將會更加明顯。
本研究使用Delft3D-FLOW模擬曾文溪河道及沿岸水動力條件，並透過調和分析解析模擬範圍內天文潮分潮的振幅及相位角以估算潮汐不對稱特性，結果顯示現況曾文溪河道上游處為漲潮主導，越往下游隨著潮汐不對稱性偏度降低則逐漸轉變為退潮主導。沿岸部分以曾文溪河口為界，河口以南呈現退潮主導，以北則為漲潮主導。而河川流量效應會使M4分潮振幅成長，進而增加曾文溪河道內潮汐不對稱偏度，使得潮汐不對稱特性會往漲潮主導方向發展。此外，河道內M2及其倍頻分潮M4或M6的疊合，除了會使漲退潮延時不對稱之外，也會影響到最大漲退潮流速，進而減緩或加快物質傳輸速度。

This study mainly used the Delft3D-FLOW to simulate the coastal hydrodynamics of the Zengwen River estuary and the surrounding nearshore areas. Tidal harmonic analysis was applied to analyze the amplitude and phase of tidal constituents and the corresponding tidal asymmetry skewness. The results indicated that the upstream area of the Zengwen River was mainly flood dominant; the decrease of tidal asymmetry skewness downstream of the Zengwen River area contributed to gradual ebb dominant. The north coast of the Zengwen River estuary is flood dominant, while the south coast of the estuary is ebb dominant. The increase of river discharge affects M4 development, increasing the tidal asymmetry skew-ness of the Zengwen River itself and making it more flood dominant. When M2 overlaps with M4 and M6 of specific higher frequencies, the flood and ebb times and flow rates are affected, possibly affecting sediment transportation in the estuary area and river channel.

1. Blanton, J. O., Lin, G., Elston, S. A. (2002). Tidal current asymmetry in shallow estu-aries and tidal creeks. Continental Shelf Research, 22(11-13), 1731-1743.
2. Bolle, A., Wang, Z. B., Amos, C., De Ronde, J. (2010). The influence of changes in tidal asymmetry on residual sediment transport in the Western Scheldt. Continental Shelf Research, 30(8), 871-882.
3. Cai, H., Savenije, H., Toffolon, M. (2014). Linking the river to the estuary: influence of river discharge on tidal damping. Hydrology and Earth System Sciences, 18(1), 287-304.
4. Cai, H., Savenije, H. H., Yang, Q., Ou, S., Lei, Y. (2012). Influence of river discharge and dredging on tidal wave propagation: Modaomen Estuary case. Journal of Hydrau-lic Engineering, 138(10), 885-896.
5. Deltares. (2018a). Delft3D-FLOW user manual. Deltares Delft, The Netherlands.
6. Deltares. (2018b). Delft3D-WAVE User Manual. Deltares Delft, The Netherlands.
7. Gallo, M. N., Vinzon, S. B. (2005). Generation of overtides and compound tides in Amazon estuary. Ocean Dynamics, 55, 441-448.
8. Gong, W., Schuttelaars, H., Zhang, H. (2016). Tidal asymmetry in a funnel-shaped es-tuary with mixed semidiurnal tides. Ocean Dynamics, 66, 637-658.
9. Guo, L., van der Wegen, M., Jay, D. A., Matte, P., Wang, Z. B., Roelvink, D., He, Q. (2015). River‐tide dynamics: Exploration of nonstationary and nonlinear tidal behavior in the Y angtze R iver estuary. Journal of Geophysical Research: Oceans, 120(5), 3499-3521.
10. Guo, L., Van der Wegen, M., Roelvink, J., He, Q. (2014). The role of river flow and tidal asymmetry on 1‐D estuarine morphodynamics. Journal of Geophysical Research: Earth Surface, 119(11), 2315-2334.
11. Guo, L., van der Wegen, M., Wang, Z. B., Roelvink, D., He, Q. (2016). Exploring the impacts of multiple tidal constituents and varying river flow on long‐term, large‐scale estuarine morphodynamics by means of a 1‐D model. Journal of Geophysical Research: Earth Surface, 121(5), 1000-1022.
12. Guo, L., Wang, Z. B., Townend, I., He, Q. (2019). Quantification of tidal asymmetry and its nonstationary variations. Journal of Geophysical Research: Oceans, 124(1), 773-787.
13. Haigh, I. D., Eliot, M., Pattiaratchi, C. (2011). Global influences of the 18.61 year nod-al cycle and 8.85 year cycle of lunar perigee on high tidal levels. Journal of Geophysi-cal Research: Oceans, 116(C6).
14. Hoitink, A., Hoekstra, P., Van Maren, D. (2003). Flow asymmetry associated with as-tronomical tides: Implications for the residual transport of sediment. Journal of Geo-physical Research: Oceans, 108(C10).
15. Horrevoets, A., Savenije, H., Schuurman, J., Graas, S. (2004). The influence of river discharge on tidal damping in alluvial estuaries. Journal of Hydrology, 294(4), 213-228.
16. Kowalik, Z., Murty, T. S. (1993). Numerical modeling of ocean dynamics (Vol. 5): World Scientific.
17. Lafta, A. A. (2022). Investigation of tidal asymmetry in the Shatt Al-Arab river estuary, Northwest of Arabian Gulf. Oceanologia, 64(2), 376-386.
18. Li, L., Wang, X. H., Williams, D., Sidhu, H., Song, D. (2012). Numerical study of the effects of mangrove areas and tidal flats on tides: A case study of Darwin Harbour, Australia. Journal of Geophysical Research: Oceans, 117(C6).
19. Matte, P.,Secretan, Y.,and Morin, J. (2014). Temporal and spatial variability of tidal‐fluvial dynamics in the St. Lawrence fluvial estuary: An application of nonstationary tidal harmonic analysis. Journal of Geophysical Research: Oceans, 119(9), 5724-5744.
20. Matte, P., Secretan, Y., Morin, J. (2017). Hydrodynamic modeling of the St. Lawrence fluvial estuary. I: Model setup, calibration, and validation. Journal of Waterway, Port, Coastal, and Ocean Engineering, 143(5), 04017010.
21. Nidzieko, N. J. (2010). Tidal asymmetry in estuaries with mixed semidiurnal/diurnal tides. Journal of Geophysical Research: Oceans, 115(C8).
22. Pawlowicz, R., Beardsley, B., Lentz, S. (2002). Classical tidal harmonic analysis in-cluding error estimates in MATLAB using T_TIDE. Computers & Geosciences, 28(8), 929-937.
23. Pugh, D., Woodworth, P., (2014). Sea-level science: Understanding tides, surges, tsu-namis and mean sea-level changes. Cambridge University Press.
24. Ranasinghe, R., Pattiaratchi, C. (2000). Tidal inlet velocity asymmetry in diurnal re-gimes. Continental Shelf Research, 20(17), 2347-2366.
25. Sekovski, I., Armaroli, C., Calabrese, L., Mancini, F., Stecchi, F., Perini, L. (2015). Coupling scenarios of urban growth and flood hazards along the Emilia-Romagna coast (Italy). Natural Hazards and Earth System Science, 15(10), 2331-2346.
26. Song, D., Wang, X. H. (2013). Suspended sediment transport in the Deepwater Navi-gation Channel, Yangtze River Estuary, China, in the dry season 2009: 2. Numerical simulations. Journal of Geophysical Research: Oceans, 118(10), 5568-5590.
27. Song, D., Wang, X. H., Kiss, A. E., Bao, X. (2011). The contribution to tidal asym-metry by different combinations of tidal constituents. Journal of Geophysical Research: Oceans, 116(C12).
28. Suh, S. W., Lee, H. Y., Kim, H. J. (2014). Spatio-temporal variability of tidal asym-metry due to multiple coastal constructions along the west coast of Korea. Estuarine, Coastal and Shelf Science, 151, 336-346.
29. Van der Wegen, M.,and Roelvink, J. (2012). Reproduction of estuarine bathymetry by means of a process-based model: Western Scheldt case study, the Netherlands. Geo-morphology, 179, 152-167.
30. Wang, Z. B., Jeuken, M., Gerritsen, H., De Vriend, H., Kornman, B. (2002). Mor-phology and asymmetry of the vertical tide in the Westerschelde estuary. Continental Shelf Research, 22(17), 2599-2609.
31. Yu, X. Y., Zhang, W., Hoitink, A. J. F. (2020). Impact of river discharge seasonality change on tidal duration asymmetry in the Yangtze River Estuary. Scientific Reports, 10(1).
32. Zhang, E., Savenije, H., Chen, S., Mao, X. (2012). An analytical solution for tidal propagation in the Yangtze Estuary, China. Hydrology and Earth System Sciences, 16(9), 3327-3339.
33. Zhang, W., Cao, Y., Zhu, Y. L., Zheng, J. H., Ji, X. M., Xu, Y. W., Wu, Y., Hoitink, A. J. F. (2018). Unravelling the causes of tidal asymmetry in deltas. Journal of Hydrology, 564, 588-604.
34. Zhu, Z.-N., Zhu, X.-H., Guo, X. (2017). Coastal tomographic mapping of nonlinear tidal currents and residual currents. Continental Shelf Research, 143, 219-227.
35. 曾志明(2000)，「河口三角洲成長過程之研究」，國立成功大學水利及海洋工程學系博士論文。
36. 經濟部水利署第六河川局(2019)，「台南海岸防護(急水溪口至曾文溪口)基本資料監測調查分析」。
37. 經濟部水利署第六河川局(2019)，「曾文溪輸砂對鄰近海岸砂源補充監測」。
38. 臺南市政府(2019)，「臺南市鹿耳門溪口海岸監測調查及淤沙問題之研究評估」。