Simulation of freshwater transport network and salt flux in the Bangladesh delta
Simulation of freshwater transport network and salt flux in the Bangladesh delta
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DOI：
10.1016/j.ecss.2022.107839
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发表时间：
2022-04
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通讯作者：
Yujuan Sun;L. Bricheno;M. Payo-Payo-M.-Payo-Payo-1403836608;Md. Munsur Rahman;N. M. Burns
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作者：
Yujuan Sun;L. Bricheno;M. Payo-Payo-M.-Payo-Payo-1403836608;Md. Munsur Rahman;N. M. Burns
由于恒河-雅鲁藏布江-梅克纳河三角洲易受气候变化的威胁，咸水循环对于保持该三角洲的水质十分重要。我们应用数值模型来研究孟加拉国GBM三角洲内的体积和盐的运输。为了了解潮汐和潮下（剩余）运输驱动的盐水入侵的组成部分，我们选择了19个横截面来代表复杂的三角洲环流在一个简化的网络模型。研究结果表明，丰水期GBM河82.51%以上的水量通过东部河口系统（EES）排泄，枯水期增加到98.37%。在湿季，剩余输运的大小可与潮汐输运相媲美，而在干季则小一个数量级。西部河口系统（WES）的经验，在旱季严重的盐度入侵，和强大的季节性变化，在潮汐和潮下输运，与抑制潮汐驱动的运输在雨季观察。我们的研究结果表明，下梅克纳河的子通道区域也面临着盐度入侵问题的风险，因为在旱季估计有更强的潮汐盐通量。潮量输移具有季节性，与河流流量的变化相对应。采用多项式展开的简化解来描述河道内的潮汐传播。潮汐能的内陆渗透率随着大的河流流量而减少，另外，潮波的传播速度在雨季增加。我们的分析有助于了解三个河口系统的季节性和潮汐控制的响应，并可用于通知河流管理的上游-下游的联系。
Circulation of saline water is important for maintaining water quality in the Ganges-Brahmaputra-Meghna (GBM) delta because of its vulnerability to the threat of climate change. We applied a numerical model to examine the volume and salt transports within the GBM delta, Bangladesh. To understand the components of salt water intrusion driven by tidal and subtidal (residual) transports, we selected 19 cross-sections to represent the complex delta circulation in a simplified network model. Our results show that over 82.51% of GBM river water drains through the eastern estuarine system (EES) in the wet season, increasing to 98.37% in the dry season. Residual transport can be comparable in size with the tidal transport in the wet season, and one order of magnitude smaller in the dry season. The western estuarine system (WES) experiences serious salinity intrusion in the dry season, and strong seasonal variability in both tidal and subtidal transport, with suppression of tide-driven transport observed during the wet season. Our results show the sub-channels area of the Lower Meghna River also faces the risk from salinity intrusion issues, as stronger tidal salt flux is estimated in the dry season. Tidal volume transport varies seasonally, corresponding to the variability of river discharge. A simplified solution by means of polynomial expansion was applied to describe the tidal propagation within river channels. Inland penetration of tidal energy is reduced with large river discharge, and additionally the propagation speed of the tidal wave increases in the wet season. Our analysis helps understand the response of the three estuarine systems to seasonal and tidal controls, and can be used to inform river management about the upstream-downstream linkages.