Dynamics of salt intrusion in the Mekong Delta; results of field observations and integrated coastal-inland modelling
Dynamics of salt intrusion in the Mekong Delta; results of field observations and integrated coastal-inland modelling
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DOI：
10.5194/esurf-2020-109
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发表时间：
2021-01
影响因子：
3.4
通讯作者：
Sepehr Eslami;P. Hoekstra;H. Kernkamp;Nam Nguyen Trung;Dung Do Duc;Hung Nguyen Nghia;Tho Tran Quang;Arthur van Dam;S. Darby;D. Parsons;G. Vasilopoulos;L. Braat;M. van der Vegt
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作者：
Sepehr Eslami;P. Hoekstra;H. Kernkamp;Nam Nguyen Trung;Dung Do Duc;Hung Nguyen Nghia;Tho Tran Quang;Arthur van Dam;S. Darby;D. Parsons;G. Vasilopoulos;L. Braat;M. van der Vegt
抽象的。在世界上最大的三角洲所面临的挑战清单中，盐分入侵的增加及其在危及淡水供应方面的作用往往排在非常靠前的位置。然而，详细的过程为基础的研究，在整个三角洲规模的盐入侵是有限的，并定期与全球海平面上升的趋势。在这里，使用现场测量和一个复杂的三维模型，集成了河流，农村，河口和沿海动态在一个数值域，我们研究盐入侵的湄公河三角洲的规模在广泛的细节。虽然许多研究将盐侵问题缩小到河口内的一个主题，但我们表明，大陆架是三角洲的内在组成部分，其物理过程，如季风驱动的海洋浪涌，直接影响三角洲内的盐度动态。大陆架上20-40厘米的浪涌的典型值有助于进一步的盐侵入达10公里。三角洲的河口系统也比许多其他系统更敏感的上游流量变化。此外，春小潮的变化在三角洲的盐入侵中起着关键作用。小潮和大潮之间的分层到混合系统的河口变化发展了三维过程，如河口环流和潮汐应变，成为主要的上游盐输运机制。盐度动态的3D性质，以及上游和下游过程的作用，表明妥协的尺寸或范围的数值域，可以限制在三角洲的盐入侵预测的准确性。该研究还表明，在过去的二十年中，河床切割响应人为沉积物饥饿，增加了分层，并激活或放大了三维盐运输子过程，放大上游盐运输。三角洲上的所有外力，即气候变化和上游大坝改变的水文状况，由于更深的河口通道（由采砂和上游蓄水驱动），三角洲本身更容易受到即使是温和的自然事件。这说明了保护沉积物平衡和河床水位对保护世界三角洲免受盐入侵的根本重要性。
Abstract. In the list of challenges facing the world largest deltas, increased salt intrusion and its role in jeopardizing freshwater supply is often ranked very high. Yet, detailed process-based studies of salt intrusion at the whole delta scale are limited and the trends are regularly associated to global sea level rise. Here, using field measurements and a sophisticated 3D model that integrates the riverine, rural, estuarine, and coastal dynamics within one numerical domain, we study salt intrusion at the scale of the Mekong Delta in extensive detail. While many studies down-scale the salt intrusion problem to a topic within an estuary, we show that the continental shelf is an intrinsic component of the delta, and its physical processes, such as monsoon-driven ocean surge, directly influence salinity dynamics within the delta. Typical values of 20–40 cm surge over the continental shelf contribute to up to 10 km of further salt intrusion. The delta's estuarine system is also more sensitive than many other systems to upstream discharge variations. Furthermore, spring-neap variability plays a key role in salt intrusion in the delta. The estuarine variability from a stratified to a mixed system between neap and spring tides develops 3D processes such as estuarine circulation and tidal straining that become the main upstream salt transport mechanisms. The 3D nature of salinity dynamics, and the role of upstream and downstream processes, suggests that compromising on dimension or extent of the numerical domain, can limit the accuracy of predictions of salt intrusion in the delta. The study also showcases that riverbed incision in response to anthropogenic sediment starvation in the last two decades, has increased stratification, and activated or magnified 3D salt transport sub-processes that amplify upstream salt transport. With all the external forces on the delta namely climate change and altered hydrological regime by the upstream dams, due to deeper estuarine channels (driven by sand mining and upstream impoundments), the delta itself is far more vulnerable to even mild natural events. This exemplifies the fundamental importance of preserving the sediment budget and riverbed levels in protecting the world's deltas against salt intrusion.