Deciphering the dominant drivers of contemporary relative sea-level change: Analysing sediment deposition and subsidence in a vulnerable mega-delta

解读当代相对海平面变化的主要驱动因素：分析脆弱巨型三角洲的沉积物沉积和沉降

• 批准号: NE/P008100/1
• 负责人: Stephen Darby
• 金额: $ 4.87万
• 依托单位: University of Southampton
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2017
• 资助国家: 英国
• 起止时间: 2017 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FP008100%2F1
• 关键词: Deciphering; dominant; drivers; contemporary; relative

The world's major river deltas are facing a major sustainability crisis. This is because they are under threat from being 'drowned' by rising sea levels, with potentially severe consequences for the 500 million people who live and work there. At a qualitative level we have a relatively well developed understanding of the processes that are driving these rising sea levels. Changes in delta surface elevation occur when the summed rates of eustatic sea level rise and ground-surface subsidence are not balanced by gains in surface elevation, the latter being caused by the deposition of sediments supplied from river catchments upstream. Ongoing and major environmental changes are seemingly driving greater imbalances in these factors: eustatic sea levels are rising as a consequence of anthropogenic climate change while ground-surface subsidence, which occurs naturally in deltas as a result of sediment compaction, is in many cases being significantly accelerated by groundwater and/or hydrocarbon extraction. As a result, the only factor that could potentially offset these losses in delta surface elevation is sediment deposition on the delta surface. Unfortunately, many deltas are also being starved of their supply of river sediments as a result of anthropogenic activities, such as sand mining and damming, in the feeder catchments upstream. Estimating precise values of eustatic sea-level rise, sediment supply rate, surface deposition and ground-surface subsidence, is a significant challenge. In the near term the most significant factors in this balance are sediment deposition and subsidence (in the longer term eustatic changes will become relatively more significant). However, a particular issue in estimating sediment supply is that previous studies have focused on the sediment loads at the apices of deltas, with an almost complete absence of reliable data within the delta distributary channel network downstream of the apex. Moreover, the diversity of relevant disciplinary expertise involved in determining the other drivers contributing to relative sea-level rise has thus far conspired to inhibit the integrated synthesis that is really necessary to tackle the problem systematically.The world's third largest delta, the Mekong is SE Asia's rice basket and home to 20 million people, but it is being exposed to environmental risks as a result of rapid economic development, most notably through upstream damming and anthropogenic subsidence. The Mekong is therefore not only representative of many of the issues facing the world's deltas, but reliable data are urgently needed to help inform the sustainable management plans required to provide a safe operating space for the delta's inhabitants. In our NERC funded work we have developed new methods to estimate recent historical and future trends in the river sediments supplied to the apex of the delta. However, it is the flows of sediment within delta distributary networks, downstream of the delta apices, that are most critical in controlling local rates of delta surface deposition. In this proposal we will collaborate with Can Tho University and the Vietnamese Hydrological agency to access archived sediment transport measurements. Using novel methods developed in our existing work in the catchment upstream we will 'unlock' and translate these data into the very first estimates of sediment loads within and across the delta distributary network itself. Meanwhile, we will also work with other international groups who have been developing novel models to simulate rates of delta surface deposition (Potsdam) and ground-surface subsidence (Utrecht). Working together we will draw these data together to build the first integrated assessment of the factors driving near-term relative sea-level rise in a globally significant, iconic, delta, providing a template for similar analyses in other vulnerable deltas worldwide.

世界主要河流三角洲正面临着重大的可持续性危机。这是因为他们正面临海平面上升的“淹没”威胁，这可能会对在那里生活和工作的5亿人造成严重后果。在定性层面上，我们对推动海平面上升的过程有了相对较好的了解。当海平面上升和地面沉降的总速率与地面高程的增加不平衡时，三角洲表面高程就会发生变化，后者是由上游河流集水区提供的沉积物沉积造成的。正在发生的重大环境变化似乎使这些因素更加不平衡：由于人为气候变化，海平面上升，而由于沉积物压实，三角洲自然发生的地面沉降在许多情况下由于地下水和/或碳氢化合物的开采而大大加速。因此，可能抵消三角洲表面高程损失的唯一因素是三角洲表面的沉积物沉积。不幸的是，许多三角洲由于人为活动，如在上游的补给集水区采沙和筑坝，也缺乏河流沉积物的供应。估计海平面上升、沉积物供应率、地表沉积和地面沉降的精确值是一项重大挑战。在近期内，这种平衡中最重要的因素是沉积物沉积和沉降（在较长期内，海平面变化将变得相对更重要）。然而，在估计沉积物供应的一个特殊问题是，以前的研究都集中在三角洲的顶点的泥沙负荷，几乎完全没有可靠的数据内的三角洲分流河道网络下游的顶点。此外，在确定导致相对海平面上升的其他驱动因素方面，相关学科的专业知识多种多样，迄今为止，这些知识共同阻碍了系统地解决这一问题所真正需要的综合性综合。世界第三大三角洲湄公河是东南亚的米篮子，也是2000万人口的家园，但由于经济的快速发展，特别是上游筑坝和人为沉降，它正面临环境风险。因此，湄公河不仅代表了世界三角洲面临的许多问题，而且迫切需要可靠的数据来帮助制定可持续管理计划，为三角洲居民提供安全的操作空间。在我们NERC资助的工作中，我们开发了新的方法来估计三角洲顶点河流沉积物的近期历史和未来趋势。然而，在三角洲顶部下游的三角洲分流网络内的沉积物流动，是控制三角洲表面沉积的局部速率的最关键因素。在本提案中，我们将与坎托大学和越南水文局合作，以获取存档的泥沙输运测量数据。使用我们在上游集水区现有工作中开发的新方法，我们将“解锁”并将这些数据转化为三角洲分流网络内部和整个三角洲分流网络本身的泥沙负荷的第一次估计。与此同时，我们还将与开发新模型的其他国际小组合作，模拟三角洲表面沉积（波茨坦）和地面沉降（乌得勒支）的速度。通过共同努力，我们将把这些数据汇集在一起，对全球重要的标志性三角洲近期相对海平面上升的驱动因素进行首次综合评估，为全球其他脆弱三角洲的类似分析提供模板。