Climatic and Autogenic Controls on the Morphodynamics of Mega-Rivers: Modelling Sediment Flux in the Alluvial Transfer Zone

巨型河流形态动力学的气候和自生控制：冲积转移带沉积物通量建模

• 批准号: NE/J021571/1
• 负责人: Rolf Aalto
• 金额: $ 26.8万
• 依托单位: UNIVERSITY OF EXETER
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2012
• 资助国家: 英国
• 起止时间: 2012 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=NE%2FJ021571%2F1
• 关键词: Climatic; Autogenic; Controls; Morphodynamics; Mega

The world's largest rivers transport ~19 billion tonnes of sediment each year, with a significant fraction being sequestered in the large deltas that are home to 14% of the world's population. Most (>70%) of these large deltas are under threat from rising sea levels, ground surface subsidence & declining riverine sediment supply required for delta construction. However, while measurements & projections of sea level rise & subsidence exist for many deltas, data quantifying historic changes in fluvial sediment supply are sparse, limiting our understanding of how delta building is related to climatic fluctuations. This situation reflects the complexity of controls on river sediment loads, which include the influence of climate & land use change in upland areas, dam construction, & flood driven storage & remobilisation of sediment within the extensive floodplains that characterise the lowland reaches ("sediment transfer zones") of the world's major rivers. This project will provide the first comprehensive quantification of these controls on riverine sediment fluxes for one of the world's largest rivers (the Mekong), leading to new generic understanding of the relationships between climatic variability, fluvial processes & sediment flux to deltaic zones & the ocean.To meet this aim we will develop a new generic simulation model that will, for the very first time, quantify the effects of climatic & morphological controls on all individual components, & at sub-annual resolution, of the alluvial sediment transfer budget of a large river. The approach is to use a hydrological model to predict sediment supplied from the catchment to the head of the river's sediment transfer reach (the part of a river that links sediment source areas upstream with sediment sinks downstream). Within the transfer reach the model will account for the key morphodynamic processes of river bed & bank erosion, & floodplain sedimentation, which either supply material to the transfer reach, or store the material for later release. The model will be parameterised & validated using targeted field data that we will collect in this proposal. We will run the model to explore historical trends of within-reach sediment fluxes over a multi-decadal period encompassing the last 50+ yrs. The data derived from our simulation model will be unique: the very first annually resolved mega-river sediment budget encompassing a multi-decadal period. These data will enable us to explore a series of specific research questions: What is the net effect on the Mekong sediment load of sediment exchanges within the alluvial transfer reach? Do sediment fluxes associated with floodplain storage & bank erosion promote a net increase or reduction in efflux from the transfer zone? How large is this modulating effect in both absolute & relative terms? How strong is the interannual variability in this modulation, & what factors drive this? In fact, we expect interannual variability to reflect the net effect of changes in the various components of the budget linked to specific climate indices that control each component. This will be explored by testing specific hypotheses concerning (i) the role of specific modes of climate variability (Indian Ocean Dipole & the El-Niño Southern Oscillation) in modulating sediment transfer, and; (ii) the ways in which extreme events (associated with tropical cyclones) control river bank erosion & floodplain deposition. Predicting fluvial sediment transfer through one of the world's great rivers is a scientific challenge that is novel, timely & significant. Addressing this challenge will improve our ability to predict sediment transfer from 'source-to-sink' thereby aiding (i) interpretations of floodplain sedimentary records, (ii) understanding of how sediment, nutrient & carbon fluxes respond to climate, (iii) assessment of changes in flood risk within deltas, & (iv) the physical processes by which ecosystem services within large rivers are sustained.

世界上最大的河流每年输送约190亿吨沉积物，其中很大一部分沉积在占世界人口14%的大型三角洲。这些大型三角洲中的大多数（>70%）都受到海平面上升，地面沉降和三角洲建设所需的河流沉积物供应下降的威胁。然而，虽然许多三角洲存在海平面上升和沉降的测量和预测，但量化河流沉积物供应历史变化的数据很少，限制了我们对三角洲建设与气候波动之间关系的理解。这种情况反映了控制河流泥沙负荷的复杂性，包括气候和高地地区土地利用变化的影响、大坝建设、洪水驱动的沉积物储存和在覆盖世界主要河流的低地河段（“沉积物转移区”）的广阔洪泛区内的沉积物再流动。该项目将首次对世界上最大的河流之一的河流沉积物通量的这些控制进行全面的量化（湄公河），导致对气候变化，河流过程和沉积物通量到三角洲区和海洋之间的关系的新的一般理解。为了实现这一目标，我们将开发一个新的通用模拟模型，它将首次，量化气候和形态控制对所有单个组成部分的影响，并在次年度分辨率，一条大河的冲积泥沙转移预算。该方法是使用水文模型来预测从集水区到河流泥沙转移河段（连接上游泥沙源区和下游泥沙汇的河流部分）源头的泥沙供应。在转移河段内，模型将考虑河床和河岸侵蚀以及漫滩沉积的关键形态动力学过程，这些过程要么向转移河段提供材料，要么储存材料供以后释放。该模型将使用我们将在本提案中收集的目标现场数据进行参数化和验证。我们将运行该模型，以探索在过去50多年的几十年期内河段内泥沙通量的历史趋势。从我们的模拟模型中获得的数据将是独一无二的：第一个每年解决的大型河流泥沙预算涵盖了几十年期。这些数据将使我们能够探索一系列具体的研究问题：什么是湄公河泥沙负荷的冲积转移范围内的泥沙交换的净效应？与河漫滩蓄水和河岸侵蚀有关的泥沙通量是否促进了来自转移区的净流出量的增加或减少？这种调节作用的绝对值和相对值有多大？这种调制的年际变率有多强，是什么因素驱动的？事实上，我们预计年际变化反映了与控制每个组成部分的特定气候指数相关的预算各个组成部分变化的净效应。这将通过测试以下方面的具体假设来探讨：（一）气候变化的具体模式（印度洋偶极子和厄尔尼诺南方涛动）在调节沉积物转移方面的作用;（二）极端事件（与热带气旋有关）控制河岸侵蚀和洪泛区沉积的方式。预测通过世界上最大的河流之一的河流泥沙转移是一个科学挑战，是新颖的，及时的和重要的。应对这一挑战将提高我们预测沉积物从“源到汇”转移的能力，从而有助于（i）洪泛区沉积记录的解释，（ii）了解沉积物，营养素和碳通量如何响应气候，（iii）评估三角洲内洪水风险的变化，以及（iv）大型河流内生态系统服务的物理过程。

项目成果

River bank instability from unsustainable sand mining in the lower Mekong River

• DOI: 10.1038/s41893-019-0455-3
• 发表时间: 2020-01-13
• 期刊: NATURE SUSTAINABILITY
• 影响因子: 27.6
• 作者: Hackney, Christopher R.;Darby, Stephen E.;Houseago, Robert C.
• 通讯作者: Houseago, Robert C.

Source-to-sink research: economy of the Earth's surface and its strata

• DOI: 10.1016/j.earscirev.2015.11.010
• 发表时间: 2016-02
• 期刊: Earth-Science Reviews
• 影响因子: 12.1
• 作者: J. Walsh;P. Wiberg;R. Aalto;C. Nittrouer;S. Kuehl

Multiscale structure of meanders

• DOI: 10.1002/2016gl068238
• 发表时间: 2016-04
• 期刊: Geophysical Research Letters
• 影响因子: 5.2
• 作者: B. Vermeulen;A. Hoitink;G. Zolezzi;J. Abad;R. Aalto