The sedimentology of fluvial megascours

河流的一个共同特征是，在弯道或两条河道交汇的地方，它们冲刷河床的深度远远超过沿途的平均深度。在世界上最大的河流中，这类特征确实是深达50米的“巨型河流”。然而，尽管它们普遍存在，但由于从这些位置获得测量数据的相关问题，它们是一个相对未量化的现象。这种缺乏理解很重要，因为对大都市的了解具有许多关键的社会应用(破坏基础设施)和经济应用(碳氢化合物勘探)。为了解决这一紧迫问题，该提案提出了一种独特的方法，其基础是应用最先进的高分辨率海洋地震技术，以及取心和数值模拟方案，这将使与大型场地有关的长期争议得以解决。这项提议将世界上最大的河流之一孟加拉国贾穆纳河的海洋科学家、河流沉积学家和数值建模人员之间的一项新合作结合在一起。海洋地震系统被广泛用于在近海环境中提供高分辨率的地下图像，但从未在河流中应用过。然而，通过利用南安普敦国家海洋学中心开发的新技术，我们的团队现在能够生成第一个河流巨流形态和相关沉积物的定量数据集。我们的重点将是恒河和贾穆纳河汇合处附近以及更远的下游地点的冲刷。在这些地点，将通过收集地震反射数据(通过取心计划和一些额外的探地雷达数据)来了解河床下的情况，而作用于河床的性质和过程将根据多波束回声测深仪数据确定。这将使冲刷的形态和相关的填方得以量化，并使地点之间的任何下游变化得到充分评估。我们将使用这些数据来评估一个巨流沉积学的数值模型，然后可以第一次使用该模型来测试对比的概念模型，这些模型主要是在缺乏数据的情况下推断出的，即巨流如何运行以及它们在岩石记录中的样子。因此，该项目的一个关键成果将是第一个经过充分评估的冲刷带地层学通用数值模型，该模型将广泛适用于大范围的大河流。我们还将制定在河流内进行地震勘探的协议，从而为其他国家开放技术。这有可能对这一学科产生变革性的影响，允许收集新的数据集，从而促进基础河流科学的进步。我们的工作揭示的一般性理解也将有一些重要的应用，将作为我们影响路径的一部分进行探索。因此，我们将通知政策制定者和当地社区，并与碳氢化合物行业的专家合作。

A common feature of rivers is that at bends, or where two channels join, they scour out their beds to depths that greatly exceed the average depth along their course. In the World's largest rivers such features are truly 'megascours' reaching depths of 50 m. However, despite their widespread occurrence, they are a relatively unquantified phenomenon due to issues associated with obtaining measurements from such locations. This lack of understanding matters because knowledge of megascours has a number of key societal (destruction of infrastructure) and economic (hydrocarbon exploration) applications. To tackle this pressing issue this proposal presents a unique methodology based on application of state-of-the-art high resolution marine seismic technologies together with a programme of coring and numerical modelling that will allow long-standing controversies relating to megascours to be resolved. The proposal brings together a novel collaboration between marine scientists, river sedimentologist and numerical modellers in one of the World's largest rivers, the Jamuna, Bangladesh. Marine seismic systems have been used extensively to provide high resolution images of the subsurface in offshore environments but have never been applied in a river. However, by taking advantage of new technologies developed at the National Oceanography Centre, Southampton our team is now in a position to generate the first quantitative datasets of river megascour morphology and associated deposits. Our focus will be scours near the confluence of the Ganges and Jamuna rivers and at sites further downstream. Over these sites an understanding of the sub-riverbed will be achieved by the collection of seismic reflection data (informed by a programme of coring and some additional ground penetrating radar data), while the nature and processes acting on the riverbed will be determined from multi-beam echosounder data. This will allow morphology and the associated fill of scours to be quantified and any downstream changes between sites to be fully assessed. We will use this data to evaluate a numerical model of megascour sedimentology that can then be used, for the first time, to test contrasting conceptual models, largely developed on inference in the absence of data, of how megascours function and what they look like in the rock record. A key output of the project will thus be the first fully evaluated generic numerical model of scour zone stratigraphy that will be widely applicable to a broad range of large rivers. We will also have developed protocols for undertaking seismic surveys within rivers, so opening up the technology for others. This has the potential to have a transformative impact upon the discipline allowing new datasets to be collected that will allow advances in fundamental river science.The generic understanding revealed by our work will also have a number of important applications that will be explored as part of our Pathways to Impact. Thus we will inform policy-makers and local communities and collaborate with specialists in the hydrocarbon industry.