Tracking sediment waves through Himalayan fluvial cascades following extreme mass flows

山区景观经历了突然而猛烈的地质灾害，如山体滑坡、湖泊暴发洪水和泥石流。由于气候变化，这类事件的规模和频率预计将增加，从而增加景观的不稳定性。这些景观也正在经历快速的人口增长，直接使人和资产暴露在地质灾害之下，但也使它们暴露在事件发生后显现的、通常被忽视和无法量化的遗留影响中。许多山地地质灾害的遗留影响是加强了河流中的粗泥沙输送。这是一个问题，因为泥沙作为“推移质”运移是河道调整的主要驱动力。这些调整影响到：1)洪水风险，通过改变河床高程；2)河岸基础设施的完整性，如水电，通过堵塞取水口和快速蓄水水库；以及3)河流生态，通过重组河道底质。因此，至关重要的是，必须对山区河流在极端扰动后泥沙运输制度演变的速度和方式产生严格的限制知识。然而，由于在不稳定的洪灾后地貌中工作的技术限制和挑战，我们对这类系统的行为几乎没有第一手信息，这一项目旨在解决这一问题。这一新项目将巩固来自英国和印度的领先研究人员的新国际合作伙伴关系。该团队由普利茅斯大学领导，与印度理工学院(IITR)、瓦迪亚喜马拉雅地质研究所(WIHG)、埃克塞特大学和纽卡斯尔大学密切合作。多样化的小组带来了地貌学、水文学和环境传感器网络方面的互补专业知识，如果没有国际合作伙伴的区域知识、技术能力和实地经验，这项工作是不可能的。该项目还包括职业生涯早期和中期的著名研究人员担任领导角色。我们将共同努力，应用一套创新的环境监测和建模工具来描述印度北阿肯德邦阿拉克南达河的水文和泥沙输送状况，该河流在2021年2月经历了一场极端的泥石流，通过试点工作证明，这场泥石流造成200人死亡，并引发了泥沙输送的增强。为了实现我们的目标，我们将：1)开发阿拉克南达河流域的新水文模型，使我们能够识别和区分水流的关键成分(如积雪融化和降雨)。这些信息将被用来更好地了解泥沙输送的水文驱动因素；2)利用无人机和卫星观测和模拟，量化河道沙洲的粒度特征。这些信息将使我们能够探索颗粒尺寸随时间的下游变化，并检查Chamoli事件的影响；3)部署创新的、低成本的“智能”标签，以跟踪作为泥沙移动的鹅卵石和巨石的运动。我们将利用低成本的被动地震对泥沙输送的时间和相对强度进行测量，以补充这些数据。我们将通过联合实地考察和IITR和WIHG的讨论，以及定期举行一系列虚拟项目会议和研讨会，面对面地进行技能和知识传授。我们将在同行评议的开放获取期刊上发表成果，并将编写一份技术总结报告，分发给当地利益攸关方。项目的成功将导致未来的联合筹资投标，这些投标将评估水电作为干扰山区河流粗泥沙输送的作用，并探索可减轻极端洪水的直接和遗留影响的业务做法。通过这样做，我们将进一步巩固涉及区域学者和从业人员的更广泛的研究网络，同时支持两国早期职业研究人员的发展。

Mountain landscapes experience sudden and violent geohazards, such as landslides, lake outburst floods, and debris flows. The size and frequency of such events is anticipated to increase due to climate change, enhancing landscape instability. These landscapes are also experiencing rapid population growth, directly exposing people and assets to geohazards, but also exposing them to legacy impacts which manifest after an event and are commonly overlooked and unquantified. A legacy impact of many mountain geohazards is enhanced coarse sediment transport in rivers. This is a problem because sediment travelling as 'bedload' is the primary driver of river channel adjustment. These adjustments affect: 1) flood hazard, by modifying channel bed elevation; 2) the integrity of riparian infrastructure, e.g. hydropower, by blocking intakes and rapidly filling reservoirs, and 3) fluvial ecology, by reorganising channel substrate. It is therefore vital to generate well-constrained knowledge of the pace and manner in which the bedload transport regime evolves in mountain rivers after extreme disturbances. However, due to technical limitations and challenges associated with working in unstable, post-flood landscapes, we have little first-hand information on the behaviour of such systems, which this project aims to address.This new project will consolidate a new international partnership of leading researchers from the UK and India. The team is led by the University of Plymouth, working in close collaboration with the Indian Institute of Technology Roorkee (IITR) and the Wadia Institute of Himalayan Geology (WIHG), the University of Exeter, and Newcastle University. The diverse team bring complementary expertise in geomorphology, hydrology, and environmental sensor networks, and the work would not be possible without the regional knowledge, technical competencies, and field experience of the international partners. The project also features prominent early- and early-to-mid-career researchers in leading roles. Working together we will apply a suite of innovative environmental monitoring and modelling tools to characterise the hydrological and bedload transport regime of the Alaknanda river, Uttarakhand, India, which experienced an extreme debris flow in February 2021 which killed >200 people and triggered enhanced sediment transport as a legacy impact, evidenced through pilot work.To achieve our aim, we will: 1) Develop a new hydrological model of the Alaknanda catchment, enabling us to identify and disentangle the key components of flow (e.g. snowmelt, rainfall). This information will be used to better understand the hydrological drivers of sediment transport; 2) Quantify the grain size characteristics of channel bars using drone- and satellite-based observations and modelling. This information will allow us to explore downstream transitions in grain size through time and examine the influence of the Chamoli event; 3) Deploy innovative, low-cost 'smart' tags to track the motion of cobbles and boulders travelling as bedload. We will supplement these data with measurements of the timing and relative magnitude of bedload transport using low-cost passive seismics. We will effect skills and knowledge transfer in-person via joint fieldwork and discussions at IITR and WIHG), and a regular series of virtual project meetings and seminars. We will publish results in peer-reviewed open-access journals and will produce a technical summary report which we will disseminate to local stakeholders. Project success will lead to future joint funding bids which will appraise the role of hydropower as a disruptor to coarse sediment transport in mountain rivers and explore operational practices that can mitigate the immediate and legacy impacts of extreme floods. In doing so we will further consolidate a wider research network involving regional academics and practitioners, whilst supporting the development of early career researchers in both countries.