Geomorphic and sedimentary evolution of an extreme event: testing a sediment-based palaeoflood record

该项目将利用2015年12月坎布里亚郡的极端洪水，通过量化初始沉积事件、成岩演化和富含沉积物的洪水后集水区的影响，严格测试我们独特的、长（bbb600年）湖泊沉积记录的洪水强度和频率的完整性和响应性。最近的洪水，继2005年和2009年的极端洪水事件之后，突出了利用记录的河流流量（30-50年）开发的洪水强度/返回频率模型的不足之处，这些模型太短，无法满足准确测量洪水风险的社会要求，也无法解决有关气候强迫在最近事件中的作用的问题。我们在利物浦和达勒姆大学的研究团队开发的湖泊沉积档案为解决这一研究差距提供了必要的记录长度。这包括在Bassenthwaite的沉积物强度（事件粒度）特征，该特征与河流流量（40年）有很好的相关性，并确定过去十年发生了600年来最大的3次洪水。我们有三个具体目标：1。建立不同持水时间（21 ~ 350天）湖泊的深水沉积事件特征，并在湖泊有机生产力高峰夏季进行重复采样，以检验该事件和最近（2009年11月）的高震级事件在古洪水记录中的演变。建立和监测集水湖和湖内过程的洪水后调节如何改变或增强2015年事件的湖泊沉积物洪水信号。通过将最近的极端事件置于更长期的背景下，提高我们对现有古洪水系列的信心，并利用综合沉积物和河流流量数据建立洪水频率模型。该项目将利用对比洪水前后沉积记录和通量所提供的独特机会，建立英格兰西北部最极端洪水之一的沉积特征；至关重要的是，我们的湖泊沉积物记录被用作真实的洪水系列，从而有助于呼吁加强洪水记录，以准确定义这些以及潜在的更广泛的英国和世界河流系统的洪水风险。我们的团队在Brotherswater和Buttermere有现有的沉积物陷阱，在洪水（2012-2015）之前，在Eden集水区（Brotherswater和Ullswater (Glenridding)）和Cocker-Derwent集水区（Bassenthwaite和Buttermere）受到最近事件影响的关键地点采集了湖泊沉积物表面重力岩心。我们的研究方法旨在描述洪水沉积物的沉积信号（粒度、地球化学、质量累积），并每隔6周重复采样一次，以确定事件进入古记录的进程。我们还将监测洪水后湖泊的沉积物动态（每月沉积物捕获和连续浊度监测）和集水区，通过沉积物级联到湖泊（源到汇）的关键节点，量化集水区斜坡的沉积物供应（每周6次无人机无人机调查）。这将使我们能够将2015年12月洪水的沉积特征（粒度、地球化学）与更长的古洪水记录中的事件进行对比，并将这些数据结合到我们使用沉积物和河流流量记录的新型洪水频率模型中。这提供了一个无与伦比的机会，可以直接调查各种湖泊环境中最近的洪水沉积。独特的是，我们有机会对比洪水前和洪水后的沉积记录，并将我们正在开发的洪水强度和频率的长期数据放在一个坚实的基础上，这将使我们能够在利益相关者研讨会上鼓励国家组织、水文学家和工程师在洪水风险管理中充满信心地使用这些记录。

This project will use the December 2015 extreme flooding in Cumbria to critically test the integrity and responsiveness of our unique, long (>600 year) lake sedimentary records of flood magnitude and frequency by quantifying the initial sedimentary event, its' diagenetic evolution and the impacts of a sediment-rich post-flood catchment. The recent flooding, following previous extreme flood events in 2005 and 2009, has highlighted the inadequacies of flood magnitude / return-frequency models developed using recorded river flows (30-50 year), which are too short to address societal requirements for accurate measures of flood risk and to address questions regarding the role of climate forcing of recent events. Lake sedimentary archives developed by our research teams at Liverpool and Durham Universities provide the length of record necessary to address this research gap. This includes a sediment magnitude (event particle size) signature at Bassenthwaite that correlates well with river discharges (for 40 years) and identifies that the largest 3 floods in 600 years have occurred in the past decade. We have three specific aims:1. To establish the deep water sedimentary event signature for lakes with differing water retention times (21-350 days) and to use repeat sampling into the summer period of peak organic productivity in the lake to test the evolution of this and high magnitude events in the recent past (11/2009) into the palaeoflood record.2. To establish and monitor how post-flood conditioning of catchment-to-lake and within-lake processes modifies or augments the lake sediment flood signal for 2015 event.3. To improve confidence in our existing palaeoflood series by placing this recent extreme event in that longer term context, and to establish flood frequency models that use integrated sediment and river flow data.The proposed project will use the unique opportunity afforded by contrasting pre- and post-flood sedimentary records and fluxes to establish the sedimentary signature of one of NW England's most extreme floods; crucially to engender confidence in the use of our lake sediment records as genuine flood series, thus contributing to calls for enhanced flood records to accurately define flood risk in these and potentially wider UK and world river systems. Our team has existing sediment traps at Brotherswater and Buttermere, together with lake sediment surface gravity cores sampled before the flood (2012-2015) at key sites impacted by the recent events in the Eden catchment (Brotherswater and Ullswater (Glenridding)) and Cocker-Derwent catchment (Bassenthwaite and Buttermere). Our research methodology is designed to characterise the sediment signal (grain size, geochemistry, mass accumulation) of the flood deposits and repeat this sampling at 6 week intervals to establish the progression of the event into the palaeo-record. We will also monitor the post-flood sediment dynamics in the lake (monthly sediment trapping and continuous turbidity monitoring) and the catchment to quantify the supply of sediments from catchment slopes (6 weekly UAV drone surveys) through key nodes in the sediment cascade to the lake (source-to-sink). This will enable us to contrast the sedimentary characteristics (grain size, geochemistry) of the December 2015 flood with events in the longer palaeoflood record, and incorporate these data in our novel flood frequency modelling using combined sediment and river flow records.This provides an unparalleled opportunity to investigate directly recent flood sedimentation across a variety of lake environments. Uniquely, we have the opportunity to contrast the pre- and post-flood sedimentary records and place our developing long-term data on both flood magnitude and frequency on a robust footing, which will allow us at our stakeholder workshop to encourage national organisations, hydrologists and engineers to use these records with confidence in flood risk management.