High resolution mapping of fine sediment and pollutants throughout large river cross sections with innovative uncrewed survey boats; supporting improv

除了14%的英国河流外，所有河流都不符合环境署对良好生态状态的定义，没有一条河流被评为化学状态良好1。因此，细粒沉积物(沙粒和细粒)和其他污染物通过河流系统的数量和传输仍然是研究人员和流域利益攸关方主要感兴趣的问题，因为这对于了解和量化污染物和养分转移的过程具有基本的重要性。沉积物的迁移和沉积是河流地貌和由此形成的生境的关键，而生境又决定着生物多样性。此外，泥沙通量的知识对于确定基础设施的可持续性(水电、防洪)、洪水风险、农业土壤流失和沐浴水安全非常重要。然而，在大断面和/或复杂和动态的河流中，通量在断面上会有很大的变化。虽然细颗粒通常被认为是相对均匀地分布在整个流动横截面上，但这些颗粒的聚集可能意味着泥沙浓度可能会发生显着变化。鉴于这些变化难以量化、了解甚少，而且在估算沉积物和污染物通量方面可能很重要，这是一个优先研究领域。该项目的目的是首次解决这些细微沉积物和污染物运移的横断面差异，使泥沙预算估算、生境适宜性评估和洪水风险的影响能够逐步改变。拟议的项目重点是使用新的仪器以前所未有的分辨率解决沉积物和其他污染物的通量。首先，将使用先进的无人值守测量船在同一地点同时测量河流水力、悬浮泥沙和污染物。其次，将对观测到的变化进行调查，以阐明泥沙/污染物迁移及其控制的横断面变化。知识将通过在各种集水区设置和各种水流条件下进行观测而获得。将使用最先进的ADCP(声学多普勒水流剖面仪)仪器和多参数水质传感器进行径流、河流水力、细微沉积物和其他污染物的测量。这些仪器将使用配备有全球定位系统的无线电控制船只(ARCbove和ArCboatlite)进行远程部署，以便安全地调查大型且往往无法进入的河流和洪泛平原的水流(见图)。ADCP背向散射数据将根据现场物理水样(颗粒大小和质量)和独立的直接测量(浊度和颗粒大小)进行评估，以提供可靠的校准。这一复杂的校准程序特别适用于研究项目，并将有助于提供优化的技术方案。多频ADCP传感器应能对沉积物颗粒大小及其空间分布提供新的见解，而高分辨率的河流水力学数据将有助于说明沉积物被动员和沉积的环境、过程和条件。在一系列地点和时间与无人值守的船只进行的测量将有助于了解在一系列水流条件下影响水质的空间和时间因素。这将提供对下游通量的更准确的量化，使人们能够更好地了解控制沉积物和其他污染物迁移的因素和过程，从而控制化学、生物和生态状况以及沐浴水安全。

All but 14% of UK rivers fail to meet the Environment Agency definition of Good Ecological Status, and none are rated good for Chemical Status1. Therefore the amount and transportation of fine sediment (sand particles and finer) and other pollutants through river systems remains of major interest to researchers and catchment stakeholders because of the fundamental importance for the process-understanding and quantification of contaminant and nutrient transfer. Sediment transport and deposition is a key to in-stream geomorphology and the resultant habitat which in turn determines biodiversity. Furthermore, knowledge of sediment fluxes is important in determining infrastructure sustainability (hydropower, flood defences), flood risk, agricultural soil loss and bathing water safety.Traditionally, the most robust fine sediment flux estimates and pollutant measurements have been from continuous bank-side monitoring or spot sampling. However, in rivers with large cross sections and/or complex and dynamic hydromorphology, fluxes will vary greatly over cross sections. Although fine particles are often assumed to be relatively evenly distributed throughout flowing cross sections the aggregation of these particles can mean that significant variations in sediment concentration can occur. Given that these variations are challenging to quantify, poorly understood and are likely to be important in the estimation of sediment and pollutant fluxes this represents a priority research area. The aim of this project is to resolve, for the first time, these cross-sectional variations in fine sediment and pollutants transport, to enable a step-change in sediment budget estimation, habitat suitability assessment, and implications for flood risk.The proposed project focusses on the use of novel instrumentation to resolve sediment and other pollutant fluxes at previously unprecedented resolution. Firstly, simultaneous, co-located measurements of river hydraulics, suspended sediment and pollutants will be obtained using advanced uncrewed survey boats. Secondly, observed variations will be investigated to elucidate cross-sectional changes in sediment/pollutants transport and their controls. Knowledge will be gained by making observations in a variety of catchment settings and across a range of flow conditions. A state of the art ADCP (Acoustic Doppler Current Profiler) instrument and multi-parameter water quality sensors will be used to make streamflow, river hydraulics, fine sediment and other pollutants measurements. The instruments will be deployed remotely using Differential GPS equipped, radio-controlled boats (ARCboat and ARCboatlite) to allow the safe survey of large and often inaccessible river and floodplain flows (see photo). The ADCP backscatter data will be evaluated against in situ physical water samples (particle size and mass) and independent direct measurements (turbidity and particle size) to provide robust calibration. This sophisticated calibration procedure is particularly well suited to a research project and will contribute to the delivery of an optimised techniques protocol. The multi-frequency ADCP sensor should allow new insights into sediment particle sizes and their spatial distribution, while the high-resolution river hydraulics data will help illustrate the settings, processes and conditions in which sediments are mobilised and deposited.Measurements undertaken with the uncrewed boats at a range of locations and times will help inform understanding of the spatial and temporal factors influencing water quality across a range of flow conditions. This will provide a more accurate quantification of downstream fluxes, enabling improved understanding of the factors and processes that control sediment and other contaminant transport, and hence chemical, biological and ecological status and bathing water safety.