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

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.