Massimo Guerrero

Rivers transport a variety of materials, among which, recently, plastics. The transport of plastic fragments and small pieces, referred to as microplastics (MPs), has borrowed methods and approaches from sediment transport, with due adaptations. Past studies showed that the higher variability of densities and shapes encountered in plastics can be addressed within the classical sediment transport framework, but questions remain about how to fit plastic into such framework. Sediment and plastic transport in rivers requires both the understanding of the plastic-specific transport behaviour per se , and an expansion of definitions and methodology to fit the new needs imposed by plastic presence. Here we propose a method to define the onset of transport depending on the availability of mobile material, and apply it to the case of sparse MPs on natural beds. Laboratory experiments on homogeneous (corresponding to MPs’ total bed cover) and mixed (corresponding to much reduced MPs bed cover spanning 0.05–1%) bed experiments are presented and discussed, allowing a better understanding of the onset of transport process in the case of a bed composed of different material fractions. The role of bed sediments and their induced hydrodynamics aligns with literature results, with the exception of the lightest MPs we tested, which moved on a sandy bed at conditions one order of magnitude lower than previously observed. When looking at the role of availability, we observed that the higher the availability, the lowest the bed shear stresses needed to start transport. Average values disregarding the availability variations show good agreement with published literature. The effects of availability are here investigated for the first time, and shed light on the potential underestimation of MPs fluxes by present models.

Rivers are subject to increasing human pressure, resulting in a loss of their natural characteristics, further enhanced by climate change. The present study focuses on a piedmont reach of the Italian Po River and combines Landsat satellite information with hydrological records to investigate changes in sandbars exposure and riparian vegetation coverage, considering the summer period of 1984–2022. Satellite data were handled via Google Earth Engine, looking at common indexes such as the Modified Normalized Difference Water Index, which was used to identify temporal variations in wetted channel area, and the Normalized Difference Vegetation Index, considered as a proxy of vegetation coverage variations. Changes in the river hydrology were analysed by looking at the annual minimum water levels, the discharge duration curve, the stage–discharge relationship and the yearly annual water volume. Results suggest that a process of oversimplification is affecting this reach of the Po River, showing how climate change can affect piedmont European watercourses. Indeed, after an initial period where bars tended to be barer and somehow stable over time, in the most recent decade a different trend appeared, with vegetation able to colonize the exposed sandbars more. Using the Po River as an exemplary case study, this work suggests that prolonged dry periods, which are more common in recent decades, might impact large and medium rivers located in temperate climates, favouring the development of vegetation on exposed sandbars, eventually resulting in a less dynamic active channel.

The Cheves hydroelectric power plant (HPP) is located in the Andes Mountains in Peru near Lima. The operation of the Statkraft asset is heavily influenced by sediment transport during the rainy season (February to June), both by bed load and suspended load. To avoid sediments from filling up the reservoir, sediment routing during rainy season is applied. However, during the routing, high water velocities through the gates are causing flab abrasion resulting in high maintenance costs. In addition, the water being transferred to the head race tunnel is of high sediment concentration and causes severe erosion of the turbine blades, resulting in low efficiency. This occurs despite desanders are operating continuously during rainy season.To optimize the operation of the power plant, both during power production and during sediment routing, a sediment monitoring instrument was installed at four locations on the HP system. The positions were chosen to provide accurate information on sediment inflow to all major units of HP, such as the desilting units, reservoir, forebay, headrace tunnel, and turbine outlets. Both acoustic (e.g., 8 MHz, acoustic backscatter) and optical (e.g., optical backscatter) instruments will be installed to accurately estimate suspended sediment concentration (SSC). The AoBS, manufactured by Sequoia AS, provides both acoustic-optical measurements and a proprietary method for combining the measurements and determining the SSC in mg/l. To validate SSC, a pump sampler was installed at each location to sample once a day in dry season and twice a day in the wet season. The water samples were analyzed using both the typical filter method and the laser diffraction method.The initial results (in the dry season) confirmed that the combination of optical and acoustic methods provided the most accurate results, although the Sequoia AS method appears to underestimate by 30-50%. Another method based on a weighted summation of both results is under development and promises better results for the existing data. Based on these results, four indicators have been developed: i) intensity of sediment inflow in the turbine, ii) coarseness of particles at all positions (optics vs acoustics scattering index), iii) sediment discharge, iv) desander performance (sediment input from the desanders). Further testing needs to be conducted in the wet season to validate the indicators as well as the method of combined acoustic-optical sediment data collection.

W.A.T.E.R. stands for Workshop on Advanced measurement Techniques and Experimental Research. It is an initiative started in 2016 in association with the Experimental Methods and Instrumentation (EMI) committee of the International Association for Hydro-Environment Engineering and Research (IAHR) aimed at advancing the use of experimental techniques in hydraulics and fluid mechanics research. It provides a structured approach for the learning and training workshop series to postgraduate students (aiming specifically at doctoral students), young researchers, and professionals with an experimental background in fluid mechanics. It offers an opportunity to learn about state-of-the-art instrumentation and measurement techniques and the latest developments in the field by partnering with manufacturers. W.A.T.E.R. brings together academics, instrumentation manufacturers and public sectors in a structured setting to share knowledge and to learn from good practices. It is about training people who already have a certain knowledge and skill level but who need to go deeper and/or wider in the field of measurement and experimental research.

Bedload transport is an important factor to describe the hydromorphological processes of fluvial systems. However, conventional bedload sampling methods have large uncertainty, making it harder to understand this notoriously complex phenomenon. In this study, a novel, image-based approach, the Video-based Bedload Tracker (VBT), is implemented to quantify gravel bedload transport by combining two different techniques: Statistical Background Model and Large-Scale Particle Image Velocimetry. For testing purposes, we use underwater videos, captured in a laboratory flume, with future field adaptation as an overall goal. VBT offers a full statistics of the individual velocity and grainsize data for the moving particles. The paper introduces the testing of the method which requires minimal preprocessing (a simple and quick 2D Gaussian filter) to retrieve and calculate bedload transport rate. A detailed sensitivity analysis is also carried out to introduce the parameters of the method, during which it was found that by simply relying on literature and the visual evaluation of the resulting segmented videos, it is simple to set them to the correct values. Practical aspects of the applicability of VBT in the field are also discussed and a statistical filter, accounting for the suspended sediment and air bubbles, is provided.

This contribution presents the effectiveness and the potentialities of a consolidated technique—the video-cluster analysis—to the study of turbulent flow and breaking waves, in order to demonstrate its suitability as a low-cost, non-intrusive method to derive quantitative key parameters describing the wave–structure interaction processes at coastal defense structures. For this purpose, a new methodology, consisting of a series of pre- and post-processing techniques developed to optimize the automatic detection of clusters in video imagery, was designed to process the video-records of experiments of wave run-up and wave overtopping at sea-dikes subjected to irregular waves. The results of the cluster analysis were elaborated to reconstruct the instantaneous profiles of the free-surface elevations across the structure crest and derive simultaneous information on overtopping volumes, discharges, depths, and velocities and to get spatial-time maps of the concentration of the air entrapped in the liquid phase. The accuracy of the methodology is demonstrated by comparing the quantities derived from the cluster analysis to laboratory measurements performed with resistive gauges and acoustic Doppler profilers. The novelty of the work is either represented by the results of the application of the cluster-analysis and by the procedures of optimizations, whose ensemble may establish a best practice and represent a guideline for other applications.

With the increasing availability of big geospatial data (e.g., multi-spectral satellite imagery) and access to platforms that support multi-temporal analyses (e.g., cloud-based computing, Geographical Information Systems, GIS), the use of remotely sensed information for monitoring riverine hydro-morpho-biodynamics is growing. Opportunities to map, quantify and detect changes in the wider riverscape (i.e., water, sediment and vegetation) at an unprecedented spatiotemporal resolution can support flood risk and river management applications. Focusing on a reach of the Po River (Italy), satellite imagery from Landsat 5, 7, and 8 for the period 1988–2018 were analyzed in Google Earth Engine (GEE) to investigate changes in river planform morphology and vegetation dynamics associated with transient hydrology. An improved understanding of these correlations can help in managing sediment transport and riparian vegetation to reduce flood risk, where biogeomorphic processes are commonly overlooked in flood risk mapping. In the study, two established indices were analyzed: the Modified Normalized Difference Water Index (MNDWI) for monitoring changes in the wetted river planform morphology, inferring information about sediment dynamics, and the Normalized Difference Vegetation Index (NDVI) for evaluating changes in vegetation coverage. Results suggest that planform changes are highly localized with most parts of the reach remaining stable. Using the wetted channel occurrence as a measure of planform stability, almost two-thirds of the wetted channel extent (total area = 86.4 km²) had an occurrence frequency >90% (indicating stability). A loss of planform complexity coincided with the position of former secondary channels, or zones where the active river channel had narrowed. Time series analysis of vegetation dynamics showed that NDVI maxima were recorded in May/June and coincided with the first peak in the hydrological regime (occurring in late spring and associated with snowmelt). Seasonal variation in vegetation coverage is potentially important for local hydrodynamics, influencing flood risk. We suggest that remotely sensed information can provide river scientists with new insights to support the management of highly anthropized watercourses.

Both the apparent bedload velocity and the backscattering strength measured by acoustic Doppler current profilers could assist bedload assessment in the field. To test this hypothesis, two ADCPs working at three frequencies (3 MHz and 1 MHz, M9; 2 MHz, StreamPro) were deployed simultaneously to measure seven different bedload transport conditions in a laboratory flume. The bedload transport was monitored by two high-speed cameras and a bedload trap. For some experiments 3 MHz and 1 MHz delivered spatially averaged apparent velocity, for others the velocity corresponded to the average velocity of particles. The 2 MHz severely underestimated the average particle velocity. The M9 backscattering strength decreased as the bedload concentration increased, independently of the size and velocity of transported particles. The 2 MHz resulted in almost constant backscattering strength. These findings demonstrate that further examination of the acoustic configurations and parameters could lead to a methodology for bedload quantification based solely on the acoustic outputs.