Extreme, short-duration fluctuations caused by storage hydropower plant discharges or ‘hydropeaking’ occur when hydropower is used to cover the peak electrical loading conditions of a power network. The overall effects of hydropeaking can result in serious disturbances to the hydrologic regime, river morphology and the ecological condition of a river. In this study a transient, fuzzy logic based two-dimensional fish habitat model was used to investigate the stranding risk to juvenile European grayling (Thymallus thymallus) corresponding to different river morphologies. The stranding risk was simulated using two 24 hour discharge hydrographs in two alpine gravel bed river reaches. Both reaches were in close proximity to the hydropower plant outlet and were chosen due to their starkly contrasting morphological features. Spatially distributed stranding risk was determined based on a multi-step procedure which took into account the stationary habitat suitability, critical dewatering rates and flow depths. Although the number of reaches used in the investigation was limited in scope, clear distinctions with respect to the stranding risk were found. The reach with wider, flatter cross sections had a larger amount of stranding risk areas as compared to the reach with a steeply incised channel form. Stranding risk was found to be related to a specific set of changes in the discharge than to a particular rate of change or magnitude of the flow fluctuations. The temporal distribution of stranding risk was found to be almost identical for both reaches.

Hydropower globally represents the main source of renewable energy, and provides several benefits, e.g., water storage and flexibility; on the other hand, it may cause significant impacts on the environment. Hence sustainable hydropower needs to achieve a balance between electricity generation, impacts on ecosystems and benefits on society, supporting the achievement of the Green Deal targets. The implementation of digital, information, communication and control (DICC) technologies is emerging as an effective strategy to support such a trade-off, especially in the European Union (EU), fostering both the green and the digital transitions. In this study, we show how DICC can foster the environmental integration of hydropower into the Earth spheres, with focus on the hydrosphere (e.g., on water quality and quantity, hydropeaking mitigation, environmental flow control), biosphere (e.g., improvement of riparian vegetation, fish habitat and migration), atmosphere (reduction of methane emissions and evaporation from reservoirs), lithosphere (better sediment management, reduction of seepages), and on the anthroposphere (e.g., reduction of pollution associated to combined sewer overflows, chemicals, plastics and microplastics). With reference to the abovementioned Earth spheres, the main DICC applications, case studies, challenges, Technology Readiness Level (TRL), benefits and limitations, and transversal benefits for energy generation and predictive Operation and Maintenance (O&M), are discussed. The priorities for the European Union are highlighted. Although the paper focuses primarly on hydropower, analogous considerations are valid for any artificial barrier, water reservoir and civil structure which interferes with freshwater systems.

In cold climate regions, the formation and break-up of river ice is important for river morphology, winter water supply, and riparian and instream ecology as well as for hydraulic engineering. Data on river ice is therefore significant, both to understand river ice processes directly and to assess ice effects on other systems. Ice measurement is complicated due to difficult site access, the inherent complexity of ice formations, and the potential danger involved in carrying out on-ice measurements. Remote sensing methods are therefore highly useful, and data from satellite-based sensors and, increasingly, aerial and terrestrial imagery are currently applied. Access to low cost drone systems with quality cameras and structure from motion software opens up a new possibility for mapping complex ice formations. Through this method, a georeferenced surface model can be built and data on ice thickness, spatial distribution, and volume can be extracted without accessing the ice, and with considerably fewer measurement efforts compared to traditional surveying methods. A methodology applied to ice mapping is outlined here, and examples are shown of how to successfully derive quantitative data on ice processes.

Fish passing downstream through hydraulic structures and turbines may be exposed to an elevated risk of injury and mortality. The majority of live fish studies are single-species laboratory investigations and field studies of Kaplan turbines, with a limited number of studies in Francis and screw turbines. In addition to these studies, the physical conditions during turbine passage can be directly measured using passive sensors. In this study, we investigate the multispecies risk of injury and mortality during downstream passage through a large Archimedes hydrodynamic screw for bream (Abramis brama), eel (Anguilla anguilla), and roach (Rutilus rutilus) in conjunction with passive sensors that record the pressure, acceleration, and rate of rotation. This work proposes several new metrics to assess downstream passage including the times and durations of impact events, the kinetic energies of translation and rotation, and the pressure gradient. The major findings of this work are three-fold: (1) Significant differences in injury and mortality were observed between the three investigated species with 37% mortality for bream, 19% for roach, and 3% for eel on average. (2) The operational scenario was found to be significant only for a limited number of species-specific injuries and mortality rates. (3) In contrast to studies in Kaplan turbines, the sensor data revealed highly chaotic physical conditions in the Archimedes hydrodynamic screw, showing little difference in the physical metrics between operational scenarios.

Walking underwater reduces joint impacts, enhances stability and lowers the net body weight of the patient during rehabilitation. It is a recent rehabilitation method and few suitable methods exist to study underwater gait kinematics. We propose an underwater inertial measurement (IMU) system analogous to those used in land-based rehabilitation to investigate gait kinematics. The objective of this study was to test and validate the proposed system in two human trials by evaluating the knee angle during the gait. In the first trial, a three-way performance analysis was carried out between the IMU, optoelectronic and motion-capture systems in a traditional rehabilitation setting on land. In the second trial, the proposed underwater IMU is compared with camera-based motion-capture both inside and outside the water environment, using the same subjects in both phases of the trial. This allows for an evaluation of the walking gait in air and underwater as well as a cross-comparison of IMU-based knee angle estimates before and after Gaussian Process Regression. The major finding of this work is that the proposed underwater wearable IMU system provides reliable and repeatable measurements of the knee angle during the gait, both in air and underwater.