Extreme, short-duration fluctuations caused by hydropeaking occurs when hydropower is regulated to cover demand peaks in the electricity market. Such rapid dewatering processes may have a high impact on the downstream biological conditions, particularly related to stranding of fish and other species. The present work analyzes these fluctuations using a two-dimensional unsteady hydraulic modelling approach for quantification of two important hydro-morphological factors on fish stranding risk: the variation in wetted area and the dewatering ramping rate. This approach was applied on the two-kilometer-long reach of Storåne downstream of the Hol 1 power plant, where topo bathymetric LiDAR (Light Detection and Ranging) data was available providing a high-resolution digital elevation model. Based on this model, hydraulic conditions could be simulated in high detail allowing for an accurate assessment of the hydro morphological factors. Results show the dried area distribution at different flows and dewatering ramping rates. The attenuation of the water level fluctuation due to the damping effect along the river reach controls the dewatering rate. We recommend an alternative scenario operation which can reduce the impact of the peaking operation and estimate the operational mitigation cost. We find that the modelling based on the fine resolution grid provides new opportunities in assessing effects of hydropower regulations on the ecosystem.

No abstract

Water temperatures control life histories and diversity of aquatic species. Hydropower regulation, particularly in high head systems, alters natural water temperature regimes, which may have profound and long-term impacts on aquatic environments. Temperatures in by-pass sections and reaches affected by residual/environmental minimum flows fluctuate more than in natural flow regimes, driven more by influence of air temperatures. Reaches downstream of power plant outlets tend to become warmer in winter and colder in summer, driven by stratification behind the reservoir dam. In hydro-peaked systems high-low temperature effects may thus be aggravated. We review alterations of hydropower to natural thermal regimes, impacts on key organisms in terms of survival, development and behavioral thresholds, and potential mitigation measures, with focus on Atlantic salmon and brown trout in high northern latitude stream systems. Previous syntheses have focused mainly on flow changes and ecological impacts. Temperature effects may not always be correlated with flow changes, although there are some unique challenges with temperature changes in far northern latitudes, for example, related to the seasonal and colder climates. To help knowledge-based management and identify potential knowledge gaps, we review how hydropower regulation may impact seasonal water temperatures, what impacts changes to stream system temperature regimes may have to key organisms, for example, Atlantic salmon and brown trout, and what adaptations and behavioral variations they may exhibit to respond to changed temperature regimes, and finally what good practices can be recommended for mitigating temperature impacts. This synthesis indicates that there are impacts to the fish and their supporting food webs, in particular related to growth and development, and the potential for negative impacts seems higher, and better studied, than positive impacts in northern river systems. Some of these impacts may be modified by directed hydropower regulation practices, but here effect studies and knowledge are limited.

Early career researchers (ECRs) play a critical role in our increasingly knowledgebased society, yet they are the most vulnerable group in the scientific community. As a relatively young, interdisciplinary science, ecohydraulics is particularly reliant on ECRs for future progress. In 2014 the Early Careers on Ecohydraulics Network (ECoENet) was created in order to help the development of young researchers working in this field. In this paper we synthesise the outcomes of a workshop for ECRs organised by ECoENet in February 2016. We aim to show how the potential of ECRs can be maximised in order to drive progress in ecohydraulics. According to the most recent entrants to the field, major challenges in ecohydraulics lie in becoming more integrated as a discipline, developing a common vocabulary and a collective vision, engaging effectively with policy makers, and encouraging public participation. To address these challenges in the future, ECRs need to develop their careers on an international scale in a way that crosses traditional disciplinary boundaries, including the social sciences, and allows them time to work at fundamental levels rather than focusing solely on individual applications. Herein, we propose a strategy to facilitate this by providing: a platform for disseminating research; an international support network; and a set of international services for enhancing ECR training and experience.