Integrating two‐dimensional water temperature simulations into a fish habitat model to improve hydro‐ and thermopeaking impact assessment

Abstract

Storage hydropower plants, which are an important component of energy production in Switzerland, can lead to hydro-and thermopeaking, affecting river habitats and organisms. In this study, we developed an approach for integrating water temperature simulations into a habitat model to assess the impact of both hydro-and thermopeaking on the availability of suitable fish habitats. We focused on the habitat requirements of juvenile brown trout (Salmo trutta) in a semi-natural braided floodplain along the Moesa River (Southern Switzerland) in early summer. First, we defined different scenarios (with and without hydropeaking) based on the local hydrological and meteorological conditions. Second, we used a two-dimensional depth-averaged hydro-and thermodynamic model to simulate the spatial distributions of water depth, flow velocity, and water temperature. Third, we applied generalized preference curves for juvenile brown trout to identify hydraulically suitable habitats, and developed a new index to assess the availability of thermally suitable habitats. Finally, we quantified the extent to which hydraulically and thermally suitable habitats overlap in space and time. During both base and peak flow phases, most of the hydraulically and thermally suitable habitats are located in the side channels. High flow conditions combined with strong cold-thermopeaking lead to a higher thermal heterogeneity. However, disconnected habitats originate in the dewatering zone, increasing the risk of stranding as well as thermal stress. By helping to better understand the effects of thermopeaking on the availability of fish habitats, our approach could contribute to the design and evaluation of ecological restoration in hydropeaking rivers.

Applying a two‐dimensional hydrodynamic model to estimate fish stranding risk downstream from a hydropeaking hydroelectric station

“…We found that the presence of young‐of‐the‐year fish greatly influenced the stranding rate, and if mitigation is applied to months with higher numbers of young‐of‐the‐year fish, the risk of stranding can be reduced by implementing a minimum flow and reducing ramping rates (Hayes et al, 2019). Additionally, reducing the up‐ and down‐ramping of the station may result in increased time for fish to seek new stable habitats reducing the number of fish stranding (Antonetti et al, 2022); however, Glowa et al (2022) found that the ramping rate did not affect fish stranding potential.…”

Innovations in hydropeaking research

“…Ten contributions provided exhaustive analysis of field data, based on either single sites (e.g., Abernethy et al, 2023;Bartoñ et al, 2023;Boavida et al, 2023;Judes et al, 2023;Pander et al, 2023), or comparisons between several sites (e.g., Halleraker et al, 2023;Tena et al, 2023;Tonolla et al, 2023) Different modelling approaches are presented in the SI: from hydraulic, temperature, and habitat modelling (e.g., Antonetti et al, 2023;Jelovica et al, 2023;Judes et al, 2023), to rule-or processbased classification tools (e.g., Bakken et al, 2023;Godinho et al, 2023;Greimel et al, 2023;Reindl et al, 2023), to individual-based models (Hajiesmaeili et al, 2023). Two contributions specifically focus on numer- single contribution examines the use of remote sensed data for the investigation of fish stranding in a large river (Glowa et al, 2023).…”

“…Eight articles focus on abiotic components, hence investigating and quantifying physical processes and alterations related to hydropeaking. Temperature alterations (i.e., thermopeaking) are specifically considered in (Auer et al, 2023) and (Antonetti et al, 2023). Hydrological and hydraulic characterization of hydropeaking is considered in several contributions of the SI (e.g., Auer et al, 2023; Boavida et al, 2023; Bruno et al, 2023; Greimel et al, 2023; Judes et al, 2023; Reindl et al, 2023).…”

“…Different modelling approaches are presented in the SI: from hydraulic, temperature, and habitat modelling (e.g., Antonetti et al, 2023; Jelovica et al, 2023; Judes et al, 2023), to rule‐ or process‐based classification tools (e.g., Bakken et al, 2023; Godinho et al, 2023; Greimel et al, 2023; Reindl et al, 2023), to individual‐based models (Hajiesmaeili et al, 2023). Two contributions specifically focus on numerical hydrodynamic models: Bürgler et al (2023) presents a systematic comparison of 1D and 2D models, whilst Le Coarer et al (2023) proposes a new algorithm to enhance the quantification of stranding risk.…”

“…When focusing on the biotic compartment, fish are a primary consideration, with investigations covering different life‐history traits: from spawning (Pander et al, 2023), to juveniles (Antonetti et al, 2023; Auer et al, 2023), and adults (Bakken et al, 2023). Salmonid species, which have received long‐lasting attention probably due to their economic value, are still dominant (Antonetti et al, 2023; Auer et al, 2023; Bakken et al, 2023; Hajiesmaeili et al, 2023; Halleraker et al, 2023; Jelovica et al, 2023; Pander et al, 2023); nevertheless the attention on cyprinid species has increased (Bartoñ et al, 2023; Boavida et al, 2023; Godinho et al, 2023; Judes et al, 2023).…”