Moving waters to mitigate hydropeaking: A case study from the Italian Alps

Abstract

We assessed the effect of a hydropeaking diversion mitigation measure that allows for additional hydropower production, which markedly reduced hydropeaking on a 10-km stream reach in the north-eastern Italian Alps. Hydropeaking, caused by a storage hydropower plant, affected the study reach from the 1920s to 2015, when a cascade of three small run-of-the-river plants was installed to divert the hydropeaks from the plant outlet directly into the intake of the RoRs plants, and hydropeaking was released downstream the confluence with a major free-flowing tributary. The flow regime in the mitigated reach shifted from a hydropeaking-dominated to a baseflow-dominated regime in winter, with flow variability represented only by snowmelt and rainfall in late spring and summer. The application of two recently proposed sets of hydropeaking indicators, the hydraulic analysis of the hydropeaking wave, together with the assessment of biotic changes, allowed quantifying the changes in ecohydraulic processes associated with hydropeaking mitigation. The flow regime in the mitigated reach changed to a residual flow type, with much less frequent residual hydropeaks; although an average two-fold increase in downramping rates were recorded downstream the junction with the tributary, these changes did not represent an ecological concern. The functional composition of the macrobenthic communities shifted slightly in response to flow mitigation, but the taxonomic composition did not recover to conditions typical of more natural flow regimes. This was likely due to the reduced dilution of pollutants and resulting slight worsening in water quality. Conversely, the hyporheic communities showed an increase in diversity and abundance of interstitial taxa, especially in the sites most affected by hydropeaking.This effect was likely due to changes in the interstitial space availability, brought by a reduction of fine sediments clogging. Besides illustrating a feasible hydropeaking mitigation option for Alpine streams, our work suggests the importance of monitoring both benthic and hyporheic communities, together with the flow and sediment supply regimes, and physico-chemical water quality parameters.

Innovations in hydropeaking research

“…Greimel et al (2023) demonstrates the usability of PeakTrace, a tool to analyse hydropeaking hydrology that incorporates critical flow thresholds to expedite mitigation design. Bruno et al (2023) focuses on a hydropeaking diversion mitigation measure and assesses mitigation benefits by combining two sets of hydrological and biological hydropeaking indicators. Tena et al (2023) proposes a methodology to quantify hydropeaking regimes and assess the potential impacts on physical and biological components of river systems.…”

“…,Bakken et al (2023),Godinho et al (2023),Bruno et al (2023),Tena et al (2023),Reindl et al (2023),Halleraker et al (2023).3 | DISCUSSION3.1 | Key-word trendsTopics covered in this SI reflect the status of hydropeaking research, similar to that presented in Figure2, with dominance of eco-biological and engineering (i.e., physical processes) studies, and a lack of socio and economic-oriented contributions. To visually highlight possible shifts in the investigated topics, we present a cloud-word comparison between the Hauer et al (2017) SI and the current contributions (Figure3).…”

“…At the larger end of the reach scale, modelling approaches are mostly presented (e.g., Jelovica et al, 2023). Contributions on hydropeaking characterization and assessment covering larger spatial scales, that is, basin and/or regional, include Greimel et al (2023), Bakken et al (2023), Godinho et al (2023), Bruno et al (2023), Tena et al (2023), Reindl et al (2023), Halleraker et al (2023).…”

“…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). Tena et al (2023) in particular, used hydrological patterns related to hydropeaking to classify mountain rivers.…”

Short-term influences of flow alteration on microbial community structure and putative metabolic functions in gravel bar hyporheic zones

“…Limited studies focused on the effects of low regulation on microbial diversity in the hyporheic zone. One study focused on the altered flow regime as disturbance ecology (Bruno, et al, 2023). However, this study did not focus on differences in microbial community structure across different areas of hyporheic gravel bars.…”