An increase in the demand for renewable energy is driving hydropower development and its integration with variable renewable energy sources. When hydropower is produced flexibly from hydropower plants, it causes rapid and frequent artificial flow fluctuations in rivers, a phenomenon known as hydropeaking. Hydropeaking and associated hydrological alterations cause multiple impacts on riverine habitats with cascading effects on ecosystem functioning and structure. Given the significance of its ecological and socio‐economic implications, mitigation of hydropeaking requires an inter‐ and transdisciplinary approach. An interdisciplinary network called HyPeak has been conceived to enrich international research initiatives and support hydropower planning and policy. HyPeak has been founded based on exchange and networking activities linking scientists from several countries where hydropeaking has been widespread for decades and numerous studies dedicated to the topic have been carried out. HyPeak aims to integrate members from other countries and continents in which hydropower production plays a relevant role, and grow to be a reference group that provides expert advice on the topic to policy‐makers, as well as researchers, stakeholders, and practitioners in the field of hydropeaking.
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.
Sudden instream releases of hypolimnetic water from hydropower plants [i.e. hydropeaking (HP)] can cause abrupt temperature variations [i.e. thermopeaking (TP)], typically on a daily basis. The propagation of discharge and thermal waves is asynchronous, causing the benthic community to undergo two different but consecutive impacts. Invertebrates respond to sudden increases in discharge with catastrophic drift, and respond to sudden changes of temperature with behavioural drift. Owing to the time lag separating discharge and thermal wave peaks, catastrophic and behavioural drift can occur as distinct events. We conducted simulations in a set of open air flumes directly fed by an Alpine stream, and analysed drift induction in benthic invertebrates caused by a HP wave followed by a cold TP wave, and compared it with drift induced only by a cold TP wave. Drift propensity increased during HP and TP simulations, with a synergic effect: drift was higher when the TP wave followed the HP one. We also recorded a selective effect: some taxa did not respond to the alterations, some taxa responded to the discharge variations and to the thermal variations, or to the thermal variations alone. The most abundant taxa in benthos were Chironomidae and Baetidae, followed by Simuliidae. Simuliidae and Chironomidae were the most abundant drifting taxa. Copyright © 2012 John Wiley & Sons, Ltd.
Changes in flow regime associated with sharp discharge fluctuations when water is released from the hydropower plants into the streams (hydropeaking) have cascading effects on the ecological integrity of riverine ecosystems. Hydropeaking modifies the specific composition and longitudinal zonation of invertebrate populations downstream of the power plants through direct impacts on the benthic fauna due to scouring, which removes the animals through drift (i.e. the downstream transport of aquatic organisms under the effect of current velocity) and indirect impacts on the hyporheic zone, i.e. clogging of the interstitial spaces. Clogging occurs due to the reduction of flow and extreme flood events and by deposition of the fine material transported by the release of hypolimnetic water. Clogging reduces the throughflow and the concomitant delivery of resources, as well as the usable pore space for interstitial fauna, impacting the colonization dynamics of interstitial animals. While the impacts of hydropeaking on benthic organisms have been widely investigated so far those on hyporheic fauna have seldom been studied. In a previous research conducted in the same stations discussed here, we investigated the effects of one single hydropeaking event on benthic and hyporheic invertebrates, and assessed that the hyporheic habitat was used as a refuge to avoid drift by part of the benthic organisms, and that hydropeaking reduced hyporheic diversity and abundance in impacted sites, especially affecting the stygobites (specialised subterranean forms, obligatory hypogean), which were significantly more abundant at the non-impacted site. We continued the investigations by studying the spatial (downstream from the disturbance) and temporal effects of repeated hydropeaking events on hyporheic communities. We focussed on the specialization level of the organisms to life in the groundwater, based on the assumption that a reduction of the available habitat for stygobite taxa due to colmation would reduce their abundance. On the other hand, in reaches where the effect of increased discharge is the removal of benthic invertebrates through catastrophic drift, the abundance of the stygoxenes in the hyporheic would increase, because such organisms use the hyporheic habitat as a refuge. Thus, our study aimed to assess the following working hypotheses for aquatic invertebrate responses to repeated hydropeaking waves: 1. Repeated hydropeaking events alter and reduce the habitat available to hyporheic organisms impacting the hyporheic invertebrate communities 2. The hyporheic habitat represents a refuge for benthic taxa to avoid catastrophic drift; 3. The disturbance caused by the turbinated water releases propagates several kilometres downstream. The impact of repeated hydropeaking events was assessed in the Alpine stream Noce Bianco. Three stations were selected, one upstream and two at 0.25 km and 6 km downstream from a hydropower plant which causes 7-fold discharge increases. We collected hyporheic invertebrates for two years. The results confirmed our hypotheses: hydropeaking reduced hyporheic diversity and abundance in impacted sites, especially affecting the stygobites, which were significantly more abundant at the non-impacted site. Stygoxene invertebrates were exponentially more abundant at the impacted sites, indicating that the hyporheic habitat was used as a refuge to avoid catastrophic drift by part of the benthic organisms. The results were possibly due to the colmation of the interstitial space downstream of the power plant, caused by the deposition of the fine sediment transported by the turbinated water and the absence of natural peak floods.
The impact of a single hydropeaking event was studied in the Alpine stream Noce Bianco. Four stations were selected, one upstream and three, respectively, at 0.25, 6, and 8km downstream from a hydropower plant. We collected drifting invertebrates during a planned water release that increased the discharge 7-fold. At the onset of the hydropeaking wave the number of invertebrates lost from the riverbed per minute to the drift increased 9-fold at the first downstream station and the same effects propagated 8km downstream. The drift was composed mainly of aquatic insect larvae (Chironomidae, Plecoptera, Ephemeroptera Baetidae, and Psychodidae, with Chironomidae as the most abundant taxon at all stations) and partly by larval and adult riparian insects, and by Oligochaeta, which were particularly abundant at the station 6km downstream. We monitored drift for 30min from the start of the water release: peaks in drifting invertebrates occurred within 5–10min of the beginning of the hydropeaking wave, and most of the invertebrates were washed out within the first 15min of the water release. The different timeframes were possibly due to habitat preferences (most of the taxa that increased in the drift at the arrival of the wave were associated with algae and organic debris, which were washed off quickly by the increase in discharge) and/or behavioral adaptations (other taxa initially resisted the shear stress and began to drift with a delay of 5–10min). The temporal pattern and drift composition corresponded well with those reported in literature, and indicate that repeated high-flow events of similar magnitude cause considerable losses from benthic populations to drift.
Rivers of the large Alpine valleys constitute iconic ecosystems that are highly threatened by multiple anthropogenic stressors. This stressor mix, however, makes it difficult to develop and refine conservation and restoration strategies. It is, therefore, urgent to acquire more detailed knowledge on the consequences and interactions of prevalent stressors on fish populations, in particular, on indicator species such as the European grayling Thymallus thymallus. Here, we conducted a multi-river, multi-stressor investigation to analyze the population status of grayling. Using explorative decision-tree approaches, we disentangled the main and interaction effects of four prevalent stressor groups: flow modification (i.e., hydropeaking), channelization, fragmentation, and water quality alteration. Moreover, using a modified variant of the bootstrapping method, pooled bootstrapping, we determined the optimal number of characteristics that adequately describe fish population status. In our dataset, hydropeaking had the strongest single effect on grayling populations. Grayling biomass at hydrological control sites was around eight times higher than at sites affected by hydropeaking. The primary parameters for predicting population status were downramping rate and peak amplitude, with critical ranges of 0.2–0.4 cm min⁻¹ and 10–25 cm. In hydropeaking rivers, river morphology and connectivity were the preceding subordinated parameters. Repeating the procedure with pooled bootstrapping datasets strengthened the hypothesis that the identified parameters are most relevant in predicting grayling population status. Hence, hydropeaking mitigation based on ecological thresholds is key to protect and restore already threatened grayling populations. In hydropeaking rivers, high river network connectivity and heterogenous habitat features can dampen the adverse effects of pulsed-flow releases by offering shelter and habitats for all life cycle stages of fish. The presented approach of explorative tree analysis followed by post-hoc tests of identified effects, as well as the pooled bootstrapping method, offers a simple framework for researchers and managers to analyze multi-factorial datasets and draw solid management conclusions.
As the demand for hydroelectricity progresses worldwide, small hydropower operators are increasingly examining the feasibility of using existing infrastructure (e.g., settling basins) in run-of-the-river schemes for intermittent power production. Such flexible production causes short-term discharge fluctuations (hydropeaking) in downstream reaches with potential adverse effects for the sensitive fauna and flora in alpine streams. In an experimental field study on a previously unregulated section of the upper Rhone River (Switzerland), we measured density and composition of macroinvertebrate drift in two habitats (riffle, pool) following a 15-minute hydropeaking wave. The experimental hydropeaking was replicated five times over 14 days with decreasing recovery times between peaks (8, 3, 2 days, and 24 h), and drift measurements were compared with kick samples for the benthic community. Results from the kick sampling showed that benthic macroinvertebrate abundance and composition did not significantly change between the experimental peaks. There were habitat specific reactions in macroinvertebrate drift to hydropeaking, with the pool experiencing more pronounced drift abundances than the riffle. Overall, drift abundance was not significantly correlated with recovery time, but results indicate taxa-specific differences. This research advocates for the importance of completing more in-situ field experiments in order to better understand the ecological impact of flexible power production in small hydropower plants.
Hydropeaking research has generated unprecedented scientific discussion in the last twenty years and improved our understanding of the processes resulting from hydropeaking by strengthening the links between basic knowledge and practical applications. Given the reportedly increase in hydropeaking operations and applications in recent years, this Special Issue aims to explore the most up-to-date innovations in hydropeaking with a focus on approaches leading to quantify processes. All disciplines working in hydropeaking-related issues will be considered, from hydrology, hydraulics, fluvial geomorphology, freshwater and terrestrial ecology, landscape planning to social sciences, economics, and market drivers. Interdisciplinary and transdisciplinary approaches and perspectives will be particularly welcome. Abstract submission deadline (via direct email to guest editors): May 1st, 2021 Abstract acceptance notification: May 15th, 2021 Full paper submission deadline: November 30th, 2021 (Early submissions are encouraged) Tentative date for SI online publication*: January 31st, 2022 *please note that individual papers will be given a DOI and published online as soon as they are accepted. More details can be found here: https://onlinelibrary.wiley.com/page/journal/15351467/homepage/call-for-papers-innovations-in-hydropeaking-research