Trapped between drowning and desiccation: Riverine plants under hydropeaking.

Hydropeaking is part of hydropower production. The discontinuous release of turbined water during hydropeaking generates sudden rise and falls of the water levels, as well as extended droughts. These artificial flow fluctuations impose challenging growing conditions for riverine vegetation. In order to identify vulnerable/resistant plant species to hydropeaking and to evaluate the impact of contrasting hydropeaking scenarios (simplified (i.e., sudden deep floods, frequent soil saturation and drought) and real-life, power plant-induced scenarios), we measured germination, survival, and morphological and physiological attributes of a selection of 14 plant species commonly found along riparian areas. Species were subject to different hydropeaking scenarios during three months (vegetative period) in the field and in a greenhouse. Half of the species performed worse under hydropeaking in comparison to the control (e.g., less germination and biomass, lower growth rates, reduced stem and root length, physiological stress) but none of the tested hydropeaking scenarios was clearly more disruptive than others. Betula pubescens, Alnus incana and Filipendula ulmifolia showed the largest vulnerability to hydropeaking, while other species (e.g., Carex acuta) were resistant to it. Both in the field and in the greenhouse, plants in perturbed scenarios accumulated more 13C than in the control scenario indicating limited capacity to perform 13C isotope discrimination and evidencing plant physiological stress. The highest 13C abundances were found under drought or flooding conditions in the greenhouse, and under the highest hydropeaking intensities in the field (e.g., Betula pubescens). Our results suggest that any hydropeaking scheme can be equally detrimental in terms of plant performance. Hydropeaking schemes that combine periods of severe drought with long and frequent flooding episodes may create a hostile environment for riverine species. Further research on "hydropeaking-tolerant" plant traits is key to draw the boundaries beyond which riverine species can germinate, grow and complete their life cycle under hydropeaking.

Can vegetation provide shelter to cyprinid species under hydropeaking?

A novel study that focuses on the capacity of vegetation to provide shelter for fish species under hydropeaking regimes is presented. Two artificial patches mimicking the structure and density of Carex sp. mats were installed in an experimental flume to test whether submerged plants can offer flow refuge to two cyprinid species, Luciobarbus bocagei and Pseudochondrostoma polylepis, under baseflow and hydropeaking scenarios. Local flow fields were characterized using a Lateral Line Probe (LLP) and an Acoustic Doppler Velocimeter (ADV) and 33 h of video analysis were viewed to report, on a per-second basis, fish use of 1) patches with plants, 2) patches upstream and 3) downstream from vegetation and 4) patches without vegetation. Data on flow fields and fish patch use were integrated and analyzed to assess whether plants favored fish sheltering behavior. Vegetation created hydraulically stable areas suitable for fish to shelter, triggering changes in fish patch use. Although both species sheltered under hydropeaking, L. bocagei presented a stronger preference than P. polylepis for vegetated patches and areas downstream from plants, taking advantage of sheltered regions more frequently. P. polylepis weaker search for shelter could be related to species-specific factors and territorial behavior interferences rather than to fish performance relative to flume hydraulic conditions. Despite a weaker response, some P. polylepis individuals used patches downstream from plants more during the second half of the hydropeaking trials. A trade-off between reducing swimming effort and territoriality might explain this response. Results indicate that vegetation can help to counterbalance the impact of hydropeaking on fish while providing river functioning benefits. Evaluating fish sheltering to a wide set of river plants and patch designs on a species-by-species basis would help targeting vegetation-based actions for restoring hydropeaking rivers.

E-flows to reduce the hydropeaking impacts on the Iberian barbel (Luciobarbus bocagei) habitat. An effectiveness assessment based on the COSH Tool application.

Hydropower plant (HPP) operations, in response to variations in market energy demand and electricity production, can generate rapid and frequent fluctuations of discharge in rivers downstream. This phenomenon, termed hydropeaking, may negatively impact fish populations. The present study aims to investigate the effects of hydropeaking on the Iberian barbel (Luciobarbus bocagei) habitat conditions. A two-dimensional (2D) model was used to obtain the habitat suitability downstream of a HPP. The influence of the ecological flow (E-flow) regime on the habitat conditions and flow fluctuations owing to hydropeaking was assessed. COSH-Tool was applied to the sub-daily flow series to quantify and characterize the rapid fluctuations (with and without an E-flow regime) with the purpose of assessing the impacts on fish habitat. The monthly distribution of peaking events showed a marked seasonal pattern associated with the Mediterranean climate, with most of the rapid fluctuations concentrated during the wet season. A peaking event occurred within three days of the low flow period. Approximately 80% of the 10-year time series returned a zero value of discharge (no power production). The median of the rates of stage (water level change during an increase or decrease of flow divided by the time of that change) resulted in 30.7 and 28.3 cm/h when the E-flow regime was not considered, and the rate of change was 26.3 and 22.4 cm/h when the E-flow regime was considered respectively for rapid increases and decreases. The flow ratio (peak flow divided by base flow) obtained for the E-flow regime was 334.3. Results showed that the hydrologic parameters associated with hydropeaking are attenuated with the E-flow regime. In certain cases, the E-flow regime should be regarded as an alternative mitigation measure for rivers subjected to hydropeaking.

Ecologically-based criteria for hydropeaking mitigation: A review.

Hydroelectric power plants managed in response to sub-daily changes of the electricity market undergo rapid variations of turbine discharge, entailing quickly fluctuating water levels downstream. This operation regime, called hydropeaking, causes numerous adverse impacts on river ecosystems. The hydrological alterations which affect hydropeaking rivers can be described by five parameters that change over space and time (magnitude, rate of change, frequency, duration, and timing), where each parameter may be correlated with distinct environmental impacts and therefore may be used to define flow thresholds and set targets for operational mitigation strategies. Thus, this study aims to present an extensive review on the so far established hydropeaking targets and thresholds regarding the outputs from the scientific community as well as from national regulations. We found that only few European countries (Switzerland and Austria) have legal regulations regarding hydropeaking flow thresholds. Other countries, such as Canada and the USA, present environmental legislation that can force hydropeaking mitigation measures. Most mitigation thresholds and management recommendations in literature deal with the effect of downramping on the stranding of salmonids, as well as with minimum flows between peak-flows to avoid spawning ground desiccation. Regarding other fish species and parameters, information on mitigation targets or thresholds is scarcer or non-existent, as well as on hydropeaking mitigation case-studies, resulting in a lack of knowledge and guidelines for its implementation or regulation. Nevertheless, the available literature indicates that multiple aspects must be considered when assessing such values. Thus, to aid in that process, we propose that mitigation targets and thresholds must be based on key species, including particular features regarding season, life-stage and time of day, which must be combined with site-specific morphological characteristics. The presented approach may benefit impacted organism groups in hydropeaking reaches through the establishment of ecologically-based relevant mitigation thresholds and/or targets.

Fulfilling spawning flow requirements for potamodromous cyprinids in a restored river segment.

The Baixo Sabor hydroelectric scheme was recently constructed (began operating in 2015), blocking fish migration immediately at the river mouth. As a compensation measure for spawning habitat loss the Vilariça River which confluences with Sabor River, immediately downstream from the Baixo Sabor scheme, was chosen for rehabilitation site as an attempt to replace the spawning grounds lost in Sabor River for the potamodromous cyprinid Iberian barbel (Luciobarbus bocagei). Restoration activities included: placement of submerged weirs with fish ramps to increase the lotic/lentic sequence, bank reinforcement, boulder placement and river water profile increase. Water from the nearest reservoir was channeled underground to the lower Vilariça River in order to increase the water flow. The most appropriate volume of water was determined by means of a 1D model coupled with the CASiMiR to determine the weighted usable area for barbel spawners. Nine spawning grounds were identified. Fish migrations began in mid-April when water temperature increased (c. 16°C) and water flow decreased. Barbel tend to spawn in coarse substrate with shallow water and moderate current. Ontogenetic differences in habitat use were reported, with barbel juveniles preferring weaker currents and deeper zones when compared to spawners. Females also display different preferences, which are more apparent after spawning. Both life-stages exhibit the maximum habitat suitability at c. 1.5m3/s. The habitat model used in this study was able to accurately predict the occurrence of spawning grounds, representing, therefore, a valuable decision-making support tool for river managers.