Projects | Small Hydro Peaking
New research has looked at how hydropeaking by small hydropower facilities can affect flow regimes on tributaries to the Pantanal wetland in Brazil. Considering the rapid expansion of small hydropower development in tropical environments the authors say there is an urgent need to understand the ecological impacts of such hydropeaking
gauges not influenced by the facilities. Accordingly, relationships between the observed
hydrological alterations and the hydraulic and hydrological characteristics of rivers and hydropower facilities were also examined. These included installed potential, mean discharge, watershed area, reservoir area, hydraulic residence time, diverted natural channel length, and dam design.
Above: Map of the Upper Paraguay River Basin showing the distribution of river gauging stations upstream and downstream of currently operating hydropower facilities, indicating the stations with data gaps of <20% that allowed upstream-downstream comparisons for 24 hydropower facilities. The map also shows future hydropower projects that are either under construction, planned, or identified as potential sites for hydropower development in the Pantanal watershed by either the Brazilian National Electric Energy Agency or the state environmental agencies (depending on location)
HYDROELECTRIC FACILITIES OFTEN RELEASE water at variable rates over the day to match electricity demand, resulting in short-term variability in downstream discharge and water levels. Authors of new reach published in Frontiers in Environmental Science say that such hydropeaking has mostly been studied at large facilities. However, the proliferation of small hydro facilities in Brazil (5-30MW) has raised the question of how they may alter downstream flow regimes by hydropeaking. The study by Figueiredo et al examines the individual and cumulative effects of hydropower facilities on tributaries in the upland watershed of the Pantanal on the upper Paraguay River, located mostly in Brazil. It iforms part of a multidisciplinary research programme that has examined the issues surrounding hydroelectric facilities here, including hydrology, sediment transport, water quality, and fish and fisheries. As the authors state: “Hydrological effects of SHPs are of
particular concern in the upland watershed of the Pantanal, a world-renowned floodplain wetland system…. While the effects of hydropeaking are unlikely to extend into the floodplains due to longitudinal attenuation, the unnatural sub-daily variability in river flow regimes in reaches downstream of SHP facilities could affect behaviour and reproduction of fishes that migrate upstream from the Pantanal, in addition to resident fishes and other aquatic and riparian organisms.” In this study, evidence for hydropeaking was evaluated based on discharge patterns in river gauges downstream of 11 reaches containing a total of 24 hydropower facilities, compared to simultaneous measurements at reference
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Comparison of daily data over an annual period, summarised by indicators of hydrological alteration (HA) that describe the magnitude, frequency, rate of change, and duration of flows, revealed differences at sub-daily scales attributable to hydropeaking by the hydro facilities. Results showed statistically significant sub-daily HA in all 11 reaches containing hydro facilities in all months. The authors say that their study demonstrates that SHPs, as well as larger hydropower facilities, cause hydrological alterations attributable to hydropeaking. Considering the rapid expansion of SHPs in tropical river systems, there is an urgent need to understand whether the ecological impacts of hydropeaking documented in temperate biomes also apply to these systems. “This will be challenging because life cycles and behaviour of the aquatic biota in tropical rivers in relation to river hydrology are less well-understood and even migration routes of fishes that support socioeconomically valuable fisheries are incompletely known. “It is obvious that the aquatic biota will likely be harmed by abrupt decreases in water levels causing stranding of fishes and other aquatic animals as well as the temporary emergence of aquatic substrata that would otherwise remain underwater. However, changes in depth and wetted area of the river channel as a result of hydropeaking depend on channel morphology - information that is lacking for the rivers we study here, as it is for most other regions of the world where SHPs are proliferating.” The authors also add that planning for new SHP locations and designs needs to consider how the resultant hydrological modifications may negatively affect migratory fishes and other aquatic animals, not only by producing barriers and directing most of the flow through turbines, but also altering downstream hydrology. Such planning should be conducted at the scale of entire river basins to minimise negative impacts on migratory populations. ●
Reference Hydropeaking by Small Hydropower Facilities Affects Flow Regimes on Tributaries to the Pantanal Wetland of Brazil by Juliane Stella M. C. de Figueiredo, Ibraim Fantin-Cruz, Geovanna Mikaelle S. Silva, Renato Leandro Beregula, Pierre Girard, Peter Zeilhofer, Eduardo Morgan Uliana, Eduardo Beraldo de Morais, Hans M. Tritico, Stephen K Hamilton. Frontiers in Environmental Science Vol 9 2021.
www.frontiersin. org/article/10.3389/fenvs.2021.577286
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