Effects of small hydropower plants in cascade arrangement on the discharge cyclic patterns

Abstract

Because it is assumed that the impacts in the natural streamflow regime promoted by Small Hydropower Plants (SHP) are negligible, environmental licensing for such facilities is usually easier. Nonetheless, recent studies have shown that the operation of SHPs may disturb the natural flow conditions, mainly when the plants are placed in a cascade arrangement. In this context, the main objective of this study is investigating the alterations in flows periodic behavior in a system of six hydropower plants, being five of them SHPs. Daily discharge time series were extracted from eight streamflow gauging stations located in the Jauru River catchment, Brazil, whose period-of-record spans from May/2016 to Aug/2017. By using the wavelet transform, dominant cycles along the time series were identified and their coherence in nearby stations was compared. Among the results, one may observe that, from upstream to downstream, the high frequency cycles became more important whereas the low frequency ones have weakened. Additional analyses indicate that such alterations are not directly related to meteorological factors or to the gradual increasing in the catchment's drainage area in the downstream direction, which suggests that the operation of SHPs may affect the streamflow natural cycles. RESUMOPor assumir que os impactos nos regimes naturais de vazão de Pequenas Centrais Hidrelétricas (PCHs) são desprezíveis, os licenciamentos ambientais para esses empreendimentos são relativamente fáceis de serem obtidos. Contudo, estudos recentes têm mostrado que a operação de PCHs pode afetar as condições naturais de escoamento especialmente quando os aproveitamentos hidrelétricos são alocados em cascata. Nesse contexto, o principal objetivo deste trabalho é investigar a alteração do comportamento das periodicidades de vazões em um sistema com seis aproveitamentos hidrelétricos, sendo cinco PCHs. Foram utilizadas séries de vazões diárias extraídas de estações localizadas na bacia do rio Jauru, na região hidrográfica do Alto Paraguai, Brasil, entre maio de 2016 e agosto de 2017. Por meio da transformada wavelet, foi possível identificar ciclos dominantes ao longo do tempo e comparar a coerência de séries de vazões entre estações adjacentes. Entre os resultados, observou-se que, no sentido de montante para jusante, os ciclos de alta frequência se tornam mais evidentes enquanto aqueles de baixa frequência ficam enfraquecidos. Análises adicionais indicaram que tais alterações não estão diretamente relacionadas a fatores meteorológicos ou ao aumento gradual da área de drenagem da bacia na direção a jusante, o que sugere que a operação das PCHs pode afetar o ciclo natural de vazões.Palavras-chave: Periodicidade de vazão; Transformada wavelet; Impacto de pequenas barragens; Usina a fio d'água; Análise de séries temporais.RBRH, Porto Alegre, v. 24, e33, 2019Effects of small hydropower plants in cascade arrangement on the discharge cyclic patterns 2/15

Predicted impacts of proposed hydroelectric facilities on fish migration routes upstream from the Pantanal wetland (Brazil)

“…A second point to consider is that while this paper has focused on the proposed dams' impacts on fish migration, it is likely that the presence of dams will impact hydrology and sediment transport functions within the watershed. Existing studies within the basin indicate that the nearly run of the river dams do not substantially alter the long temporal scale (weekly or monthly) hydrology but may influence the sub‐daily hydrology (de Paes et al, ; Fantin‐Cruz et al, ; Zeilhofer & de Moura, ). Given that most spawning happens at night, the sub‐daily adjustments may still impact spawning behavior downstream from the proposed dams (Ziober et al, ).…”

Impacts of the landscape changes in the low streamflows of Pantanal headwaters—Brazil

“…From then on, the streamflows patterns in stations 5, 6 and 7 showed signs of interference by operations in lakes and reservoirs (i.e. Ely et al, 2020; Kuriqi et al, 2021; Paes et al, 2019). Notwithstanding, it is important to note that in the series of streamflows in station 7, where it is the mouth of the whole basin, negative trends were significant during the dry season in the period of 1985 to 2005 which was prior to the building of a large reservoir in Jauru River and concomitant with the expansion of pasture areas in the basin.…”

“…Also, there is a regularity of the minimal streamflows at these stations after the 2000s. This behaviour is a result of reservoir management in the hydroelectric enterprises of the Jauru River (Paes et al, 2019).…”

“…From then on, the streamflows patterns in stations 5, 6 and 7 showed signs of interference by operations in lakes and reservoirs (i.e. Ely et al, 2020;Kuriqi et al, 2021;Paes et al, 2019).…”

Sub-daily flow alterations (hydropeaking) due to reservoir operations in Brazil

“…The Jauru River, in the state of Mato Grosso, has a series of hydroelectric plants that operate with hydropeaking, meaning they release flow with rapid fluctuations on a sub-daily time scale, which are not typically present in the natural hydrological regime, as demonstrated by Paes et al (2019) and Figueiredo et al (2021).…”