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.