Sub-daily Hydrological Regime Alteration due to Hydropower generation in three river basins in Central Chile

Central Chile Andean catchments sustain several water uses, including both run-of river and reservoir-based hydropower plants. Hydropower is a non-consumptive water use; however, it induces alterations in the flow regime at different time and spatial scales. Hydropeaking is an operational scheme characterized by frequent, rapid, and short-term fluctuations in water flow and water levels downstream and upstream of hydropower stations. This impacts the ecological processes in river ecosystems and creates operational interferences with other downstream users.

In this work, we study hydropower operations and its effect on the streamflows at relevant locations in major rivers in Central Chile. We analyze three different case studies: a complex configuration of 5 run-of-river hydropower plants at Maipo River, a series of 2 run-of river plants at Tinguiririca River, and a cascade of 3 reservoir hydropower plants at Biobio River. We apply common ecological meaningful metrics of sub-daily hydrologic alteration (Richards-Baker Flashiness Index, Coefficient of diel variation, and % of total flow) to multi-year hourly streamflow series, to characterize the hydrological regimes and the effect of different operational schemes. Based on data availability of each case study, we propose alternative approaches for the analysis. We then compare results among basins, operational schemes, and type of hydropower plant. Preliminary results show that all hydropower plants in every basin operate under hydropeaking scheme, regardless of their run-of-river or reservoir nature, although with different magnitude and patterns. Reservoir-based plants show more fluctuating operations than run-of-river, with sub-daily indicators up to 3 times higher. The observed hydropeaking operation scheme reflects itself in the downstream hydrological regime, as hydrologic alteration indicators applied to the hydropower flows and downstream streamflows behave similarly. We discuss the limitations encountered due to streamflow data resolution and availability. Results are of interest to ecohydrology studies that aim to understand the ecological implications of sub-daily flow changes.