Impacts of implementation of Colombian environmental flow methodologies on the flow regime and hydropower production of the Chinchiná River, Colombia

We investigated the potential impacts on hydropower generation of applying six Colombian and two international best practice environmental flow methodologies within a small Andean river catchment, the Chinchiná River basin. Post-impact flow and hydropower production levels under the eight methodologies and a "no environmental flow scenario" were determined using a Microsoft Excel ^® flow diversion and hydropower production spreadsheet model. A flow regime alteration index (FRAI) was developed based on the degree of variation between the pre-and post-impact flow conditions of the 33 characteristic Indicators of Hydrologic Alteration flow regime parameters, facilitating a simplified comparison of the overall degree of alteration among the nine different environmental flow scenarios. Hydropower production decreased with increasing levels of environmental flow releases, with decreases of 16.9-76.4% relative to production levels in the absence of an environmental flow. None of the eight investigated methodologies maintained "sustainable" (<20%) levels of flow regime alteration while facilitating minimal reductions in hydropower generation. Methodologies which maintained sustainable flow regime alteration levels resulted in >50% decrease in hydropower production and >40% decrease in flow diversion capacity. We recommend a dual approach of hydropower re-operation and fine-tuning of existing national standards to consider the characteristic inter-and intra-annual seasonality and ecologically relevant flow events, maximizing benefits between power generation and environmental sustainability. Our findings are relevant to the Chinchiná River basin and regions of similar hydro-geographical conditions utilized for small scale hydropower production, and underscore the need for further development of existing environmental flow methodologies.