The objective was to develop a glacio-hydrological assessment for planned run-of-river hydropower plant locations in the Nakhraa river basin in Georgia. The availability of observed river flow data is limited. Hence the assessment was developed based on hydrological simulations of the basin using the SPHY model (Terink et al., 2015). State-of-the-art global datasets were used for the biophysical input requirements of the hydrological model including the extent of glaciers. The model was calibrated with the available river flow data and then extended for a period of 36 years (1980-2015) at the locations of interest. The main output is the daily river flow and the corresponding flow duration curve for each hydropower plant location (HPP1, HPP2 and HPP3). In addition, the contribution of rainfall, snow, glaciers, and baseflow to the river flow was quantified.

This glacio-hydrological assessment delivered river flow estimates for three intake locations of hydropower plants in Nakra, Georgia. The assessment included the calibration of a hydrological model, daily river discharge simulation for an extended period of record (1980-2015), and the derived flow duration curves and statistics to evaluate the flow operation of hydropower turbines. The daily flow calculations for the three sites (HPP1, HPP2 and HPP3) can be used in the hydropower calculations, and to assess the overall profitability of the planned investment, considering energy prices, demand, etc.

In the Nakra basin, glacier and snow model parameters were tuned to obtain accurate river flow predictions. Also, the latest technology of remote sensing data on precipitation and temperature (product ERA5) was used to reduce potential errors in flow estimates. Even though these flow estimates are useful for short-medium term evaluations on profitability of the planned investment, climate change pose a challenge for long-term evaluations. Glacier-fed and snow-fed systems, such as the Nakra basin, are driven by a complex combination of temperature and precipitation. Due to future increasing temperature, and changing rainfall patterns, glacier and snow cover dynamics change under climate warming. This can lead to shifts in the flows, like a reduction in lowest flows, and higher discharge peaks when the hydrological system shifts towards a more rainfall-runoff influenced system (Lutz et al. 2016). This can jeopardize the sustainability of the project on the long-term. To provide a better understanding of future river flows, it is recommended to develop a climate change impact assessment.