Assessment of flow variability and operation efficiency for the Nyagak run of rivers hydropower plant in Zombo district.

Abstract

The Nyagak Run-of-River Hydropower Plant (6.6 MW) in Zombo District depends entirely on natural river inflows, making its generation performance highly sensitive to seasonal variability and climate change. This study develops an integrated continuous hydrological–operational modelling framework to quantify flow variability in the Nyagak catchment (≈590km²) and to assess its influence on daily power production. Continuous simulation using HEC-HMS (Deficit and constant, baseflow recession and Clark Unit Hydrograph as the transform method) was forced with observed station and gridded rainfall/temperature data (baseline 2000–2025), calibrated (2000–2019) and validated (2020–2025). Climate-adjusted inflows were generated using bias-corrected CORDEX-Africa projections under RCP4.5 and RCP8.5. Outputs included a calibrated continuous hydrological model for the Nyagak catchment, daily inflow time-series for baseline and future scenarios, daily power production estimates computed from simulated flows, and scenario comparisons of generation reliability under low- and high-flow conditions.