Modeling Hydrodynamic Changes Induced by Run-of-River Hydropower Plants along the Prahova River in Romania

The purpose of the study is to reveal changes of the hydrodynamics and sediment transport induced into the river channel by the operation of small hydropower plants (SHPs). A 36-km reach of the upper Prahova River in Romania has been chosen, along which 10 run-of-river developments are built. A 1D modeling software was used to compute hydrodynamic parameters over the selected reach. Two discharge scenarios were considered into the channel: (1)mean annual flow (for the natural regime, without SHPs), and (2)the minimum discharge (worst case scenario of SHP operation for the environment). Results of the second scenario show that ecologically relevant hydraulic parameters in the channel are approaching the thresholds of endangering the fish habitat. On average, depth and shear stress drop by 50%, mean velocity by 40%, and flow area by 75%. Comparison between computed nondimensional shear stress and its corresponding critical value indicates that minimum discharge can only transport finer particles than average from the bed surface, thus leading to potential filling of fish spawning areas with sand.