Hydraulic criteria and estimation of the hydropower plant (HPP) operation impact on the river environment

Abstract

Interaction between a river and its environment is crucial, and negative impact of a HPP operation on the environment must be estimated. In order to be able to evaluate this impact, hydraulic parameters such as velocity, water depth, Froude Number (Fr) and fluctuation of flow regimes have been measured and hydro biological indices of water quality (HBI) have been calculated. Field experiment on the consequences of HPP turbines’ operation in the rivers Virvyte and the Susve has been performed in natural, directly and indirectly impacted regimes in 10 cross-sections. To predict the influence of HPP, the meaning of Fr number criterion and the number of hydrophytes are compared. The results show that even small dams and reservoirs of HPP may impact the environmental change through facility operations over a sustained period, because in pounded reaches nearby/above HPP dams in the River Virvyte low Fr number in habitats (0.04>Fr> 0.0007) has been established. In the River Susve, below the Angiriai HPP, a serious disturbance of hydraulic parameters is determined when a positive wave front resulting from an increase of initial sanitary flow rate Qs =0.4m3 /s to total flow rate Qtot =10.4 m3 /s is moving downstream after the switching on the turbines. The maximal water level increase speed Δh /Δt( 0.18 m/min=10.8 m/h) is recorded on the second minute from start of the turbine. Consequently, it creates additional pressure of about 200kPa at the instant and can be a strong stressor for biological community of the river. Over 1 km long propagation of the surge without loosing much potential energy (because it is perpetual) is the main reason to avoid rapid operation of HPP turbines in practice.