ASSESSING IMPACTS OF A HYDROPOWER PLANT: EBRO RIVER, SPAIN

Abstract

A small hydropower plant, was built in Navarra province (North Spain), so a small dam was constructed to divert flow from the mainstream to the plant channel. In the reach affected by the flow reduction we studied the impact on the benthic and fish assemblages. Before and after the plant started to operate, different habitat types were sampled by electrofishing and trammel nets to estimate fish populations. Invertebrates were sampled by Neil cylinder in lotic habitats. Densities and biomasses were estimated for invertebrates and fish populations. Besides, growth, condition coefficients and mortalities were estimated for fish. Having compared the flow regime before and after the station began to work, we estimated a considerable loss of aquatic habitat. In consequence, in fast and shallow waters we noticed a dramatic decrease for the biomass of the fish assemblage, although we observed an important increase for density. In different types of habitat where we sampled by nets, we also detected notable decreases in the catch ratio and average weight. We also estimated a remarkable reduction in the density and biomass of the benthic fauna. Results suggest the need of developing latest methods for the impact assessment, studying the natural regime of flow by a set of parameters based on historical data and estimating habitat loss for fish and benthonic assemblages by the Instream Flow Incremental Methodology.