Development of a new index to assess river regime impacts after dam construction

Construction of dams affects river flow regimes and changes downstream ecosystems in many ways. The impacts of dams depend on local climate, dam purpose and operation policy. This study analysed the impacts of dam construction on river flow regimes and developed a new method to evaluate the effects on river flow. By using three main flow characteristics of river regime (magnitude, timing and intra-annual alteration), a new combined river impact (RI) index to assess construction impacts based on monthly flow data was developed. A preliminary evaluation of the method was made using the river Ebro as a case. A classification was developed where the impact was assessed using a scale from low to drastic. The method was further tested to quantify the effect of dams in 15 rivers located in different regions. The method showed good potential to classify different dam types of variable sizes constructed for different purposes. The RI index method also proved suitable for assessing the environmental impacts of dam construction and could be extended by adding other characteristics of flow regime to evaluate the effects of climate change or changes in land use on river flow regimes.