Changes in Hydrologic Regime to Balance Human and Environmental Requirements: a Case Study in the Långan River Basin, Sweden

Abstract: Dams and reservoirs play an important role in the Swedish energy system, and a large number of rivers are today regulated. How to combine the ecological and economic interests in the regulation of these rivers is a growing concern for stakeholders and authorities. The aim of this study was to develop a conceptual environmentally- oriented dam release plan that combines economic and ecological needs for the Lower Långan Natura 2000 area as well as evaluating how the water stage of the reservoir Lake Landösjön would change with a more environmentally oriented flow regime. Three flow scenarios were established: (0) Current flow regime, (1) EU demand for good ecological status which requires changes in discharge dynamics, and (2) the environmental design flow. The Dundee hydrological regime assessment method (DHRAM) was used to evaluate the hydrological alterations for each of the three scenarios. Scenario 0 exhibited the largest alteration from natural flow and the results from the DHRAM analysis indicated on high risk of ecological impact in the river system. Scenario 1 met EU’s demand of good ecological status but the water stage in Lake Landösjön exceeded the maximum allowed legal limit. Scenario 2 comprised a flow regime encompassing both economic and ecological interests and is the most realistic scenario for improving ecology in the Lower Långan River. In conclusion in order to meet EU demand of good ecological status a change in upstream regulation is needed.