As the need for energy is increasing, the challenges in the future are to operate existing large hydraulic schemes in more sustainable ways and to develop future water resources projects that are able to achieve a better balance between environmental and socio-economic demands. In this context, scenarios combining different levels of environmental requirements as well as hydropower developments were simulated at a daily time step with a hydraulic-hydrological model (the Soil and Water Assessment Tool) over the Zambezi River Basin. For each scenario, the hydropower operation rules, the mean annual energy produced and the firm powers were considered. The impact on the flow regime was characterized by a hydrological alteration indicator and Pard, coefficients. In the present state, the total mean annual energy production is about 30,000 GWh with a firm power of about 3,000 MW. The impact of the dams on the flow regime is low in the Kafue flats and the Zambezi delta and high in the Mana Pools. The new run-of-river hydropower plants aim to increase the mean energy production by more than 90 % and the firm power by about 40 %. Releasing e-flows can reduce the impact in the Kafue flats and in the Zambezi delta, with a loss of less than 10 % of mean annual energy production and about 15 % of the firm power at Itezhi-Tezhi and Cahora Bassa. This reveals that a compromise between energy production and environmental sustainability can be reached.