  Hydropower is a renewable, controllable, and flexible source of electricity.
These are instrumental features to support decarbonization efforts, as an
enabler of non-controllable and variable sources of renewable electricity.
Sometimes hydropower is accompanied by other services provided by multipurpose
reservoirs, such as water supply, irrigation, navigation, flood control and
recreation. Despite all these benefits, hydropower can be a polarizing issue. A
large sample of projects with poor planning and execution provides numerous
arguments for its opponents. Large and complex projects frequently suffer
overcost and delays. The direct impacts are related to the disruption of river
ecosystems and surrounding habitats due to the flooding of large areas, and the
fragmentation of rivers caused by the construction of dams and the reduction of
sediment transport that impoverishes aquatic life. People displacement and
compensation are always a complex issue. Hydropower projects can also cause
indirect impacts, such as additional deforestation related to the construction
of workers' villages, access roads and transmission lines. Finally, reservoirs
may also become a significant source of methane emission, especially in
tropical areas. This paper offers an analytical approach for sustainable
hydropower planning at the river basin scale called HERA: Hydropower and
Environmental Resource Assessment. Built on three main components, namely
geoprocessing, engineering, and optimization, HERA screens and compares
hydropower development alternatives to guarantee social and environmental
objectives while maximizing mentioned economic benefits. It was designed to
encourage a transparent and participatory hydropower planning process from the
early stages. Experience has shown this approach increases the chances of
better and balanced outcomes. A case study is presented in the Ogooue river
basin in Gabon.
