Hydropower schemes can broadly be classified into four main types: (check)

           1.  Run-of-river
         The process of using water supply directly from a river with no significant strive to store water or control flow; (of a hydroelectric power plant) making                 use of such a water supply; of or relating to such a water supply or power plant.

            2.  Storage hydro
           Hydropower projects with a reservoir can store water for later use, typically by preserving  water during the high-flow season (spring, rainy season) and             releasing water during the low-flow season (winter, dry season). A reservoir gives a higher flexibility and allows the hydropower plant to adapt                               enhanced to the demand profile, both in the short term (hours, days) and seasonally.

            3. Pumped storage

            A pumped storage hydropower scheme consists of a reversible power plant and two reservoirs, connected by a pipe or a tunnel. The major purpose is                to store energy by pumping water up into the better reservoir during low-demand periods and generate (peaking) power by releasing the water back                  to the turbine during high-demand periods.

            4.  Hydrokinetic

           This equipment is less developed and less used than the other three but offers the promise to expand the range of possible sites for hydropower                          development to rivers and canals where it can harness energy straight from flowing water, rather than from a hydraulic  head formed by dams or other              control structures.

             5.  Underground power plants
            A very good example of facilities where the underground space is used to convey water are underground hydropower stations.

           An underground power station is a type of hydroelectric power station constructed by excavating the major components (e.g. machine hall, penstocks,              and tailrace) from rock, rather than the more ordinary surface-based construction methods. Often underground power stations form part of pumped                storage hydroelectricity schemes.

          Their crucial function is to level load. They use low-priced or surplus off-peak power to pump water from a lower lake to an upper lake. Then, during                    peak periods (when electricity prices are often high), the power station generates power from the water held in the upper lake.

               6. Large and small hydro

                         It has become popular to categorize hydropower plants either as “small” or “large,” depending on installed capacity. There appear to be a belief                             that “small is beautiful” and that small hydro are more environmental friendly. In some countries, small hydro schemes are accepted for                                        development and receive subsidies while larger hydro schemes are not subsidized.

                  If one looks at the impact per kilowatt hour, the picture becomes more complicated, and one large hydropower plant could easily have less impact                      (per kilowatt hour) than many small plants of the same capacity united.