Small hydro
Small hydro is the development of hydroelectric power on a scale suitable for local community and industry, or to contribute to distributed generation in a regional electricity grid.
[7] An additional defining feature of small hydro is known as run-of-river, or that the physical impact of the project is relatively minuscule compared to major hydroelectric dams which require a water storage lake.
The solution to coping with increased demand was to offer contracts to independent power producers, who have built 100 run of the river projects under 50 MW.
However, as the need for power generation increased small hydropower projects were phased out in favor of the large scale dams using newly designed turbines.
[16] Post 20th century environmental doctrine is moving away from large-scale hydropower construction due to the increased awareness of ecological problems associated with dams.
For instance, the large artificial lakes often flood habitats and communities and disrupt species reliant on consistent river flow.
Small hydro may be developed by constructing new facilities or through re-development of existing dams whose primary purpose is flood control, or irrigation.
Small "run of the river" projects do not have a conventional dam with a reservoir, only a weir to form a headpond for diversion of inlet water to the turbine.
Unused water simply flows over the weir and the headpond may only be capable of a single day's storage, not enough for dry summers or frozen winters when generation may come to a halt.
[18] "Irrigation districts across the U.S. have installed power plants at diversion points and in-canal drops, which are traditionally used for flow measurement, to stabilize upstream heads and to dissipate energy where there is significant elevation change throughout the canal system.
The physically smaller size of equipment makes it easier to transport to remote areas without good road or rail access.
[20] The primary advantages of small hydro development include low cost to build, environmental justice, and ability to remain disconnected from centralized power grids.
For instance, rural areas in India or other countries that have flowing water regimes utilize small hydro to provide a renewable source of energy without connection to the national grid.
[21] Additionally, in communities which are geographically isolated from national power grids small hydro projects provide the greatest reduction in green house gas emissions.
[23] A final noted advantage of small hydro over larger hydropower developments or fossil fuel plants is an element of environmental justice.
Within run-of-river design projects, the greatest harm for water systems are flow regime alteration, loss of river cohesion and connectivity, and habitat degradation effecting fish and macroinvertebrates primarily.
