Very interesting article published in Power Engineering in early June. The main emphasis of the story is that the future of hydro is the non-powered dams (NPDs) with 4-5MW of capacity and located near communities. Kristina Johnson, CEO of Enduring Hydro, makes a point with the untapped capacity at NPDs operated by the U.S. Army Corps of Engineers and believes conversions should be accomplished by executive order. However, these 600 or so dams amount to less than 1% of the total of NPDs. Further, the wave of aging dam infrastructure is a much broader issue beyond the low-hanging fruit discussed in the article, with about 50,000 dams that are >50 years old and many nearing the end of useful life. According to the Dept. of Energy’s NPD report produced by ORNL, there are over 49,000 non-powered, low-head dams that are suitable for hydropower; the average capacity being around 80kW – micro hydro.
http://www.power-eng.com/articles/print/volume-119/issue-6/features/hydropower-s-untapped-potential.html