If you're interested in the current state of the US hydropower generation, potential resource out there, and really most everything around hydropower in the USA, check out the NHAAP website.
NHAAP is the National Hydropower Asset Assessment Program, and it's put together a large chunk of the groundwork for the DOE's hydropower vision project.
http://energy.gov/eere/water/new-vision-united-states-hydrop...