Water Resources

Electrical energy generated by the movement of water is hydroelectric power. Two classes of hydroelectric power generation include hydropotential energy conversion and hydrokinetic energy conversion. Hydropotential conversion occurs in rivers and tideways and requires storage (impoundment). Hydrokinetic energy conversion converts the energy contained in river currents, tideways or oceans, or coastline wave vertical fluctuations.

Water Technologies

Hydropower is the most common form of clean energy in use today. In the United States, about 2,500 dams provide about 100 GW of hydropower. Of this installed capacity, about 78 GW is conventional hydropower and 22 GW is pumped storage hydropower.

Additional Output from Existing Hydropower Dams

Additional output from conventional hydropower uses a combination of hydrostatic head and flow through turbines to generate electricity. Pumped storage hydropower uses power during periods of low demand to pump water into an elevated reservoir so that it can be released to generate electricity during hours of peak consumption. Federal hydropower sources consist of projects mainly built and operated by three agencies. The U.S. Army Corps of Engineers (USACE) has 75 power plants with 21.5 GW total rated capacity. The U.S. Bureau of Reclamation (Reclamation) has 58 power plants with 15.1 GW of capacity. The Tennessee Valley Authority (TVA) has 30 power plants with 5.2 GW of capacity. In addition to the federally owned power plants, another 90 nonfederal power plants are located at USACE dams, providing an additional 2.3 GW of capacity, and more than 70 power plants located at Reclamation dams/canals have 0.9 GW of capacity.

The efficiency and capacity of aging turbine units have declined as their physical condition has deteriorated over time. Advances have been made in materials and hydro-mechanical designs, and they could improve the efficiency and performance of turbines and other hydropower system components. Also, many plants in the U.S. hydropower fleet are operating under a different set of constraints than those that existed at the time they were commissioned, which has resulted in reduced energy production and services for the electric power system. Upgrades to the aging equipment would increase power generation.

New Output from Existing Non-hydropower Dams

The United States, which has 2,500 dams that provide 78 GW1 of conventional hydropower and 22 GW of pumped storage hydropower, also has more than 80,000 nonpowered dams (NPDs), which do not produce electricity but do provide a variety of services, ranging from water supply to inland navigation. The monetary costs and environmental impacts of dam construction have already been incurred at NPDs, and adding power to the existing dam structure could be achieved at a lower cost, with less risk, and in a shorter time than would development that required the construction of new dams. The abundance, cost, and environmental favorability of NPDs, combined with the reliability and predictability of hydropower, make NPDs a highly attractive source for expanding the nation’s renewable energy supply.

However, some rivers are not usable for hydropotential energy conversion because surrounding land use or other environmental factors preclude the building of impoundments or because the possible differential in water height between the high and low pool is too small to be able to generate enough power to justify economic development.

New Output from Marine and Hydrokinetic (MHK) Energy Technologies

Marine and hydrokinetic energy is electrical energy from (1) waves: (2) tidal currents in oceans, estuaries, and tidal areas; (3) free-flowing water in rivers, lakes, and streams; or 4) free-flowing water in man-made channels. Although assessments of hydrokinetic energy from river and ocean current resources are currently incomplete, the U.S. Department of Energy (DOE) released two assessments on January 18, 2012, revealing that waves and tidal coastal currents could contribute significantly to U.S. electricity production. The first was released by EPRI (2011) and the second by Georgia Tech Research Corporation (2011). Significant opportunities for wave energy exist along the East Coast and parts of the East Coast have strong tidal currents that could be used to produce energy. The United States uses about 4,000 terawatt hours (TWh) of electricity per year. DOE estimates that the maximum theoretical amount of electricity generation that could be produced from waves and tidal currents is approximately 1,420 TWh per year, which represents about one-third of the nation’s total annual electricity use.


DOI (U.S. Department of the Interior) et al, 2007, Potential Hydroelectric Development at Existing Federal Facilities, for Section 1834 of the Energy Policy Act of 2005.

EIA (Energy Information Administration), 2010, Data from EIA-906, EIA-920, and EIA-923 Databases. http://eia.doe.gov/cneaf/ electricity/page/eia906_920.html.

EPRI, 2011, Mapping and Assessment of the United States Ocean Wave Energy Resource, Technical Report 1024637, Palo Alto, CA, http://www1.eere.energy.gov/water/pdfs/mappingandassessment.pdf. Accessed March 2013.

Georgia Tech Research Corporation, 2011, Assessment of Energy Production Potential from Tidal Streams in the United States: Final Project Report, under Award Number DE-FG36-08GO18174, June, http://www1.eere.energy.gov/water/pdfs/1023527.pdf. Accessed March 2013.

Hall, D.G., S.J. Cherry, K.S. Reeves, R.D. Lee, G.R. Carroll, G.L. Sommers, and K.L. Verdin, 2004, Water Energy Resources of the United States with Emphasis on Low Head/Low Power Resources, U.S. Department of Energy Report DOE/ID-11111.

Reclamation (U.S. Bureau of Reclamation), 2011, Hydropower Resource Assessment at Existing Reclamation Facilities. Denver, Colo. March.

1 1 gigawatt (GW) = 1,000 megawatts (MW). On an annual basis, 1 MW of hydropower produces enough electricity to power nearly 400 U.S. homes. Each GW could power up to 400,000 homes.