Key Concepts
Power developed from movement of water.
History of waterpower
Humans have employed the power of flowing water (Fig. 1) for thousands of years. Initially, waterpower was utilized as a means to power various types of mills and other mechanical processes. In the late 1800s, the first hydroelectric plant in the United States began operation on the Fox River in Wisconsin. In the early 1900s and continuing through the middle of the twentieth century, many dams were converted or constructed to produce electricity for the population’s growing energy needs. Though development of waterpower resources has slowed in the twenty-first century, there is potential for growth; only a minimal number of the United States’ 90,000 dams (as documented by the U.S. Army Corps of Engineers National Inventory of Dams) currently have power-generating capabilities. See also: Dam
Hydropower
Hydroelectric power relies on the flow of water to turn a mechanical turbine, which spins an electric generator, producing electricity. This process is shown in Fig. 2: Water enters a project’s intake and flows through a pipe structure, called a penstock, that conveys water from the reservoir to the powerhouse that contains the generating equipment. A transformer increases the voltage of the generated electricity, such that it can be sent to the electrical grid via transmission lines. Water used to spin the turbine is then released back to the waterway via a draft tube. This represents a conventional impoundment, or reservoir-type, hydropower facility. There are several different types of operating regimes that utilize this same generation process. See also: Electric power generation; Hydroelectric generator; Reservoir; Transformer; Transmission lines; Turbine
Operating regimes
Impoundment/reservoir
Water is stored in a reservoir by a dam, and the water is released to provide generation flow in response to electric-grid demands.
Diversion
Water is channeled from a waterway via a canal or penstock into a powerhouse, which discharges flows back into the waterway.
Run-of-river
Water outflow from a hydropower facility is approximately matched with inflow from the waterway at all times. This mode can either include a dam or a diversion structure. With little variation in water flow, this operating regime minimizes risk to the ecosystem that the hydropower facility relies on.
Run-of-release
In some cases, water flow from a dam is not controlled by a hydropower project. This often is the case when a dam is owned by a government agency and water is managed primarily for irrigation, drinking water, or flood control, but the hydropower facility is separately owned. This operating regime is similar to run-of-river; but rather than matching river inflow, this mode matches inflow of releases from a dam, as allowed by the owner, with outflow from the hydropower project.
Peaking
An impoundment or reservoir project stores water until a time when electricity demand is at its peak. At this point, water is released through the turbine to generate power to match peak-load demand for electricity in a region.
Conduit
A conduit is a form of diversion project that utilizes a penstock or pipe to channel water flow from an existing water supply, wastewater, or irrigation system to generate power. This type of project does not connect directly to a natural waterway.
Pumped-storage hydropower
In pumped-storage hydropower, battery-like technology utilizes two reservoirs (Fig. 3). Water is stored in an upper reservoir until electricity demand peaks (generally on weekdays and in the early evening). Water is released from the upper reservoir, generating electricity to support high demand, and is then stored in the lower reservoir. When electricity demand and prices are low (generally at night and on weekends), the turbines are reversed, pumping water from the lower reservoir into the upper reservoir. These systems use more energy to pump water into the upper reservoir than they produce, but pumped storage helps mitigate peak electricity demand and supports the integration of intermittent generating technologies, like wind and solar. See also: Pumped storage; Solar energy; Wind power
Marine hydrokinetics
Marine hydrokinetics, a burgeoning waterpower field, utilizes wave, tidal, and other marine forms of energy to generate power. Though there are only a few of these projects currently in operation, they represent an opportunity to generate clean electricity using the power of the ocean and tides. See also: Tidal power
Oversight and licensing
In the United States, the Federal Energy Regulatory Commission is the government agency responsible for the oversight and licensing of waterpower projects. The commission issues licenses for the construction and operations of most new waterpower projects and for the continued operation of existing projects (also known as relicensing). It also oversees ongoing project operations, dam safety inspections, and environmental monitoring. The licensing process includes input from state and federal resource agencies, tribes, and stakeholder organizations, as well as studies of the potential socio-environmental impacts of project operations. Through this process, stakeholders convene to ensure the needs of the surrounding communities are considered alongside power generation potential.
Value
Aside from power generation, waterpower provides various other services to the electrical grid and to society. Waterpower is a domestic resource that forgoes reliance on international fossil-fuel sources. It relies on the water cycle, a process driven by the Sun, making it a renewable resource. Additionally, waterpower is flexible. These facilities can be quickly brought online to provide generation during periods of high demand or to support energy needs in a blackout. Waterpower can provide baseload power, the minimum amount of power needed at any given time, which supports the integration of intermittent renewable energy sources, such as wind and solar power. When the Sun does not shine or the wind does not blow, waterpower can be relied on to maintain grid reliability without having to turn to nonrenewable forms of fuel. See also: Electric power systems; Energy source; Hydrology; Water resource
Outside of the power grid, waterpower plays other important roles in our society. Waterpower reservoirs are used to supply drinking and irrigation water, as well as for flood control and recreation. Waterpower operators often work in tandem with state and federal resource agencies to plan for impending flood conditions and are able to mitigate risk to surrounding communities by providing storage of otherwise dangerous amounts of water. Storage in reservoirs also supports water supply needs for surrounding communities. Similarly, waterpower projects situated in irrigation districts can be utilized as reservoirs for storage of irrigation waters. Power can be generated, and irrigation needs can be met. Reservoirs are also used for recreational opportunities, and most waterpower projects are required to provide safe access for swimming, boating, and fishing. Their flows can also support white water boating opportunities. Projects often provide portage for canoes and kayaks to bypass a dam or waterpower project.
Considerations
The construction and operation of waterpower projects may also have socio-environmental effects on surrounding communities. These can be classified into three categories: water-quality effects, wildlife impacts, and social implications.
Water-quality effects
Waterpower projects, especially their construction, can impact the water quality of a body of water. Issues include low dissolved oxygen concentrations, siltation and sedimentation, varying water temperature, and nutrient loading. For river systems, instream flows must also be considered. A waterpower project can dewater downstream reaches of a river, impacting aquatic resources and their habitat unless a minimum flow is provided. See also: Freshwater ecosystem; River; Stream transport and deposition
Wildlife impacts
In riverine ecosystems, dams often span an entire river, creating a barrier that might fragment habitat and disrupt natural passage routes for fish and wildlife. To complete their life cycles, many fish must travel from freshwater to the ocean or vice versa. Fish that begin their life cycle in freshwater, migrate as juveniles to the ocean, and return to freshwater to spawn are known as anadromous species. Catadromous species begin their life cycle in salt water, migrate to freshwater, and finish their life cycle in salt water. Not all fish species require these migration patterns to complete their life cycle and are thus unaffected by built barriers. Other water-dependent wildlife can be disrupted by facility infrastructure or operations. See also: Fisheries ecology
Habitat
As mentioned earlier, waterpower projects have the potential to alter natural flow regimes and the water quality of a body of water. Impacts on these parameters may have detrimental effects on aquatic biota residing in a body of water.
Shoreline impacts
Altered flow regimes may erode shorelines, causing increased sediment in a body of water. This is a water quality concern and also impacts available terrestrial habitat along shorelines that may have been flooded when the dam was built. See also: Depositional systems and environments; Fluvial sediment
Social implications
Cultural resources
Cultural resources include material remains of past and present human life of significant cultural or archaeological interest. These resources provide scientific or anthropological understanding of past behavior and cultural adaptation. When a waterpower project applies for an operating license, all cultural or historic resources must be identified and plans for their preservation and mitigation must be developed. Otherwise, construction activities, operations, and changes in water levels or river flows might adversely impact these important resources. See also: Anthropology; Archeology
The creation of hydropower reservoirs, especially in the early 1900s, resulted in losses of access to traditional fishing grounds and areas important to indigenous peoples. These historical impacts and contemporary impacts to indigenous cultures must also be considered.
Recreation
Waterpower projects present a unique opportunity to provide safe access for recreation in and around bodies of water; however, their presence might also hinder these opportunities. Implementation of new flow regimes can impact available boating access, shoreline degradation can impact campsites or trails, and habitat fragmentation might cause a decline in fishery or wildlife resources. These considerations are all assessed during licensing and must be balanced based on recreation needs.
