Hydroelectricity converts the mechanical energy of moving water into electrical power. This process typically involves constructing a dam or diversion structure to manage the river’s flow and elevation drop. As one of the oldest and largest sources of clean power globally, hydropower contributes approximately 15% of the world’s total electricity supply, involving trade-offs concerning environmental and social impacts.
Generating Reliable and Renewable Energy
Hydroelectric power is recognized as a renewable energy source because it relies on the naturally replenishing water cycle. Unlike power plants that burn fuel, hydroelectric facilities generate electricity without consuming water and produce virtually no atmospheric emissions. This positions hydropower as a low-carbon option, aiding in the reduction of greenhouse gas emissions across power grids.
A defining advantage of reservoir-based hydropower is its operational flexibility, often called “dispatchability.” Operators can quickly start or stop the flow of water through turbines, adjusting power output in seconds or minutes to match fluctuating electricity demand. This rapid response capability makes hydropower an effective tool for stabilizing the grid, especially when integrating intermittent sources like solar and wind power.
The ability of a hydro plant to store energy by holding water behind a dam functions much like a massive battery. Reservoir systems hold an estimated 170 times more energy than the global fleet of pumped storage facilities. This reliable, on-demand power ensures that electricity is available even during periods of low wind or solar production or during major system disturbances.
Financial Investment and Asset Longevity
The economic profile of hydroelectric projects is characterized by a high initial capital expenditure (CapEx) necessary for construction. Building large civil structures, such as the dam, spillways, and powerhouse, requires a significant upfront financial commitment. Costs for large hydropower plants often range from approximately $1,050 to over $7,650 per kilowatt of installed capacity.
This substantial initial investment is balanced by the long operational lifespan of the assets. Many hydroelectric facilities are designed to operate for 50 to 100 years or longer, far exceeding the typical lifespan of most other power generation technologies. Once operational, the ongoing operating and maintenance (O&M) costs are relatively low.
Annual O&M expenses are often estimated to be between 1.5% and 2.5% of the total initial investment costs. This combination of low long-term operational costs and longevity means that the levelized cost of electricity (LCOE) over the project’s life cycle is highly competitive. The initial high cost is amortized over many decades, making the power generation economical in the long run.
Altering Natural Ecosystems
The construction of a dam fundamentally changes a river’s natural flow regime. The formation of a large reservoir upstream transforms a flowing river environment into a still, lake-like habitat. This shift in water characteristics is unsuitable for many native aquatic species that have evolved to thrive in moving water.
Dams create a physical barrier that fragments the river system, blocking the migration routes of species such as salmon and eel. These migratory fish require access to specific upstream areas for spawning, and the blockage leads to habitat isolation and population declines. River fragmentation has been identified as a primary cause for an 81% decline in migratory fish populations since 1970.
The change in the river’s dynamics also affects water quality and sediment transport. Sediment that naturally flows downstream is trapped behind the dam, leading to the erosion of riverbanks and coastal deltas below the structure. Water released from the reservoir can have altered temperatures and lower dissolved oxygen levels, further stressing aquatic life downstream. In some cases, the decomposition of flooded vegetation in the reservoir can generate methane, a potent greenhouse gas, complicating the facility’s overall low-carbon profile.
Implications for Local Communities and Water Use
One severe social consequence of large hydroelectric projects is the forced displacement and relocation of human populations. Flooding a valley to create a reservoir can require moving entire communities, disrupting established social networks and severing generational ties to ancestral land. This displacement, even with compensation, often leads to the impoverishment of those relocated as they lose their traditional sources of livelihood.
Conversely, the construction of dams provides benefits related to water management for communities both upstream and downstream. The large reservoir stores massive volumes of water, providing a stable, regulated source for drinking water and irrigation during dry seasons or periods of drought. This water security is beneficial for agricultural practices in the surrounding regions.
The controlled release of water from the dam allows for effective flood control, protecting downstream communities from seasonal flooding. The ability to regulate river flow mitigates the destructive power of high-water events, offering safety and resilience to populations living in floodplains. While the construction phase can also lead to temporary “boomtown” effects with an influx of workers, the long-term benefits of stable water management are substantial.