What Are The Disadvantages Of A Hydroelectric Generator?

Environmental Impacts

Hydroelectric dams can have significant environmental impacts by disrupting river ecosystems and fish migration routes.[1] The flooding of land to create a reservoir destroys forests, wildlife habitats, and agricultural lands upstream of the dam.[2] This drastically alters the natural flow of the river and the transportation of nutrients, as well as prevents the downstream movement of organisms and sediments.[3]

hydroelectric dams can disrupt fish migration routes and prevent access to spawning grounds

Dams disrupt the deposition of silt, which normally nourishes downstream floodplains and ecosystems. This can allow for excessive erosion below the dam and the gradual disappearance of river deltas.[3] Reservoirs themselves often emit greenhouse gases as vegetation decomposes underwater.[1] Overall, dams fragment continuity in the river which can threaten the survival of fish stocks and other aquatic life. Fish passage facilities built into dams have met with varying degrees of success.[2]

Social Impacts

The construction of hydroelectric dams often leads to the displacement of local communities that previously lived in the area. The creation of reservoir lakes behind the dams can flood villages, agricultural land, and sacred indigenous sites. This displacement severs peoples’ connection to their ancestral homelands and can erode local culture and community ties.

For example, the construction of the Akosombo Dam for the Volta River Project in Ghana displaced over 80,000 people from their communities. This disrupted local social organization and agricultural production (Cernea 2004).

Hydro dams also frequently impact local economies and livelihoods built around fishing, agriculture and river-based transport. The dams can restrict access to the rivers, alter flow regimes, and degrade water quality – all factors that can cripple local industries. In many cases, promised job creation and economic stimulus from the dams fails to materialize.

Additionally, the loss of cultural heritage sites to inundation by the reservoir lakes represents an irreversible destruction of history. Important archaeological, sacred and historical sites can be erased. For example, construction of the Chixoy Dam in Guatemala destroyed many Maya ruins and artifacts (Bigda-Peyton 2011).

Geological Impacts

Hydropower dams and reservoirs can have significant geological impacts, including increased seismicity and landslides due to water impoundment as well as changes to groundwater levels downstream. According to the U.S. Geological Survey, the weight of the water in a reservoir can cause small earthquakes by increasing seismic stresses or lubricating existing faults in bedrock below. These seismic events tend to be low on the Richter scale but can damage infrastructure over time. Landslides may also occur on slopes near new reservoirs as soil saturation increases (https://www.usgs.gov/special-topics/water-science-school/science/hydroelectric-power-water-use).

Reservoirs also alter natural groundwater recharge patterns downstream, causing the water table to fall and decrease discharge. Lower groundwater levels can have ecological consequences by reducing soil moisture and affecting riparian vegetation and aquatic species. One study found groundwater depletion up to 6 km downstream from a reservoir in Zimbabwe (https://www.ucsusa.org/resources/environmental-impacts-hydroelectric-power). Careful reservoir operation and allowing environmental flows can help mitigate geological impacts on groundwater.

Financial Costs

Hydroelectric power plants require very high upfront infrastructure costs. Building a new hydroelectric dam and power plant can cost anywhere from $1,000-$5,000 per kilowatt of power generation capacity, with costs varying greatly depending on the size of the project and site-specific factors.

According to the U.S. Department of Energy, hydroelectric power has the highest average construction costs of any power generation technology in the United States, with costs averaging around $2,500 per kilowatt of capacity. In comparison, natural gas power plants cost around $1,000 per kilowatt, while wind and solar power both have average construction costs below $2,000 per kilowatt.

In addition to the huge initial investment, hydroelectric plants also require significant ongoing operation and maintenance costs. Dam and reservoir maintenance, equipment repairs, licensing fees, and personnel salaries all add up. According to the International Energy Agency, annual operating costs for large hydroelectric facilities generally range from 1-4% of initial infrastructure costs.

While hydroelectricity itself has minimal fuel costs, the high construction and maintenance costs required over the project lifespan result in hydroelectric power generally having a higher total lifetime cost compared to other renewable energy sources like wind and solar power.

Limited Locations

Hydroelectric power is only suitable in certain geographic areas that meet the right conditions. Generating hydroelectricity requires sufficient water flow and elevation drop to power turbines. As a result, hydroelectric dams are most commonly found in mountainous regions, gorges, and areas with high annual rainfall. In the United States, most hydropower facilities are located in the West, especially in regions like the Pacific Northwest and California which have ideal terrain and abundant precipitation (EIA).

Because viable sites for hydroelectric dams are geographically limited, there can be competition over desirable locations with sufficient head height and water flow. The best remaining undeveloped sites are dwindling in many parts of the world, making it more challenging to identify appropriate places to build new hydroelectric plants. This geographic limitation restricts how much hydropower capacity can continue to expand globally.

Drought Sensitivity

A major disadvantage of hydroelectric power is its sensitivity to drought conditions. Hydroelectric dams rely on sufficient water flow to turn the turbines and generate electricity. During droughts, water levels can drop dramatically which reduces the output of hydroelectric facilities.

According to the U.S. Drought Portal, as of February 2022, 61% of global hydropower dams are located in river basins facing high or extreme drought risk by 2050 [1]. Droughts threaten the viability of existing hydropower infrastructure. For example, during the California drought from 2012-2016, hydropower generation in the state decreased by almost half [2].

This variability and unreliability in energy output makes hydropower potentially risky for communities that depend on it. Droughts are expected to intensify with climate change, further exacerbating this vulnerability of hydroelectric generation. Solutions like improving reservoir storage capacity can help mitigate drought risks but may be costly and still limited in effect.


Siltation refers to the accumulation of sediments like sand, silt, and clay in the reservoir behind a dam over time. This gradually reduces the storage capacity of the reservoir. According to Dams With Significant Siltation Problems – HydroCoop, sediment coarser than 0.1 mm can accelerate erosion of turbine parts, and even smaller sediment grains can cause damage if they contain quartz.

As the reservoir fills with sediment, less water is available for hydropower generation. Periodic dredging of the reservoir is required to remove built-up sediment. One estimate is that storage capacity is reduced by 1% per year in many reservoirs due to siltation (Dealing with Sediment: Effects on Dams and Hydropower Generation, Hydro Review). Overall, siltation reduces the operational lifetime of the reservoir if not managed properly.

Methane Emissions

One of the major disadvantages of hydroelectric dams is that they produce significant methane emissions. As vegetation and organic material decays in the oxygen-deficient environment of a reservoir, it undergoes anaerobic decomposition and releases methane gas. Methane is a potent greenhouse gas, with more than 25 times the global warming potential of carbon dioxide over a 100-year period (URL). Reservoirs created by hydroelectric dams have been found to produce more methane than natural lakes and rivers. In some cases, hydropower reservoirs emit up to twice as much methane as natural water bodies (URL). Though hydropower is often considered a clean, renewable energy source, methane emissions can make some hydroelectric projects substantial contributors to climate change. Methane emissions vary based on the climate, vegetation, and depth of the reservoirs, but may offset much of the climate benefit of zero-emissions hydroelectricity generation.

Barriers to Fish

One of the main disadvantages of hydroelectric dams is that they often block fish migration routes and access to spawning grounds (https://www.fisheries.noaa.gov/insight/barriers-fish-migration). Dams act as physical barriers that prevent many fish species such as salmon and steelhead trout from reaching their native spawning habitats.

Fish ladders and elevators are sometimes installed to help migratory fish bypass dams. However, these passageways are often only partially effective, and many fish are unable to locate the entrances or successfully navigate them. Even dams with fish passage facilities can hinder access to historical spawning sites and disrupt natural migration patterns.

Overall, hydroelectric dams significantly obstruct and fragment waterways that are critical migration corridors and habitat for fish populations. Their presence has contributed to declines in many commercially valuable fish species that rely on river connectivity for their lifecycles.

Downstream Impacts

Hydroelectric dams can significantly impact the environment downstream by altering natural water flows and harming aquatic wildlife. According to a 2021 study in Ecological Applications (Baird et al. 2021), hydroregulations from dams can increase riverbed scouring and erosion, leading to more sedimentation downstream. Dams change the timing and volume of river flows, often resulting in low minimum flows inadequate to support ecosystems. Rapid hourly fluctuations in flows below hydropower dams negatively impact the survival of aquatic organisms. Dams also trap sediments and nutrients within reservoirs that earlier flowed down rivers to replenish wetlands and deltas.

In addition, according to The Conversation (“Hydropower dams can harm coastal areas far downstream,” 2019), water released from dams is often depleted of oxygen, harming downstream river health. Discharges from reservoirs are also colder in winter and warmer in summer than natural flows. These changes to water temperature, oxygen levels, and sediment transport have detrimental effects on downstream aquatic ecosystems and human water usage. Overall, the evidence shows hydropower dams substantially alter downstream hydrology and river ecology through changes to water flow patterns, oxygenation, and sediment transport.

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