Hydroelectric dams are considered a highly reliable source of electricity and as a result are used in many countries across the globe. However, there are some significant environmental impacts of hydroelectric dams that can have severe consequences for the biological, chemical and physical properties of rivers and their surrounding landscapes.
It’s important to understand that many of the environmental impacts associated with hydroelectricity relate to the damming of a river. As a result of this, we need to consider that if a hydroelectric facility has multiple uses (such as providing a source of water for a town or city) then the environmental impacts should be shared across each use and not entirely associated with hydroelectric power generation but rather the dam itself.
The environmental impacts of hydroelectric dams vary greatly depending on the size and location of the facility and therefore assessment of the impacts should be carried out on a case-by-case basis. Below, we will take an in-depth look into the generic impacts of hydroelectric dams.
Impacts on Wildlife
When a hydroelectric dam is constructed, a reservoir is created that floods a large area. The scale of the flooding can vary greatly and has the potential to displace wildlife, destroying habitats in its process.
When a hydroelectric dam alters the flow rate of a river and a reservoir is created, this results in a stagnant body of water that can have a significant depth in places. Over time, this stagnant water becomes higher in sediments and nutrients which paves the way for increased levels of algae and other aquatic weeds and can lead to the crowding out of other river animal and plant life.
It has been known for fish to enter the water intakes of hydroelectric dams, resulting in their death when they come into contact with a turbine. To mitigate this, some companies are now looking into the feasibility of installing fish-friendly turbines that minimise the risk to a fish as it passes through a turbine.
Hydroelectric dams can also have an impact on the migratory path of certain fish species such as salmon and trout. These particular species of fish are known to travel upstream to spawn and the presence of a dam makes this an impossible task resulting in falling populations. Some dams mitigate this by installing “fish ladders” that provide an alternate, more natural route for the fish to continue on their journey.
Impacts on Wildlife Further Downstream
The formation of a dam can also have severe impacts on habitats downstream. When the natural flow of a river is blocked so is that of the sediments and nutrients contained within the water. These sediments and nutrients are often vital for replenishing downstream ecosystems such as wetlands, flood plains and deltas. This in itself can lead to the disappearance of birds and other species.
The stagnant reservoir of a hydroelectric dam is often much colder and lower in dissolved oxygen levels. As this water is released through a hydroelectric dam it can alter the temperature and oxygen levels of the water further downstream resulting in dangerous conditions for fish and other river habitants. Some hydroelectric dams are able to mitigate these impacts by installing aerating turbines that increase the oxygen levels before been released downstream and by installing multi-level water intakes that extract water from various levels of the reservoir and not just the bottom (where the water will be at its coldest.)
As water is held back by a dam, the water table can gradually reduce further downstream. This can have disastrous consequences for plants, shrubs and trees as their roots struggle to absorb enough nutrients.
Impacts on Rivers
When a rivers flow is altered this can have various impacts on a river. Erosion is often seen both upstream and downstream after the construction of a hydroelectric dam due to changing river levels and intensity. This has been known to have implications for man-made structures such as roads and bridges.
Sections of river downstream from a hydroelectric dam have the potential to dry out if the flow of water is not management sufficiently. In some countries, hydroelectric power companies are obliged to release set levels of water over the course of the year to mitigate the problem. This careful management can have positive results and a lesser impact for habitats and communities further downstream.
Impacts on Land
The obvious issue when it comes to the impacts that hydroelectric dams have on the land is down to the area of land that needs to be flooded in the first place. This process destroys habitats and can result in entire communities having to relocate.
Further downstream, there can be sever impacts for agricultural land where farmers may have relied on the fertile soils close to rivers. This can result in farmers having to increase their use of pesticides which can be harmful to both land and rivers.
There are numerous atmospheric impacts associated with hydroelectric dams. A key impact relates to the flooding of land that can be home to significant levels of vegetation. As this vegetation is submerged, it begins to decay which results in a build up and release of methane which is one of the most potent greenhouse gases.
Rivers are known to drive sediments and nutrients deep into the ocean. These sediments and nutrients can aid the production of algae and other aquatic weeds which are known to absorb carbon dioxide from our atmosphere. If a river has been dammed then the flow of sediments and nutrients isn’t as great as it would have been in the past resulting in less carbon dioxide been absorbed by algae out at sea.
Solutions To The Impacts
As previously mentioned, several of the impacts that hydroelectric dams have on the environment can be mitigated with the help of various solutions. Fish ladders can aid salmon and trout in their migratory paths whereas innovations in engineering can help to maintain the right temperature and oxygen levels of water that is released downstream. All this coupled with careful management of how much water is released downstream can have highly positive results.