What are the environmental impacts of damming rivers?

1 Alteration of flow

One of the most obvious impacts of damming rivers is the alteration of the natural flow regime, which is the pattern and variability of water discharge over time. The flow regime influences many ecological processes, such as nutrient cycling, sediment transport, habitat formation, and migration patterns. Damming rivers reduces the flow variability, disrupts the seasonal cues, and creates artificial reservoirs that alter the temperature, oxygen, and chemistry of the water. These changes can have negative consequences for the aquatic organisms and plants that depend on the natural flow regime for their survival and reproduction.

2 Fragmentation of habitats

Another major impact of damming rivers is the fragmentation of habitats, which is the division of continuous natural areas into smaller and isolated patches. Habitat fragmentation reduces the connectivity and diversity of the river ecosystems, and affects the movement and distribution of species. For example, dams can block the migration routes of fish that need to access different habitats for spawning, feeding, or escaping predators. This can reduce their genetic diversity, population size, and resilience. Moreover, habitat fragmentation can increase the exposure of native species to invasive species, diseases, and predators that can thrive in the altered conditions.

3 Sedimentation and erosion

A third important impact of damming rivers is the sedimentation and erosion that result from the interruption of the natural sediment balance. Sediment is the solid material that is carried by the water and deposited on the river bed or banks. Sediment plays a vital role in shaping the river morphology, providing nutrients and habitats, and buffering pollutants. Damming rivers reduces the sediment load downstream, which can cause erosion of the river bed and banks, loss of habitats, and degradation of water quality. On the other hand, damming rivers increases the sediment accumulation upstream, which can reduce the storage capacity of the reservoirs, increase the risk of landslides, and affect the aquatic life.

4 Greenhouse gas emissions

A fourth significant impact of damming rivers is the greenhouse gas emissions that are associated with the construction and operation of dams and reservoirs. Greenhouse gases are the gases that trap heat in the atmosphere and contribute to global warming and climate change. The main sources of greenhouse gas emissions from dams and reservoirs are the carbon dioxide and methane that are released from the decomposition of organic matter in the flooded areas, the combustion of fossil fuels for the construction and maintenance of the infrastructure, and the leakage of water from the turbines and pipes. The amount and type of greenhouse gas emissions depend on various factors, such as the size, location, age, and design of the dams and reservoirs.

5 Social and cultural impacts

A fifth and final impact of damming rivers is the social and cultural impacts that affect the human communities that live near or depend on the rivers. Damming rivers can have positive effects, such as providing jobs, income, and services, but it can also have negative effects, such as displacing people, disrupting livelihoods, and affecting health and well-being. Moreover, damming rivers can affect the cultural and spiritual values that people attach to the rivers, such as their identity, history, and traditions. These impacts can vary depending on the context, scale, and participation of the affected communities.

6 Here’s what else to consider

This is a space to share examples, stories, or insights that don’t fit into any of the previous sections. What else would you like to add?