How Dams Affect River Health

Dams change the environmental conditions in a river health, altering pressure, temperature, oxygen levels and dissolved chemical and physical properties. This impacts the species and their habitats that live in a river.

Fish species whose migration is blocked by dams are not able to reproduce and decline in population. This can have a negative impact on other species in the food chain and ecosystem.

Water Levels

The water levels at dams affect the health of rivers. Unless engineered to allow fish to pass through them, they can block habitat for fish that need to migrate up and down streams to spawn.

This reduces the chances of migratory salmon, for example, completing their round trip to reach their upstream spawning sites. They may die while trying to make the journey, and their populations decline as a result.

Dams also trap sediment, burying rock riverbeds where fish can lay their eggs and grow. This makes it harder to create and maintain more complex in-stream habitat.

Dams release oxygen-deprived water with unnatural temperatures into the river below, threatening downstream ecosystems as well. This can lead to algal blooms and reduced oxygen levels, affecting river wildlife.

How Dams Affect River Health Water Temperature

Water temperatures can have a big impact on dam health. Scientists used satellite data to look at how several hydropower dams affected the temperature of three major rivers that flow into the Mekong River in Southeast Asia.

The study found that within a year of the dams coming online, downstream river temperatures dropped by up to 3.6 degrees F (2 degrees C). That cooling lasted for several months.

Thermal pollution, or changes to the normal water temperature regimes, can have profound effects on freshwater ecosystems (Langford, 1990). These alterations can range from industrial cooling activities to discharges of cold water into streams below large impoundments (Baxter, 1977; Ward and Stanford, 1979; Ward, 1985).

When the temperature of the surface water drops, it can decrease the rate of chemical and biological reactions in the water. This can also affect the number of oxygen-requiring organisms in the water.

How Dams Affect River Health Water Flow

Water flows at dams play a key role in the overall health of the river system. They help to control the amount of water flowing through rivers and also provide a source of drinking water to those who live in close proximity to the dam.

Flows at dams can be measured in various units such as cfs, cms, gpm, millions of gallons per day (MGD) and others. Understanding flow is crucial for design, operations and billing purposes.

Flows at dams can also change dramatically over time, which is why it is important to monitor them closely. This is especially true for large reservoirs.

Water Quality

Dams can impact water quality by altering chemical and physical processes that affect water. These effects may include changes in temperature, oxygen, and dissolved nutrients.

Dam operation can also affect water quality by slowing flow and trapping sediments that may interfere with biological activity. These impacts can lead to reduced dissolved oxygen levels in streams and decreased fish survival.

The health of dams is determined by a number of factors, including the type and amount of water in the reservoir, the location of the dam, the surrounding land use, and seasonal weather conditions. The chemical factors that influence water quality include dissolved major ions, dissolved nutrients, dissolved organic matter, dissolved gases (oxygen and carbon dioxide), and trace metals.

Water quality is important to dam owners and their communities. The quality of water affects the ability of people to drink, industrial uses, and the ecosystems in which they live.