Impacts of Site C Dam: Water Loss

When people think of a dam, they usually think of an abundance of water backed up in a reservoir, but water loss is actually another concern with large hydro projects. Evaporation from reservoirs is responsible for over 5-7% of human consumption of fresh water around the world (World Commission on Dams 2001; McCully 2001). Water is lost through ground seepage out the bottom of the reservoir, lack of ice cover downstream (allowing evaporation all year round), and increased surface area of the reservoir. For example, one-third of the Colorado River’s flow gets evaporated from the reservoirs built along the river (McCully 2001).

Other Downstream Effects

Other ways that hydro dams damage downstream areas include the depletion of nutrients and oxygen, changes in water temperature, and abnormal fluctuations in water flow. Nutrient depletion occurs with the build-up of silt behind the dam. This is of particular concern with the Peace River because some of the tributaries within the proposed reservoir carry large amounts of silt. Oxygen is used in the decaying process of organic matter, so vegetation entering and decomposing in the reservoir depletes the river downstream of oxygen, which can, in turn, suffocate healthy organisms and hinder their growth. As the waters build up behind the dam, and the environment is changed from a flowing river to a reservoir, the water temperature changes, altering both plant and fish life in downstream areas.