Too much of a Good Thing

In many parts of the world, periodic/seasonal flooding occurs due to a sudden peak in the volume of water carried by a river. For example, these conditions can be triggered when winter snow accumulations melt in the spring. Flooding can be a revitalizing force, like fire. Sediment deposited by a river helps enrich the soil. Because of this, people have tended to settle in the flood plains of rivers.

Deforestation contributed to flooding by reducing the ability of the habitat to absorb water. It may take several days for a heavy rain to make its way from a forested area into the neighbouring rivers. In an urban or agricultural area, it may take only a few hours. Wetlands, which provide buffer zones for excess water, have been "reclaimed" for other uses.

Dams were built to attempt to equalize water levels and so prevent flooding. However,

• often these dams cannot deal with unusually large peaks in water flow
• dams change the characteristics of the water - temperature, oxygen level and sediment load/nutrient levels
• dams require upkeep
• different groups may have conflicting requirements for water levels. For example, what is best for hydro-electric power may not be best for recreational boating.
• migration of fish is often blocked
• dams can introduce mercury into the food web
• habitat may be destroyed
• submerged trees and vegetation may release greenhouse gases such as methane or carbon dioxide
• stagnant water may provide a breeding ground for insects and disease

Flood Links

• Conservation Authorities - watershed management
• Floodplain Management
• Saguenay Flood - 1996
• another link about the Saguenay flood
• Red River Flood - 1997
• Flood! - PBS Nova
• U.S. Association of Dam Safety officials
• Cobb's Creek - a seasonal lake