PUBLISHED: 29 November 2013

Flood Mitigation: Dams

What is a dam?

A dam is a constructed barrier built across rivers and streams to detain water eventually creating a lake or a reservoir. Dams are built to produce electricity as well as divert and control the flow volumes. There are three commonly used dam designs: embankment, gravity, and arch designs, which are used depending on local topography and the hydrological system[1]. Made from concrete, dams hold back water resulting in storage that allows for electricity generation, water supply for agriculture, municipalities, and drought. Dams are also designed to control flow volumes enabling them to act as a tool for flood mitigation.

How does this option help to mitigate the impacts of a flood?

While dams can be used to generate electricity and store water for future uses such as irrigation, this infrastructure can potentially be used in response to flooding. Dams are capable of holding water back when needed and releasing water into spillways when levels have become too high. Prior to rainy or wet seasons, the operators of a dam will lower the level of water in the reservoir to make room for anticipated precipitation. As a result, the full effects of a flood are mitigated further protecting downstream areas[2].

Are dams already built in Alberta?

There are numerous dams located throughout Alberta of differing size. On the Red Deer River, the Dickson Dam is owned by Alberta Environment and is primarily used for water storage and flow control. The Bow River Basin (and its’ subsequent tributaries) contain eleven dam structures owned and operated by TransAlta Corporation. The main function of these dams is electricity generation[3], although they do play a role in flood control. The Oldman River dam is owned and operated by Alberta Environment and is used for water management and flood control.

What are the costs to build and maintain?

Depending on the size of dam structure construction costs will vary, however, this form of flood mitigation is typically one of the more costly. Large dam projects can cost anywhere between $1 and $6.5 billion[4] while smaller dams will cost less.

How long does it take to build?

Construction times vary depending on the dam project. For example, the large Hoover Dam in Nevada took five years to construct while the Glenmore Reservoir and Dam in Calgary took one year to construct[5][6].

Operations lifetime expectancy?

Dams are exposed to routine and ongoing maintenance to prevent failure. The average lifetime of a dam is 50 years before required upgrading and major maintenance or overhauls should occur[7].

What are the associated risks?

Most common is the risk of dam failure caused by structural, mechanical or hydraulic failures. This includes; inadequate design, malfunctioning dam components, spillway damage, seepage issues, embankment and stability problems, and improper operation[8]. The result of these failures in the past has been significant with loss of life, infrastructure damage and extensive flooding. Pursuant of these risks is the deficient status of dams currently in operation throughout Canada and the U.S. where significant upgrades are needed to prevent failures[9].

What are the environmental and watershed impacts of a dam?

The environmental impact of a dam is significant due to the disruption of the ecosystem’s interconnectedness, especially in terms of aquatic species migration, habitat and the surrounding environment[10]. Wetland destruction can also occur further impacting forests, wetlands and wildlife due to permanent inundation of the surrounding ecology. Dam construction can lead to the extirpation of plants and aquatic species due to insufficient water flows in rivers or streams, change in water temperatures, water quality and sediment movement[11]. The direct impact of a dam on the overall watershed is immense due to the structural disruption of the basin’s functioning ecosystem.

Would a dam help in a drought?

Dams are typically built for hydroelectricity production, flood mitigation or water storage. From the perspective of water storage, dams provide infrastructure to manage drought conditions by providing storage and the slow release of water[12]. Therefore, maintaining and forecasting the release of water stored in dam reservoirs contributes to drought defences. In Alberta, however, multi-purpose dams have not been built to mitigate both flooding and drought conditions at once. Such infrastructure would require specific operating rules to provide benefits for both flood and drought mitigation.

[1] “Dams: What they are and what they do.” International Rivers. Accessed November 18, 2013. 

[2] Ibid.

[3] “The Purposes of the Existing Dams in the SSRB: Information Sheet.” Alberta Environment and Sustainable Resource Development. Published October 17, 2007. Accessed November 18, 2013.  

[4]  Brown, Paul. “The unacceptable cost of big dams.” The Guardian. Published November 17, 2000. Accessed February 4, 2014.

[5] “Hoover Dam: Frequently Asked Questions and Answers.” U.S. Department of the Interior. Bureau of Reclamation. Last reviewed December 2008. Accessed January 15, 2014.  

[6] “Glenmore Reservoir.” Atlas of Alberta Lakes. Accessed January 14, 2014.

[7] “Dams: Dam Demolition Background.” MIT. Mission 2012: Clean Water. Accessed January 15, 2015. 

[8]  “Living with Dams: Know your risks.” FEMA. Published February 2013. (Pg. 9). 

[9]  Ibid. 

[10]  Ibid. 

[11]  “How are Watersheds Impaired?” EPA. Accessed January 16, 2014. 

[12]  “Storing and moving water.” National Drought Mitigation Centre. Accessed January 16, 2014.