Flood Mitigation: Wetlands

Flood

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What is a wetland?

Photograph of a wetland with trees, grasses and water
Wetland. Photo by Luke Hodde on Unsplash

A wetland is an area of land that performs many ecosystem services one of them being the ability to retain water. Typically, there are five different kinds of wetlands including; bogs, fens, marshes, swamps, and shallow/ open water. Each wetland is characterized by the kinds of vegetation growing on or nearby the wetland, movement of water, and surrounding soil characteristics [1]. Wetlands are a critical part of our shared ecologies offering food and shelter for wildlife and contributing to the overall health of surrounding watersheds [2].

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

In the event of a flood, wetlands provide important services to mitigate the full impacts of high water. Wetlands are natural water retention areas that can store water while also slowing down the speed of flood waters. Additionally, forested areas if surrounded by wetlands help to hold flood waters further mitigating downstream flood damage. Providing a natural solution to flooding, wetlands also filter water, replenish groundwater sources and protect against erosion [3].

Do wetlands already exist in Alberta?

Wetlands are an important feature of Alberta’s landscape covering approximately 117,000 km2 of the Province. In particular, peatlands cover 103,200 km2 or 90% of the wetlands area [4].

What are the costs to build and maintain?

For naturally occurring wetlands, there is no cost to build and maintain. Due to major losses in wetland areas across Alberta, constructed wetlands have become an option. The costs associated with building wetlands vary depending on the size of the constructed wetland and vegetation needed. In a recent report, it was determined that the replacement cost of all wetlands in eastern Calgary and the surrounding region would cost approximately $338 million. An additional $2 million per year of lost value would also occur if existing natural wetlands continue to disappear at the current rate [5]. Furthermore, maintenance expenses can be 3% to 5% of the initial construction costs [6].

How long does it take to build?

Constructed wetlands do not take a long time to implement, however, constructed wetlands take many years to reach their full potential and function as ecological succession returns. While development projects continue to increase in Southern Alberta, there are risks of wetland loss which negatively impact water storage capabilities. For example, a recent report showed that in eastern Calgary, the Town of Chestermere and Rocky View County have experienced a 20% decrease in water storage capacity since 1965 [7]. While wetlands could be built relatively quickly, the full function and benefit of constructed wetlands would not be felt for years to come.

Lifetime expectancy of wetlands?

Wetlands have been part of our landscape for millions of years, however, significant developments in Alberta have caused harm and destruction to these historic wetlands [8]. As a natural part of the landscape, wetlands have a long-term and integral role in maintaining ecosystem health.

What are the associated risks?

Generally, wetland’s ability to function is not altered by significant water volumes or lack thereof from drought due to their ability to retain and store significant amount of water. With that said, if wetlands are inundated with too much water or dehydrated as a result of too little water, over time this can compromise their ability to function potentially causing permanent damage to their ecosystem [9]. Disrupting the natural cycle of wetlands risks their ability to retain, store and filter water.

What are the impacts on the surrounding watershed system and environment?

In the event of a flood, wetlands provide numerous benefits to the surrounding watershed and overall environment. Wetlands provide an important filtration system that can reduce impurities in the water and recharge groundwater supplies to make more room for flood waters. Wetlands also prevent soil and riverbank erosion while retaining flood waters and slowly releasing them downstream [10].

Would a wetland help in a drought?

Yes, wetlands are extremely valuable in the event of a drought because water is retained and slowly released. Up-land wetlands can supply a network of seeps and springs which help to maintain healthier river base flows during drought. Wetlands also provide an important source of water to livestock and the surrounding environment in times of drought [11].

Sources

  1. “What is a Wetland?” Ducks Unlimited Canada. Accessed November 18, 2013. http://www.ducks.ca/learn-about-wetlands/what-wetland/
  2. “What is a Wetland?” Wetlands Alberta. Accessed November 18, 2013. http://www.wetlandsalberta.ca/what-is-a-wetland/
  3. “What do Wetlands do?” Ducks Unlimited Canada. Accessed November 18, 2013. http://www.ducks.ca/learn-about-wetlands/what-do-wetlands-do/  
  4. “Alberta’s Wetland Policy.” Aquality. Accessed November 18, 2013. http://www.wetlandpolicy.ca/ 
  5. “Ecosystem Services Approach Pilot on Wetlands.” Integrated Assessment Report. Government of Alberta. October 2011 (pg. 7).
  6. “Stormwater Management Fact Sheet: Stormwater Wetland.” Stormwater Centre. Accessed January 21, 2014. http://www.stormwatercenter.net
  7. “Ecosystem Services Approach Pilot on Wetlands.” Integrated Assessment Report. Government of Alberta. October 2011 (pg. 7).
  8. “Alberta’s Wetland Policy.” Government of Alberta. Accessed January 21, 2014. http://www.wetlandpolicy.ca/
  9. “Wetland Loss.” Wetlands Alberta. Accessed January 21, 2014. http://wetlandsalberta.ca/wetland-loss/ 
  10. “Wetland Values.” Wetlands Alberta. Accessed January 21, 2014. http://wetlandsalberta.ca/wetland-values/
  11. Ibid.

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