Wetlands as a Tool for Flood Control and Prevention 

If you live in British Columbia or have loved ones living in B.C., you will have heard about the devastating floods occurring across southern parts of the province. The Province of B.C. declared a state of emergency on November 17, 2021, following massive flooding and landslides caused by record-breaking rainfall throughout mid-November. 

Many communities in B.C. have been devastated by massive floods, including Abbotsford, Chilliwack, Merritt, Princeton, Lillooet, the Cowichan Valley Regional District and more.

Regional Districts affected by flooding in B.C., November 2021. (Emergency Management B.C.)

Nearly 18,000 people were ordered to evacuate from dozens of communities with several more under evacuation alerts. For instance, those living in the Sumas Prairie were put under evacuation order due to potentially catastrophic flooding, and the entire 7000 population of Merritt was ordered to evacuate on November 15, 2021. Highway 8 between Merritt and Spences Bridge in the Southern Interior suffered catastrophic damage and all those living in the area were evacuated. Many other communities such as Hosmer (RDEK A), Pemberton, Hope, Tulameen, and Keremeos spent days on evacuation alert with residents ready to leave on a moment’s notice if conditions worsened.

Many of the communities that were heavily impacted by the floods are built in floodplains or where wetlands have been drained. Across North America, wetlands, or “wastelands” as they were formerly referred, were considered a dangerous nuisance by many settlers throughout the 1700s into present day, since they often flooded which ruined crops and made harvesting difficult, and poorly functioning wetlands were a breeding ground for mosquitoes. These beliefs led to extensive draining of wetlands across the continent, and some developed regions of British Columbia, such as the Lower Mainland, Fraser Valley and Okanagan, saw a loss of up to 80% of wetlands ecosystems.

Example of wetland loss in valley bottom/urban areaMap of wetland loss in the Fraser Valley, B.C. since the early 1800s. Blue is where wetlands used to exist on the land, while red and purple are what remain.
Maps showing changes (92% loss) in the water birch – red-osier dogwood riparian shrub swamp wetland (BD) ecosystem between 1800 and 2005 in the Okanagan. (Source: Lea 2008)

When wetlands or floodplains are drained, it is done so through ditches, diking, drainage tiles, and/or pumps. When big precipitation or flooding events occur, like what happened in November 2021, these lands can quickly become saturated again, overflowing and overwhelming the drainage mechanisms that were put in place.

Drainage of wetlands can have significant environmental impacts, such as destabilization and erosion of soils, loss of available water to wildlife and communities, loss of carbon sequestration, and loss of flood protection. Wetlands act like giant, natural sponges and store large amounts of rainwater and gradually release it to surrounding streams and into the groundwater table. For a better understanding, a one-acre wetland can typically store about three-acre feet of water, or one million gallons (3785411 litres of water). An acre-foot is one acre of land, about three-quarters the size of a football field, covered one foot deep in water. To learn more about the ecosystem services that wetlands provide and how they can help mitigate flood impacts, watch this short video by BC Tomorrow.

Canada’s wetlands provide flood control worth $2.7 billion annually.

National Wetlands Working Group, 1988
Wetland functions for flood mitigation and water retention (Queensland Department of Environment and Science)

Drained wetlands are often some of the most productive agricultural lands thanks to the nutrient cycling processes that naturally occur in wetlands. For example, the Sumas Prairie, located in the Fraser Lowlands, is one of the most productive farming regions in the country thanks to its rich and fertile post-wetland soils. As shown in the maps below, the City of Merritt and Town of Pemberton are located in the floodplains of the Nicola and Lillooet Rivers, respectively. 

Unfortunately, these drained wetlands impact more than just wildlife and fish; for example, Semá:th Xo:tsa (Sumas Lake) was referred to as the heart of the Semá:th peoples (Sumas First Nation) because it was like a grocery store with its abundance of fish, plants, and animals, including species such as sturgeon, trout, and the now rare white-fronted goose. The Sumas Lake and surrounding wetlands have been drained for over 100 years and continue to be drained thanks to the Vedder and Sumas Canals, Barrowtown Pump Station, and over 40km of flood protection dikes. These systems are keeping the wetlands and lake from reforming by diverting precipitation and excess groundwater into creeks, while also keeping the Fraser River from entering the Sumas Prairie.

Sumas Lake before and after draining in the 1920s (The Reach Gallery)

Of course, agricultural land is necessary to help feed our communities, and having local agriculture is important for food security. Farmers also need water, which wetlands help secure. The way forward is to learn how to preserve wetlands on the landscape while also supporting local agriculture.

The BCWF has partnered with many private landowners and farmers to restore wetlands on their properties, often in areas of their land that were unproductive due to constant saturation. A great example of this type of partnership is Curly Frog Farm in Kelowna, B.C. This farm is an agricultural initiative that supports both farmland and wetland in the beautiful Okanagan Valley flatlands. The landowner, Brenda, noticed just one year after wetland restoration that the wetlands were helping with flood control on her property.

Well managed and intact wetlands offer a variety of benefits to farmers, including:

  • Recharging deep aquifers which provide groundwater for livestock use and crop irrigation;
  • Reducing erosion and maintaining soil productivity;
  • Maintaining water quality thus increasing animal health when using local water sources;
  • Increasing soil moisture and therefore helping increase crop yields; and
  • Provide nutrients for crops from the breakdown of organic matter.

Agricultural production benefits when the environmental functions and economic values of wetlands are incorporated into planning. Rather than continuing to drain wetlands to create agricultural land, it’s time to find a balance where the two can coexist.

These flooding events show us how important intact wetlands and floodplains are, and BCWF hopes to support education and legislation that highlight the importance of wetlands as tools for flood control and prevention, among other benefits to communities.

Our sincerest condolences to all those in British Columbia who have been affected by the recent flooding. For those that would like to donate to help those impacted by this most recent disaster, please consider organizations like the B.C. Food Bank, or other local relief efforts.

For more information on the protection and management of wetlands that are on or near agricultural lands, see: Wetland Ways: Interim Guidelines for Wetland Protection and Conservation in British Columbia

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