Floodplains in Alberta: A Tapestry of Geology and Ecology

AWC-WPAC, Science, and Watershed Issues | flood mitigation and floodplain | June 2024

What is a Floodplain?

A floodplain is the low, flat region of land that flanks a river from its banks to the outer edges of a valley. The floodplain consists of two regions: the floodway – the river or stream channel – and the flood fringe – the area that covers the banks to the bluff where water flows onto the land when a flood event occurs.

How are they formed?

• Floodplains are formed when a river meanders and by a combination of erosion – sediment is removed by the movement of water across the plain – and aggradation – sediment is deposited by the movement of water across the plain.
• Sediment compositions vary based on the land surrounding the floodway and the velocity of the channel.
• Higher velocities deposit coarser sediments such as gravels and lower velocities deposit finer sediments like clays, silts, and sands.
• These layers of variable sediments create aquifers that allow a filtration system for surface runoff to move downward to groundwater.  

What do Floodplains do for us?

For centuries humans have built societies from settlements established in floodplains. These regions have naturally nutrient rich, fertile soils that allow increased agricultural yields/food production and provide easy access to water for recreational/cultural activities.

Some benefits of healthy, natural floodplains are:

1. Flood protection
   • Reduction in economic loss relating to flood recovery and prevention – implementation and maintenance of flood deterrent infrastructure (e.g. floodwalls or levees)
   • Healthy riparian areas can lower the level of erosion/sediment suspended in the river, as well as aid with flood conveyance – reduction in the number and severity of flood events
2. Water Quality
   • Taking advantage of natural bank filtration – using natural riparian areas and floodplain sediment layers to filter out excess nutrients and sediments that can degrade water quality from channel/groundwater – is more cost effective than the time and materials needed to create filtration infrastructure
   • Natural, cost-efficient way of processing stormwater
   • Natural solution to water quality issues caused by anthropogenic activity
3. Agriculture
   • Flood resistant crops help with reducing severity of floods and increase water storage to combat drought
   • Floods allow an increased range for water to reach both over and under land
   • Floodplains provide natural buffers to rivers/streams for livestock
4. Drinking water
   • Many communities rely on groundwater for a source of drinking water and crop irrigation, healthy floodplains create a natural filtration system that recharges aquifers and replenish underground sources of water.
5. Increased habitat for wildlife
   • Floods can generate islands, oxbows, and new channels that increase habitat for fish, water birds, and other wildlife
   • Floods can also have a positive effect on native species by clearing out invasive species less suited to the natural environment
   • Flooding can be an essential step in fish and plant reproductive cycles (e.g. periodic flood events are used by certain willow species (Salix sp.) to distribute and germinate seeds) (Karrenberg et al., 2002).

Learn More About Floods and Floodplains

Alberta Environment and Parks – Alberta River Basins flood alerting, advisories, reporting and water management

Final flood studies and maps | Alberta.ca

Flood Awareness Map Application (alberta.ca)

Flood preparedness | Alberta.ca

Pembina Watershed Restoration Program | Athabasca Watershed Council (awc-wpac.ca)

Fun Fact!

Alberta is home to more than 260 fossil bonebeds (Eberth 2015). A bonebed is an assemblage of fossils and can be formed by flash flood events that collected and buried a great number of animals. These assemblages can not only tell us about the changes to biodiversity over time, but the geologic history of these floodplains can be read in the preserved layers of sediment. Coarseness and composition of sediments can show water characteristics seasonally as well as flood events. Observing frequency or even predictability of these events can help scientists make comparisons to modern systems and make predictions for future floods.

References:

Eberth DA (2015) Origins of dinosaur bonebeds in the Cretaceous of Alberta, Canada. Canadian Journal of Earth Sciences. 52(8): 655-681. 

Karrenberg S, Edwards PJ, Kollmann J (2002) The life history of salicaceae living in the active zone of floodplains. Freshw. Biol. 47 733–748. 

Maliva RG (2020) Riverbank Filtration. In: Anthropogenic Aquifer Recharge. Springer Hydrogeology. Springer, Cham. (5) 647-682

Benefits Of Healthy Floodplains (nature.org)

Why We Need to Restore Floodplains (americanrivers.org)

Flood Awareness Map Application (alberta.ca)

Final flood studies and maps | Alberta.ca

Flood preparedness | Alberta.ca

Pembina Watershed Restoration Program | Athabasca Watershed Council (awc-wpac.ca)