The term floodplain refers to the low area adjacent to a river that is subject to periodic flooding. Floodplain protection tools can be used to protect aquatic and riparian (shoreline) habitats, reduce the risk of property damage during flood events and protect public safety.
Recommended Practices
Stormwater management. Managing stormwater onsite in uplands will help reduce flood contributions from urban runoff. Stormwater can be managed through bioinfiltration techniques and stormwater wetlands.
Flood forecasting and flood preparedness. Early warnings of floods will help reduce damage to properties and infrastructure. Create a flood response plan to effectively respond to flood conditions.
Use infrastructure to manage/mimic floods. Dams present on the river allow for controlled flooding that can mimic the pre-development hydrology/hydrograph.
Protect floodplains. Determine which uses are acceptable in the floodplain (e.g., recreation, open space, natural areas) and establish land use bylaws and policies to prohibit new development in either floodway or flood fringe and restrict damage compensation to landowners that contravene these bylaws.
Restore degraded floodplains to ensure they are performing optimally. Restoration includes restoring pre-disturbance physical, biological and chemical functions of the floodplain. Employing the expertise of a wetland biologist or engineer is recommended to ensure the ecological integrity of the restored floodplain is maximized and its ecosystem services (including flood attenuation) are reestablished.
- Consider landscape ecology to ensure the floodplain restoration takes into account regional and watershed-level hydrological, ecological and climate conditions.
- Establish a self-sustained ecosystem with a focus on ecological function and minimal engineered elements. This will save maintenance costs in the long-term and ensure the intended ecosystem service provision will be maximized in the floodplain.
- Factor in time for floodplain and wetland plants to undergo natural processes of succession and variable water levels over time. Restoration can be a long process and sufficient time needs to be planned for.
- Involve the local community to ensure the public is aware of the importance of the restoration and invested in its success.
Flooding by design. Combine flood detention areas with parks and green spaces.
Financial incentives have been successfully used in some jurisdictions. For example, imposing a “flood tax” on residents who live in the floodplain can provide municipalities with a reserve of funds to offset compensation payments and to develop progressive flood management tools. Insurance companies can also provide deterrents to development in floodplains. This can work in the following ways:[1]
- Identifying areas of risk
- Catastrophe modelling
- Economic disincentives to construction in floodplains
- Benefit cost appraisals that incorporate collected data on costs of flood damage
- Promoting resilient reinstatement techniques
- Promoting temporary defense solutions
Education and awareness. Recognize ecological benefits from flooding and raise awareness about the role and function of floodplains.
Project Considerations
Existing development. It is often necessary for municipalities to “grandfather” previous developments in floodplains. Municipalities can explore land-use planning tools such as density bonusing, land swaps and cluster development to restrict development in the most sensitive flood-prone areas to protect the floodplain and property and infrastructure from risk.
Many municipalities should consider updating floodplain maps, especially in light of projected increases in flooding due to climate change. Municipalities may also want to adjust the risk tolerance they are willing to accept for delineating flood zones in communities. For example, most floodplain maps detail the 1 in 100-year flood, but inevitably, and more frequently than before, this is being exceeded. Maps that delineate the 1 in 500-year or 1 in 1000-year flood may be more useful for preventing flood damage.
The Business Side
Restricting or prohibiting new development in floodplains (flood way or flood fringe) can save long-term costs related to maintenance of flood prevention structures, damage to infrastructure and flood compensation payments. Maintaining healthy floodplains and riparian buffer areas can also increase property values adjacent to green spaces, which can in turn provide more property tax revenue to municipalities.
The Nature Side
Flooding is a natural process that benefits riparian areas and the wildlife that depend on them. Many of Alberta’s species at risk depend to some degree on riparian habitats along rivers, lakes and wetlands. Protected or restored floodplains can increase biodiversity and their vegetation contributes to greenhouse gas sequestration. Allowing river water that is high in suspended sediments to flow over the floodplain helps to slow the water and allows these sediments to settle out, thereby improving water quality and enriching floodplain soils. By allowing flooding through this example of NBS, municipalities can help protect shorelines and prevent scouring and erosion that can occur when high volumes of flood water are forced to move through a restricted flood channel over a short amount of time.
The Community Side
Protecting and restoring floodplains shields property and infrastructure from damage due to flooding. Preventing development in these areas can potentially lead to lower insurance rates for adjacent property owners. Healthy riparian areas and floodplains also add green space to communities, which can have a host of benefits, including potential for recreation, wildlife and bird viewing, improvements to physical, mental and social health for residents, and increased property values.
[1] Crichton, D. 2008. Role of Insurance in Reducing Flood Risk. The Geneva Papers on Risk and Insurance-Issues and Practice 33, 117–132.
Crichton, D. 2008. Role of Insurance in Reducing Flood Risk. The Geneva Papers on Risk and Insurance- Issues and Practice 33, 117–132.
Primeau, S., Bell, M., Riopel, M., Ewaschuk, E., & Doell, D. 2009. Green Communities Guide: Tools to Help Restore Ecological Processes in Alberta’s Built Environments. Land Stewardship Centre of Canada.
University of Michigan. n.d. Floodplain Restoration Principles. School for Environment and Sustainability, University of Michigan.