Watershed Health
Floodplain Mapping
The NPCA is a watershed management agency. Our goals include protecting our communities from natural hazards, conserving our natural environment, and supporting our partners in creating sustainable communities. From a flood management viewpoint, the NPCA and our municipal partners rely on floodplain mapping for:
- flood forecasting and warning,
- emergency planning and response,
- prioritization and planning for flood mitigation works,
- community planning and land use decision making, and
- identifying the extent of the flood hazard.
What Is a Floodplain?
A floodplain is an area of land near water bodies (rivers, lakes, etc.) that is often flooded when the water body is too full. Examples of floodplains include low lying lands that are flooded or inundated with water when a river spills over its banks or when lake levels rise due to storm surge or significant precipitation. Floodplains are natural features that allow flow to spread across the landscape.
What Is Floodplain Mapping?
Floodplain mapping is used to identify areas that may be susceptible to river or coastal flooding during large storm events. Floodplain mapping relies on field surveys, engineering analysis and hydrologic and hydraulic modelling. Hydrologic modelling predicts how much stormwater will runoff the land during a rainfall event. Flows generated by the hydrologic model are then input into the hydraulic model which routes these flows through the river system to predict the peak flood depth.
What Standards Are Followed?
Analysis and floodplain mapping are undertaken in a manner consistent with the Ontario Ministry of Natural Resources and Forestry’s (MNRF) Technical Guide – River and Stream Systems: Flooding Hazard Limit (2002). This guideline sets out provincial expectations on analysis approaches applied in mapping the regulated flood hazard. The MNRF guideline is used by all Conservation Authorities undertaking flood hazard mapping.
Why Is Floodplain Mapping Important?
In Canada, floods account for the largest portion of disaster recovery costs on an annual basis. The first step to reduce the cost of flood damage within a community is to have mapping that accurately shows flood hazards. These maps help people prepare for and respond to potential flooding and make informed decisions about their own emergency plans, property improvements, and insurance needs.
Updating Floodplain Maps
The NPCA is working with our partners to reduce flood risk in our communities by updating floodplain maps, some of which are more than 30 years old. This will be a multi-year program and these updates will include comprehensive public consultation processes. When these floodplain mapping consultations are taking place, more information will be available at the link below.
Each year we undertake updates for several creeks in the Niagara Peninsula watershed. Learn more about these projects and how to provide feedback below.
What Is the Regulated Flood Hazard?
In the NPCA’s jurisdiction, the regulated flood hazard is defined in provincial legislation by the greatest flood extent associated with the 1 in 100-year storm event. This is the anticipated limit of flooding that has a 1% chance of occurring in any given year.
Does Flood Risk Extend Beyond the Regulated Flood Hazard?
While flood hazard mapping identifies the extent of the regulated floodplain associated with river or coastal flooding, it does not identify the full extent of flood risk. Flooding may be experienced outside of the defined river and coastal flood hazard for a variety of reasons, including occurrence of extreme rainfall events (which are greater than the regulatory 1 in 100-year storm event standard), formation of significant ice or debris jams and large beaver dams, or due to other flooding mechanisms such as urban flooding caused by rainfall that exceeds the capacity of local storm sewer systems.
Who is Responsible for Dealing with Urban Flooding?
Urban flooding is caused by rainfall that exceeds the capacity of local storm sewer systems. The local municipality is responsible for studying and addressing issues caused by their storm sewer system.
FREQUENTLY ASKED QUESTIONS
Does living in or near the floodplains affect my house insurance?
The Niagara Peninsula Conservation Authority’s goal is to produce accurate flood hazard maps using modern methods and up-to-date mapping of the study area all undertaken by experienced professional engineers. The NPCA uses these flood hazard maps to help direct new development away from areas that are flood prone. All of the NPCA’s flood hazard maps are posted on the NPCA’s website and the reports are freely available.
The NPCA has no control over how insurance companies implement their polices or set their rates. All insurance companies are different and some make wide assumptions regarding the location of a policy holder’s proximity to a flood hazard. The NPCA notes that flood insurance polices and premiums vary greatly between insurance companies. The NPCA would encourage landowners to speak to different insurance companies to find a policy that is right for their particular situation.
Will NPCA staff enter onto my property if I am in the floodplain?
Should the need arise during any floodplain mapping update project, the project team will obtain the landowner’s permission before entering onto private property.
Should permission not be obtained, the project team will not enter onto the property but will utilize alternative modelling methods to generate the floodplain.
Will updates to floodplain mapping near me impact my property value?
NPCA works with property owners to understand how they intend to use their property within the floodplain and if development approvals are required, to suggest solutions that balance the request with the need for risk management.
The NPCA cannot control impacts on property value and appreciates the perception that land within the floodplain has a lower value than land outside the line. As such, careful attention is given to the technical process of defining where the line falls and to ensuring that the flood line is technically accurate and defensible in order to ensure that public risk related to flooding has been minimized.
Is Climate Change considered in floodplain mapping update projects?
In the NPCA’s jurisdiction, the 100-year storm is the Regulatory storm event. The goal of this project is to understand the location of that 100-year flood line.
The NPCA through its new Strategic Plan 2021-2031, is committed to supporting evidence-based decision-making for climate-resilient watersheds and shorelines, and protecting people and properties from natural hazards and climate impacts.
NPCA’s floodplain models, reports and mapping are freely available and important information for NPCA and other public agencies, such as municipalities, to use when assessing the potential impacts of severe weather events as a result of climate change.