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Floodplain Mapping

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Conservation Authorities are responsible for floodplain management. Identifying lands that are vulnerable to flooding is an important responsibility for Ontario’s Conservation Authorities. Accurate engineered flood plain mapping is the foundation of effective flood plain management. In eastern Ontario, the 1:100 year flood plain is the regulatory standard calculated as having a 1% chance of occurring in any given year. Conservation Authorities use the mapping in the administration of regulations made under the Conservation Authorities Act.

What is a Floodplain?

Floodplains are low lying areas near watercourses that are naturally subject to flooding.

Why Map Floodplains?

Mississippi Valley Conservation Authority protects people and property from natural hazards. A natural hazard includes risks such as flooding and unstable slopes. The regulatory flood standard for the Mississippi Valley watershed is a 1:100 year flood event.

What is a 1:100 year flood?

A 1:100 year flood is a major flood that risks causing serious damage to people and property. These major floods have a 1% chance of occurring in any given year. To compare, a 50 year flood has a 2% chance of occurring in any given year. Simply because a major flood occurs does not mean that it cannot reoccur the next year.

How are Floodplains Mapped?

Floodplain maps are produced using a science-based method of field surveys and computer models. Background data is gathered on: land use; topography; stream flow; and precipitation. Field surveys collect information on local infrastructure (culverts, bridges, etc.). Data is then entered into computer models to calculate stream flow and water levels. Review of technical work and modelling is completed to finalize the floodplain map.

How are Floodplain Maps Used?

Floodplain maps establish protection areas to guide development projects to safe areas. Property owners may reduce the risk of flooding through options such as: raising building envelops; directing development outside of the floodplain, and using appropriate design. Mississippi Valley Conservation Authority works with property owners on solutions for their projects.