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Terminology

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1 in 100 Year Flood Event
A 1 in 100 year flood event is a flood event that has a 1% probability of occurring in any given year.

Flood fringe The portion of the flood hazard area outside of the floodway. Water in the flood fringe is generally shallower and flows more slowly than in the floodway.

Flood mitigation For the purpose of this project, flood mitigation involves the management and control of flood water movement, such as redirecting flood run-off through the use of dykes and flood gates.

Floodway The portion of the flood hazard area where flows are deepest, fastest and most destructive. The floodway typically includes the main channel of a stream and a portion of the adjacent overbank area. The floodway is required to convey the design flood.

Freeboard A factor of safety usually expressed in metres above a flood level for purposes of floodplain management. Freeboard tends to compensate for the many unknown factors that could contribute to flood heights greater than the height calculated for a selected size flood and floodway conditions, such as wave action, bridge openings, and the hydrological effect of urbanization of the watershed.

Overland flow Areas of overland flow are part of the flood hazard area outside of the floodway, and typically considered special areas of the flood fringe.

Storm gate A storm gate or valve is a gate or valve that is installed inside or onto the outlet of a storm outfall. While they are available in numerous varieties, a storm gate or valve can either be closed manually or designed to only open when the flow is coming from within the storm sewer system. They become an important part of a flood mitigation strategy as they prevent the backflow of flood waters into the storm sewer system and up onto city streets.

Storm outfall A storm outfall is the discharge point for a storm sewer system into a body of water such as a river, creek, or pond.

Storm sewer A storm sewer is a network of pipes, manholes, catch basins, etc. that is designed to drain excess storm water off of roadways, properties and other developed area.