Water Stewardship


Floodplain Mapping Definitions

For more detailed definitions, see "Canada/British Columbia Agreement Respecting Floodplain Mapping" (amended Aug. 2, 1994)

Designation: a declaration of a floodplain by the federal and provincial Environment Ministers, within which floodproofing measures are required.

Designated Flood: a significant historic flood or a flood having a 200-year recurrence interval based on analysis of historic flow records.

Flood fringe: the portion of the floodplain not in the floodway to which floodproofing requirements apply.

Flood level: the calculated elevation of the designated flood, including an allowance for uncertainty (freeboard) based on site specific conditions.

Floodplain: a lowland area, whether dyked, floodproofed, or unprotected, which is at an elevation susceptible to flooding.

Floodproofing: the alteration of land or other precautions to reduce flood damages. Floodproofing may include adding fill to raise the elevation of a building site, structural measures such a foundation walls or columns to raise a building, or combinations of fill and structural measures. Floodproofing includes the use of setbacks to maintain a floodway and allow for erosion.

Floodway: the channel of the watercourse and those portions of the floodplain which are reasonably required to convey the designated flood.

Freeboard: a vertical distance added to the actual calculated flood level to accommodate uncertainties (hydraulic and hydrologic variables), potential for waves, surges, and other natural phenomena.

Interim Designation: a declaration of a floodplain by the federal and provincial Environment Ministers, within which floodproofing measures are required. An interim designation is made if the Ministers are satisfied the mapping is adequate but may not fully comply with the procedures set out in the agreement.

Natural Boundary: means the visible high water mark of any lake, river, stream or other body of water where the presence and action of the water are so common and usual and so long continued in all ordinary years as to mark upon the soil of the bed of the lake, river, stream or other body of water a character distinct from that of the banks thereof, in respect to vegetation, as well as in respect to the nature of the soil itself. In addition, the natural boundary includes the best estimate of the edge of dormant or old side channels and marsh areas.

Setback: a distance which an undertaking or landfill must be set back from a natural boundary or other reference line to maintain a floodway and allow for erosion. The minimum required setback is 30 metres from the natural boundary unless otherwise approved.

Undertaking: the use of land, including the construction of, or major addition to, any structure.