Definitions

Watercourse: an identifiable depression in the ground in which a flow of water regularly or continuously occurs. (CAA, 1990)

Floodplain: the area, usually low lands adjoining a watercourse, which has been or may be subject to flood hazards. (MMAH, 2005)

Riverine Flood Hazards: In Ontario, storm-centred events, flood frequency based events or an observed event are used to determine the extent of the flood hazard limit. Credit Valley Conservation manages lands containing flood hazards within CVC’s jurisdiction based on the greater of the regional storm event as identified by the Province (Hurricane Hazel) or the one hundred year flood. The flood determined through this calculation is the Regulatory Flood and defines the extent of the riverine flood hazard.

Credit Valley Conservation applies and recommends various policy approaches for managing flood hazards within the CVC’s jurisdiction as follows:

One Zone Concept: unless determined to be appropriate by the affected municipality and identified through a comprehensive environmental study approved by the relevant agencies, CVC will apply a one zone concept to floodplain management based on the regulatory flood standard, in accordance with Provincial standards. In a one zone concept the entire area within the flood hazard limit is considered to be one management unit, and is referred to as the floodway (see Figure 6). The one zone concept is the most restrictive and effective way to manage flood hazards from a risk management perspective.

Flood Hazard Limit for One Zone Policy Approach.

Two Zone Concept: where the affected municipality has determined it appropriate to apply a two zone concept and a comprehensive environmental study has been approved by the relevant agencies, CVC will apply a two zone concept to floodplain management in accordance with Provincial standards and the approved municipal two zone concept policies. The two zone concept separates the floodplain into two main components (see Figure 7):

  1. the floodway – the portion of the floodplain where development (1, 2) and site alteration would cause a danger to public health and safety or property damage. Generally, development (1, 2) and site alteration will not be permitted within the floodway; and
  2. the flood fringe – the portion of the floodplain that could potentially be safely developed or altered with no adverse impacts. Development (1, 2) and site alteration may be permitted within the flood fringe, subject to satisfying specific conditions.

In addition to the above, the two zone concept is not intended to be considered on a lot-by-lot basis, but on a subwatershed or major reach basis considering several community related and technical criteria as outlined by the Province including local need, changes in land use, administrative capability, constraints to the provision of services, frequency of flooding, physical characteristics of the valley, impacts of proposed development (1, 2) (flood levels at the site, upstream, and downstream), feasibility of floodproofing, and ingress and egress.

Flood Hazard Limits for Two Zone Policy Approach.

Currently, there are 2 areas within CVC’s jurisdiction where the two zone concept has been approved for application. This includes specific portions of flood prone areas associated with Mill Creek and Lower Menora Creek in the Town of Orangeville, and specific portions of flood prone areas associated with Cooksville Creek in the City of Mississauga. The site specific policies and mapping for the approved two zone areas in Orangeville and Mississauga are outlined in Appendices B and C respectively.

Special Policy Areas: where the affected municipality has determined it appropriate to apply a special policy area and the Ministers of Municipal Affairs and Housing and Natural Resources have approved the designation, CVC will apply the special policy area concept, in accordance with Provincial standards and the approved municipal special policy area policies. Generally, special policy areas may be considered where flood remediation strategies and two zone concept approaches have been deemed not practical, and adhering to the one zone concept will impose significant social and economic hardship to the historically existing floodprone community. It is important to note that special policy areas are not intended to facilitate new or intensified development (1, 2) and site alteration if the community has feasible opportunities for development (1, 2) outside of the floodplain.

Where a special policy area is applied, the relevant agencies agree to reduce Provincial floodproofing standards and accept a higher level of risk. Similar to the two zone floodplain policy approach, a special policy area is not intended to be considered on a lot-by-lot basis, but on a subwatershed or major reach basis considering several community related and technical criteria such as municipal commitment, designated growth centre, infrastructure investment, limited alternatives, flow characteristics, frequency of flooding, floodproofing measures, upstream and downstream effects, frequency of ice jams, berms and flood walls, and reduced flood standards. Currently, there are no approved special policy areas within CVC’s jurisdiction.

Floodplain Spill Areas: There are several areas within the CVC’s jurisdiction where floodplain spills occur. Spill areas are portions of the floodplain where hydraulic modeling and mapping of the riverine flood hazard indicates that flood waters are not physically contained within the valleyland and may or may not exit the watershed or subwatershed into surrounding lands. It is important to note that floodplain spill areas do not include the flood fringe, regardless of its characteristics such as flood flows and depths. Generally, the depth of flooding in spill areas cannot be readily determined as the flood depths that occur depend on a number of factors such as local and down-gradient topography, storage volume and the amount of spill flow that occurs. In addition, spills typically occur during higher flow rates of the storm event where the volume and depth of flood water is also dependant on the duration of the storm event.

Valleyland: land that has depressional features associated with a river or stream, whether or not it contains a watercourse. (CAA, 1990)

Riverine Erosion Hazards: Credit Valley Conservation determines the extent of riverine erosion hazards based on whether or not a valleyland is defined or undefined, and whether or not the valley slopes are stable, unstable and subject to toe erosion.

Defined Valleylands Where the Valley Slopes are Stable: the limits of the erosion hazard consist of the valleyland extending to the top of stable slope.

Extent of riverine erosion hazard where the valley slopes are stable.

Defined Valleylands Where the Valley Slopes are Unstable With a Stable Toe: the limits of the erosion hazard consist of the valleyland extending to the top of stable slope projected from the existing stable toe of slope.

Extent of riverine erosion hazard where the valley slopes are unstable with a stable toe.

Defined Valleylands Where the Valley Slopes are Unstable With Active Toe Erosion: the limits of the erosion hazard consist of the valleyland extending to the top of stable slope projected from the stable toe of slope.

Extent of riverine erosion hazard where the valley slopes are unstable with active toe erosion.

Undefined Valleylands: the limits of the erosion hazard consist of the maximum extent of the meander belt allowance of the watercourse.

Extent of riverine erosion hazard for undefined valleylands.

Lake Ontario Shoreline Hazards: The Lake Ontario flood hazard, erosion hazard, and dynamic beach hazard limits are determined based on information from the most recently approved shoreline hazard plan on a reach basis, based on the following parameters:

Lake Ontario Flood Hazards: flooding from Lake Ontario affects the entire shoreline area. The Lake Ontario flood hazard limits consists of:

  1. the one hundred year flood level;
  2. the appropriate allowance for wave uprush; and
  3. the appropriate allowance for other water related hazards.

Lake Ontario shoreline flood hazard limits.

Lake Ontario Erosion Hazards: the Lake Ontario erosion hazard limits are determined by using the one hundred year erosion rate in accordance with Provincial standards, and consists of the combined effects of:

  1. toe erosion allowance; and
  2. stable slope allowance projected from the stable toe of slope.

Lake Ontario shoreline erosion hazard limits.

Lake Ontario Dynamic Beach Hazards: the Lake Ontario dynamic beach hazards are portions of the shoreline where accumulated unconsolidated sediment continuously moves as a result of naturally occurring processes associated with wind, water and changes in the rate of sediment supply. The Lake Ontario dynamic beach hazard limits consists of the combined effects of:

  1. one hundred year flood level;
  2. an allowance for wave uprush; and
  3. an allowance for dynamic beach processes.

Lake Ontario dynamic beach hazard limits.

Wetlands: land that:

  1. Is seasonally or permanently covered by shallow water, or has a water table close to or at its surface,
  2. Directly contributes to the hydrologic function of a watershed through connection with a surface watercourse,
  3. Has hydric soils, the formation or which has been caused by the presence of abundant water, and
  4. Has vegetation dominated by hydrophytic plants or water tolerant plants, the dominance of which has been favoured by the presence of abundant water

but does not include periodically soaked or wet land that is used for agricultural purposes and no longer exhibits a wetland characteristic referred to in clause (3) or (4). (CAA, 1990)

Hazardous Lands: land that could be unsafe for development (1) because of naturally occurring processes associated with flooding, erosion, dynamic beaches or unstable soil or bedrock. (CAA, 1990)

Development (1): as it pertains to the Conservation Authorities Act, means:

  1. the construction, reconstruction, erection or placing of a building or structure of any kind;
  2. any change to a building or structure that would have the effect of altering the use or potential use of the building or structure, increasing the size of the building or structure or increasing the number of dwelling units in the building or structure;
  3. site grading; or the temporary or permanent placing, dumping or removal of any material, originating on the site or elsewhere. (CAA, 1990)

Development (2): as it pertains to the Planning Act, means the creation of a new lot; a change in land use; or the construction of buildings and structures, requiring approval under the Planning Act, but does not include: (a) activities that create or maintain infrastructure authorized under an environmental assessment process; (b) works subject to the Drainage Act. (MMAH, 2005)

For additional definitions please refer to Chapter 8 of CVC’s Watershed Planning and Regulation Policies or Ontario Regulation 160/06.