Impact of Flooding or Ignoring Flood Hazards
What are some of the impacts of flooding or ignoring flood hazards?
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Obstructing the flow, or reducing the flood storage can create
new hazards and aggravate existing hazards
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People may be cut off from emergency services, such as fire and police
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People's lives can be in serious danger
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Structures and buildings may fail
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Hazardous substances can be released to the environment
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The emotional toll on people can be heavy
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The economy of a region can sufferPublic money has to be spent on protection works and warning systems,
To learn more about flooding, floodproofing and flooding related terminology please consult the following information on flooding, which has been prepared by Environment Canada:
www.ec.gc.ca/water/en/manage/floodgen/e_floods.htm
Read about newsworthy flood events in our watershed.
Critical Flood Depth and Velocity (River and Stream Systems)
The following table outlines the CRITICAL depths and velocities that will harm people and structures. These criteria define the "floodway", which identifies an area of unacceptable risk where development and site alteration is prohibited. In general, a one zone policy is applied where the entire floodplain is considered the floodway and all development is prohibited. Only where special policies, administrative capacity and suitable conditions are in place can the following approach be used. (Technical Guide - River and Stream Systems: Flooding Hazard Limit, Ontario Ministry of Natural Resources, 2002)
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Depth (threat to life)
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In stagnant backwater areas (zero velocity), depths in excess of about 1m are sufficient to float young children, and depths above 1.4m are sufficient to float teenage children and many adults. |
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Velocity (threat to life)
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Relatively low velocity can pose possible flood hazards. Velocity effects are better understood when used in combination with depth. |
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Depth and Velocity
(threat to life)
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The hazards of depth and velocity are closely linked as they combine to effect instability through an upward buoyant force, a lateral force and unbalanced hydrostatic forces…A product of less than or equal to 0.4m2/s defines a low hazard provided the depth does not exceed 0.8m and the velocity does not exceed 1.7m/s. |
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Duration of Flood
(Length of time in the overbanks)
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Any floodproofing measures proposed must be able to withstand the forces for the required length of time. |
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Rate of Rise and Fall
(Time to react, type of floodproofing)
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Rate should be considered where the stability of the soil or slope would be affected by rapid drawdown or where the time to implement flood measures in not sufficient |
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Vehicular access
(emergency access)
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Most automobiles will be halted by flood depths above 0.3-0.5m. A maximum flood velocity of 3m/s would be permissible, providing that flood depths are less than 0.3m. A depth of 0.9-1.2m is the maximum depth for rapid access of large emergency vehicles.(note: interviews with local agencies indicate a much lower threshold) |
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Impact Loading and Debris Accumulation
(threat to life and property)
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Sites where the potential for ice or debris loading should simply be avoided or sites should be designed to intercept or deflect materials |
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Structural Integrity
(structures below ground)
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Any hydrostatic head in excess of 0.2m may result in damage to basement floors. (NOTE: basement construction is generally prohibited when in or in close proximity to the floodplain) |
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Structural Integrity
(structures above ground)
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A depth of 0.8m is the safe upper limit for the above ground/super structure of conventional brick veneer, and certain types of concrete block buildings. The structural integrity of elevated structures is more a function of flood velocities (eg. Erosion of foundations, footings or fill) than depth. The maximum permissible velocity depends on soil type, vegetation cover and slope but ranges between 0.8-1.5m/s |
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Fill (stability)
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In general, fill may become susceptible to erosion/instability at depths of 1.8-2.4m |
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