By: Tania, Mariam

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• By Tania, Mariam Marvin

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What is a Flood

• A flood is
• A general and temporary condition of partial or
  complete inundation of two or more acres of
  normally dry land area or of two or more
  properties from
• Overflow of inland or tidal waters,
• Unusual and rapid accumulation or runoff of
  surface waters from any source, or
• A mudflow.

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What is a Drought

•  A drought is defined as "a period of abnormally
  dry weather sufficiently prolonged for the lack
  of water to cause serious hydrologic imbalance in
  the affected area."
• In easier terms, a drought is a period of
  unusually persistent dry weather that persists
  long enough to cause serious problems such as
  crop damage and/or water supply shortages. The
  severity of the drought depends upon the degree
  of moisture deficiency, the duration, and the
  size of the affected area.

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How do Floods Form

• A number of factors can contribute to that
  imbalance, including
• heavy, intense rainfall
• run-off from a deep snow cover
• over-saturated soil, when the ground can't hold
  anymore water.
• frozen soil
• high river, stream or reservoir levels caused by
  unusually large amounts of rain
• ice jams in rivers
• urbanization, or lots of buildings and parking
  lots

• The collapse or subsidence of land along the
  shore of a lake or similar body of water as a
  result of erosion or undermining caused by waves
  or currents of water exceeding anticipated
  cyclical levels that result in a flood."
• Water circulates from clouds to the soil to
  streams to rivers to the oceans and then returns
  to the clouds. When that system backs-up there is
  a flood.

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How Do Droughts Form

• When no rain or only a very small amount of rain
  falls, soils can dry out and plants can die. When
  rainfall is less than normal for several weeks,
  months, or years, the flow of streams and rivers
  declines, water levels in lakes and reservoirs
  fall, and the depth to water in wells increases.

• If dry weather persists and water-supply problems
  develop, the dry period can become a drought.

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Time of the Year

• FLOODS
•   Can occur any time of the year. Occur usually
  in the spring season due to ice and snow melting
  and frequent storms .
•   In some countries there are monsoon seasons, a
  time of great rain, when floods often occur.
• DROUGHTS
• - In Regions with warmer winters where the soil
  water does not freeze, a drought may occur during
  any season.
• -In general, droughts present the greatest threat
  from March through September for most North
  America.

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Where Floods Occur

•   Floods occur all over the world except for
  Antarctica
•   Usually occur urban areas where water cannot
  drain into the soil properly
•  They usually affect floodplains, low lying,
  flat areas near large bodies of water
• Highlands are least likely to have a flood

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Where Droughts Occur

•   Humid areas have short term droughts arid
  regions have long term.
•  Usually around the 30 degree latitude where
  there is dry, cool air.
•   Example, Africa, Asia Kenya, Ethiopia,
  Somalia.
• Droughts usually occur in hot dry areas of land.
  In most cases the area is dry because there is
  very minimal rainfall. The rain that does fall
  will be quickly absorbed into the ground or blown
  away by the dry air flow that moves along the
  ground. Therefore the land is very dry and not
  many things can live there.

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Factors of Weather

• Floods are formed mostly by heavy rainfall.
• The heavy rain fall can cause banks or soil to
  collapse causing flooding.
• Droughts are formed by not having enough rain
  fall, drying out the soil.
• So the two opposites, a drought and flood, both
  depend on the same thing, rain.

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Frequency

• FLOODS Floods occur much more frequently than
  droughts, although they can come at any season,
  floods are at a higher risk of occurring during
  the Spring.
• DROUGHTS Droughts occur less frequently than
  floods, but there are high chances of them
  occurring after March in the spring, or after a
  dry winter.

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Car Driving Through Flooded Water

• Water weighs 62.4 lbs. per cubic foot and
  typically flows downstream at 6 to 12 miles per
  hour.
• When a vehicle stalls in the water, the water's
  momentum is transferred to the car. For each foot
  the water rises, 500 lbs. of lateral force is
  applied to the automobile..

• But the biggest factor is buoyancy. For each foot
  the water rises up the side of the car, the car
  displaces 1500 lbs. of water. In effect, the
  automobile weighs 1500 lbs. less for each foot
  the water rises.
• Two feet of water will carry away most
  automobiles!!!

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Events In Our Area

• In our area, on July 1989, and intense thunder
  storm contributed to 450 mm of rain over Harrow
  and much of Essex County. The intensity of the
  flooding was greatly reduced due to the regions
  flat topography. The total damage estimate was
  between 44-55 million dollars, due to the damage
  to infrastructure, buildings and content, and
  crops.

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Recent Examples

• FLOODS New Years day on January, 1997, there
  were heavy snowstorms followed by warm weather,
  causing fast melting of ice, and 36 people were
  killed, and 65,000 in California were evacuated.
  Highways were washed out or blocked by
  landslides. In Reno, Nevada, the casinos were
  closed for the first time while Yosemite National
  Park was so hard it that it closed for months.
  The total damage was 3 billion dollars.

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Potential for Destruction Droughts

• Droughts can kill livestock, crops, and in
  extreme cases, people can die of thirst if the
  dried up bodies of water are their only source of
  water.

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Potential For Destruction Floods

• Floods can also kill livestock, damage buildings,
  destroy personal belongings, infrastructure, and
  it can cause deaths of those who cannot get to
  higher ground or escape.

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THE END

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