What Do Floodwaters Do

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What Do Floodwaters Do?

• What happens to everything floodwaters touch or
  saturate?
• Your car?
• The bottom of a mobile home?
• How would you describe the smell?
• What happens to water quality?

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A Floodplain Is

• a. River or stream channel up to natural banks
• b. Low-lying area along a river, stream, or coast
  subject to flooding
• c. Area along a river, stream, or coast subject
  to flooding by the 1 chance flood
• d. Area along a river, stream, or coast that is
  developed and subject to flooding

Which of these definitions apply?
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Why Are People in Floodplains?

• First settlers faced a wilderness without roads.
• Coasts and rivers provided harbors,
  transportation routes, and fishing/water sources.
• Now people enjoy living near water for recreation
  and pleasant surroundings.
• Unintended consequence Flood losses.

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We love our streams
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We hate our streams
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STREAM CHANNEL
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WHAT DO STREAMS DO?

• Collect water from the watershed
• Convey varying amounts of water
• Dissipate energy
• Transport and redistribute sediment
• Seek dynamic equilibrium
• Change in response to changing conditions

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WATERSHED
A watershed is an area of land from which
surface and subsurface waters drain to a
common receiving body or outlet.
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Watershed Processes

• Rainfall intensity and duration
• Steepness or slope
• Size or area
• Land cover
• Ability of ground cover to absorb water
• Obstructions along watercourses (e.g., culverts,
  bridges, etc.) that impede flow

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FLOW PATHS
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Watershed Changes Over Time
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URBANIZATION
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URBANIZATION
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DYNAMIC EQUILIBRIUM

• Dynamic equilibrium means that the stream moves
  and adjusts in such a way as to minimize the
  energy of the system. The change is what makes
  the equilibrium dynamic.

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CHANNEL STRAIGHTENING
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What Do Floodplains Do for Us?

• Naturally store and convey floodwaters.
• Maintain water quality.
• Recharge groundwater aquifers and naturally
  regulate flows into rivers and lakes.
• Support large and diverse populations of plants
  and animals.
• Provide historical, scientific, recreational,
  and economic benefits to communities.

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Altering Natural Floodplains

• Damages or destroys fish and wildlife breeding,
  nursery, and feeding grounds.
• Robs downstream habitats of nutrients.
• Threatens a significant percentage of endangered
  species.
• Only 20-30 of U.S. Floodplains
  remain undisturbed.

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MANAGING STREAMS
ten thousand river commissions, with the mines
of the world at their back, cannot tame that
lawless stream, cannot curb it or define it,
cannot say to it Go here, or Go there, and
make it obey cannot save a shore which it has
sentenced, cannot bar its path with an
obstruction which it will not tear down, dance
over, and laugh at. --Mark Twain, Life on the
Mississippi
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No Adverse Impact Floodplain

• Action by one property owner/community does not
  increase flood risks for other properties/communit
  ies.

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No Adverse Impact

• Initiative of the ASFPM.
• Communities within a watershed cooperate.
• Action by one property owner/community does not
  increase risk of others.
• ASFPM Web site www.floods.org
• Other resources Your States NFIP State
  Coordinating Office, State ASFPM Associations

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Thanks To

• Association of State Floodplain Managers
  (http//www.flood.org)
• NYS Floodplain and Stormwater Managers
  Association (http//ny.floods.org)
• Chemung County Soil and Water Conservation
  District (http//www.chemungcountyswcd.com)
• See Stream Guide