VOCAB GHC Ch 13: Floods Flashcards
Regional floods
Huge, long-lasting floods in large river valleys with low topography resulting from prolonged heavy rains over an extensive region. They cause heavy economic losses.
Flash Flood
A local and sudden flood of relatively great volume and high velocity that lasts for a short time following a few hours of intense rainfall. Flash floods cause many deaths.
Gradient
The slope of a stream channel bottom; change in elevation divided by distance. Gradient increases with steeper slope.
Base level
The lowest point to which a stream or river can flow, often referred to as the ‘mouth’ of the river; usually sea level.
Equilibrium
A state of balance in a system; a condition in which opposing processes are so balanced that changes cause compensating actions.
Discharge
The volume of water flowing in a stream per-unit of time.
Sinuosity
The length of a stream channel divided by the straight-line distance between its ends.
Load
The amount of material moved and carried by a stream.
Meander
The curves, bends, loops, and turns in the course of an underloaded stream that shifts its bank erosion from side to side of its channel.
Braided stream
And overloaded stream so full of sediment that water flow is forced to divide and recombine in a braided pattern.
Graded stream
An equilibrium stream with an evenly sloping bottom adjusted to efficiently handle water flow (discharge) and sediment (load) transport.
Floodplains
The nearly flat lowlands that border a stream and act as the stream bed (the physical confine of the normal water flow) during floods.
Feedback
A change in the system that provokes further changes.
Positive feedback
Occurs in nonequilibrium systems where one changed triggers more changes in the same direction. The vicious cycle.
Negative feedback
Occurs in equilibrium systems where one change triggers another change that tends to negate the initial change and restores equilibrium. Example: when too much water pours into a channel, increased erosion lowers the gradient to slow the water flow and maintain equilibrium.
Recurrence intervals
The average time interval between floods or earthquakes of a given size.
Avulsion
The abrupt change in the course of the stream and the adoption of a new channel.
Levees
A natural or human built embankment along the side of the stream channel.
Floodway
River channels and adjacent lowlands reserved to handle floodwater diverted from a large river.
Flood stage
Water level at which a river overflows it’s banks and levees.
Hydrograph
A plot of water volume, height, flow rate, etc., with respect to time.
Riprap
Large, irregular boulders placed to slow the attack of erosion.
What are key variables in how streams work?
Discharge, available setiment, gradient, and sinuosity.
What is the relationship of discharge and load?
The greater the discharge, the greater the load of sediment carried.
What factors cause a river to come out of equilibrium?
Too much discharge or too much load.
What are lakes, in a geologic sense?
Temporary features that streams are striving to eliminate.
Florence, Italy, 1333 and 1966
River Arno flooded 633 years after it flooded in 1333, to the day. Flowed through the city at 6.2 m depth. Burst open drums of oil.
What is the relationship between the size and recurrence time of a flood?
The larger the floods, the longer the recurrence times between each.
What phenomena unleash killer floods?
A local thundercloud can form and unleash a flash flood in just a few hours, abundant rainfall lasting for days can cause regional floods that last for weeks, the storm surges of tropical cyclones flood the coasts, the breakup of winter ice on rivers can pile up and temporarily block the water flow, hot weather can cause rapid melting of snow, short-lived natural dams fail and unleash floods, human-built dams and levees fail.
Distinguish between flash floods and regional floods.
A typical flash flood results when rain falls intensely for hours in a small area. Regional floods occur when lots of rain falls over a large area for days or weeks.
Most flood related deaths are caused by what type of flood?
Flash flood
In the U.S., how much of the land is floodplain? This land is home to how much of the population?
2.5%, 6.5%
What has become a significant problem posed by the Mississippi River’s desire to change course?
The river has long wanted to avulse toward the Atchafalaya River, but is being forced to continue down the Mississippi by the U.S. Army Corps of Engineers. They want the river to continue flowing through the major cities of Baton Rouge and New Orleans.
Action stage
Water begins overtopping the banks.
Minor flood stage
Roads, parks, and yards may be covered by water.
Moderate flood stage
Building inundation occurs; roads are closed and evacuations may be necessary.
Major flood stage
Buildings may be completely submerged; lives are threatened and large-scale evacuations may be necessary.
Slow motion disaster
Insidious disasters
Name some structural responses to floods.
Dams, levees, engineering projects, and sandbagging
Name some nonstructural responses to floods.
More accurate flood forecasting, zoning and land-use policies, insurance programs, evacuation planning, and education.
What is channelization? What problems does it pose?
It is the attempt to control floodwaters by clearing channels of debris, and making them deeper, wider, and straighter. This creates huge discharge and destroys the habitat.
How are desert floods different from normal floods?
Most of the damage of desert floods is due to bank erosion, not inundation.
What is the largest-scale problem posed by ice-dam failure floods?
The discharge of cold, low-salinity glacial meltwater could change the circulation of deep water through the world ocean, changing global climate.
