Reading: From Reservoir to Wetland: the Rise and Fall of an
Ohio Dam; Evans & others in The Earth Around Us.
At least some of us drive by flood control devices everyday and
have little idea we have done so. For this exercise, identify
and describe 3 specific flood control devices/sites in the Omaha
area, with at least two different types of devices (i.e. two may
be the same type, but different examples/sites). Find out what
agency or group is responsible for building or managing them.
If you can, find out how much they cost.
is the need?" or some case histories of flooding.
1965 South Platte, near Denver, Colorado.
- associated with intense local rain, flash
flood with debris flow aspects.
- local resident "The banks of the creek
disappeared as if the land was made of sugar."
- many bridges taken out.
- industrial corridor hit the worst, $508,000,000
damages, 6 fatalities.
- floodplain has been rebuilt since then.
1972 Rapid Creek, Rapid City, South Dakota:
Historic Floods on the Missouri River - DNR website.
March, 1993, Platte River Flood - slides.
Many, many more examples. Floods are one of
the largest losses for the insurance industry.
Some links to explore more.
What determines how much water a channel can accommodate?
- measured as discharge, volume per
unit time, e.g. gallons per minute.
- discharge = velocity * cross section area
= ft/sec * ft-squared/sec = ft-cubed/sec = volume/time
- factors in model for channel flow:
- channel cross section profile.
- bottom roughness.
- water viscosity.
- overbank = flood.
What determines discharge amounts?
- rainfall and/or snowmelt input
- evaporative and riparian vegetative losses.
- groundwater loss or gain
- drainage basin characteristics:
- what is the drainage basin?
- what characteristics will be important for
determining how much water it supplies downstream?
- type of vegetative cover.
- surface seepage characteristics.
- what human activities can change drainage
Hydrographs - a basic tool for looking at discharge
- definition - plot of discharge with time
for a given channel section.
- shows very rich complex behavior.
- area under a section of the curve is volume.
- form a function of rainfall input, groundwater
supply, of drainage basin characteristics.
- change of hydrograph form downstream for
a storm event - curve widens and diminishes.
- some examples showing seasonal fluctuations
and distinct flood events. Free from the USGS!
Surface water management tools:
- bank protection.
For each of these one can ask, in a given situation,
how cost effective they are.
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