Rivers and Flooding Flashcards
Discharge is measured by multiplying the _____ by the ______.
average water velocity: area of the water in the channel
How can the potential for flooding be reduced without reducing discharge?
increase velocity by
- increase slope (S)
- increase channel efficiency (R)
- decrease sinuosity
- reduce roughness coefficient (n)
One way to increase the slope of a stream channel is to
decrease sinuosity
Lateral migration of a meandering stream results in _______.
decrease in slope
increase in sinuosity
The geological process of ______ happens at point bars.
Deposition
_____ are evidence for lateral migration.
meander scrolls
process that occurs at cutbank side of a stream
erosion
How does urbanization affect flooding?
decreases lag time while increasing peak discharge
The probability of a 50 year flood occuring next years is?
2%
What is the probability of a 100 year flood occuring the next year?
1%
rainfall is gentle favors _______.
infiltration
soil is porous and sandy favors ______.
Infiltration
ground is nearly saturated favors ______.
runoff
surface lacks vegetation and is barren favors ______.
runoff
What is the plot of discharge or stage and time called?
hydrograph
The boundary that separates one drainage basin from another is known as:
drainage divide
In hydrograph the maximum discharge corresponds to ______.
flood peak
The formation of a meander cutoff results in a(n) _____ in sinuosity
decrease
The layers of fluids in an oil trap is controlled by ______.
density
cap rocks have ____ permeability and _____ porosity
low, low
Greenhouse effect is caused by the ______.
absorption and rerdiation of outgoing, long wavelength, radiation by greenhouse gases (CO2)
A ____ channel has a smaller hydraulic radius than a _____ channel.
wide and shallow : semicircular
In Manning’s equation, n measures ______.
the resistance to flow at the bottom of a channel
In Manning’s equation R is _____.
a measure of the efficiency of a channel cross section
Slope is calculated by dividing _____ by ______.
vertical drop of channel’s end points : length of channel
Lateral migration of a meandering stream results in a(n) ____ in sinuosity.
increase
feature that results from meander cutoff
oxbow lake
feature that results from lateral migration of the stream
meander scrolls
How do you calculate hydraulic radius (R)?
R=A/P
A = area of water in channel
P= wetted perimeter of channel
Three ways to increase velocity of water in a channel.
- decrease resistance to flow (n)
- increase channel efficiency (R)
- increase slope (S)
wide, shallow channel has ____ R.
low
A semicircular channel has _____ R.
high
Sinuosity is _____ divided by ______.
channel distance / linear distance
urbanization ______ lag time.
decreases
urbanization _____ discharge.
increases
what equation gives you averge water velocity in a channel?
Manning’s equation
Slope is ______ divided by ______.
vertical drop of the channel’s end points, length of channel
exceedance probability is
the probability (p) of an event of a particular magnitude being equaled or exceeded any given year.
What is reccurence interval
average number of years between events of similar or greater magnitude
