Geology Reference
In-Depth Information
100-year flood?
monetary flood loss (in billions of dollars) for each decade.
What is the general trend in flood loss in the United States
between 1900 and 2000 as determined from Table 10.2 and
your graph?
7.
Either find someone who has plotted the second set of
data for your stream, or repeat steps 1 through 7 to deter-
mine the predicted discharge for a 100-year flood, using the
second set of data for your stream. (You may plot the second
set of data on Figure 10.1; note that depending on your
choice of numbers for the first plot, you may need to have a
second set of values on the vertical axis.) How does your
prediction made in Question 6 compare with the answer
from the other set of data for the river you plotted?
13.
Now place an open circle for each decade to show the
U.S. population in millions of people at the end of each
decade.
14. a.
For flood damage losses in the 20th century in Figure
10.2, describe and explain the trend.
b.
What is the role, if any, of growth in population and ris-
ing flood losses in the 20th century?
8.
Suggest possible human activities in the watershed that
could have caused the differences in predicted floods that
result from the two sets of data.
c.
What other factors contribute to increased losses?
9.
When you have completed interpretation of the stream
you selected, find students who have done the other stream.
How do their data compare with yours? What human activi-
ties did they suggest for the changes in flood predictions
they discovered?
15.
Discuss the effectiveness of flood mitigation in the 20th
century with your lab group. Are flood control systems
effective?
10.
Based on the flood predictions for all four data sets, what
does the contrast in predicted flood discharges imply about
the usefulness of the 100-year flood as a legal designation for
these two streams?
16.
According to the Corps of Engineers (2000), for the
decade of the 1990s, the average damage loss per year was
about $5 billion. For the same period the average value of
flood damage reduction by projects per year is estimated at
$20 billion. Using this information and that in the graphs
you plotted discuss the statement "Flood-control dams and
levees have been effective in reducing flood damage" and
suggest additional measures for reducing flood damage.
11.
What information do you need to know if you are about
to buy a house that is located adjacent to, but just outside of,
the 100-year floodplain?
The Discharge/Area Ratio
Questions 17 and 18 investigate ranges in flood discharge
(Q) with drainage basin size (A) for several different sizes of
rivers. This flood intensity comparison is based on data in
Table 10
.3,
which will be plotted in Figure 10
.3.
Large Floods in the United States
Data in Table 10.2, partly from the U.S. Army Corps of Engi-
neers, show the damages suffered and deaths due to flood-
ing. The U.S. Army Corps of Engineers (2000) provides data
on
damages avoided
by flood projects and by emergency
activities of the Corps. For example, in 1999 flood projects
reduced potential damages by $2.8 billion (75% by reservoirs
and 25% by levees), while emergency activities of sandbag-
ging and technical assistance saved $48 million in losses, a
much smaller amount.
Do Questions 12-16, which refer to Table 10.2.
17.
Use the flood records in Table 10
.3
to calculate the dis-
charge/ area ratio for each river. Record your calculation in
the column on the table. Plot the calculated ratio against
drainage-basin area in Figure 10
.3.
Identify the six rivers that
you are able to plot.
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