Geology Reference
In-Depth Information
Refer to Figure
8.23
in Chapter
8,
Athens, Ohio.
6.
Shade on this map (1975), the area of the Hocking River
floodplain from the Fairgrounds to the Radio Tower.
works be installed or removed, or should the status of
development change with population growth, FIRMs
may quickly become outdated.
For example, if an area upstream from a site
along a river is changed from forest to urban, the
amount of water that runs off (goes rapidly to streams
rather than soaking into the ground or being used by
plants) increases dramatically. In wooded or rural
areas, typically 5-30 percent of the rainfall runs off,
while in business and industrial areas, 50-90 percent
of the water runs off and in residential areas 25-70 per-
cent of the water runs off. The amount of runoff will
also depend on other factors such as the density of
development in an area, the types of soils, the angle of
hillslopes, and the intensity and duration of individual
storms. In general, however, development leads to a
2-3 times increase in the amount of runoff (Iowa
Department of Transportation, 2004).
7.
Are any buildings located on the floodplain? Identify three
of the major ones.
8.
What has happened to the course of the river through time
in the area south of the sewage disposal facility?
Flood Insurance Rate Maps
In 1968, Congress created the National Flood Insurance
Program. Flood Insurance Rate Maps (FIRMs) are
part of this program. According to the FEMA website
(
http://www.fema.gov/pdf/
fh
m/ot_frmsb.pdf), flood
information on FIRMs is based on historic, meteorologi-
cal, hydrologic, and hydraulic data, as well as the
amount and types of open space, the existence or absence
of flood control works, and the status of development.
FIRM are used to determine if homeowners need to
obtain flood insurance. It is less expensive to own a home
if you do not have to pay for flood insurance.
It is important to note that FIRMs represent a
"snapshot" in time, as they reflect the conditions in
existence at the time of the creation of the map. Should
weather patterns change, perhaps as local or regional
manifestations of global climate change, should the
amount of open space change, should flood control
Washington, DC
Figure 10.15 is a FIRM map of part of Washington, DC. The
left side of the map is the Potomac River. Rock Creek flows
into the Potomac from the east. The circular "Zone C" on the
east side of the river is centered on the Lincoln Memorial.
9.
Let's first look at the background (nonflood) information
on the map. What types of background data are shown on
the map?
10. What types of background data are missing from the map
that would be helpful in identifying flood hazards?
