Page 339 - Laboratory Manual in Physical Geology

F. Most homeowners insurance policies do not insure against floods, even though floods cause more damage than any other natural

hazard. Homeowners must obtain private or federal flood insurance in addition to their base homeowners policy. The National
Flood Insurance Program (NFIP), a Division of the Federal Emergency Management Agency (FEMA), helps communities develop
corrective and preventative measures for reducing future flood damage. The program centers on floodplain identification, mapping,
and management. In return, members of these communities are eligible for discounts on federal flood insurance. The rates are
determined on the basis of a community’s FIRM (Flood Insurance Rate Map), an official map of the community on which FEMA
has delineated flood hazard areas and risk premium zones (with discount rates). The hazard areas on a FIRM are defined on a base
flood elevation (BFE)—the computed elevation to which flood water is estimated to rise during a base flood. The regulatory-standard
base flood elevation is the 100-year flood elevation. Based on your graph, what is the BFE for Montezuma, GA?
Flood Data Table

Recurrence Intervals for Selected, Ranked, Annual Highest Stages of the Flint River over 99 Years of
Observation (1897 and 1905–2002) at Montezuma, Georgia (USGS Station 02349500, data from USGS)
Rank of annual Year River elevation Gage elevation River elevation Recurrence Probability of Percent chance
highest river (*n = 99) above gage, above sea above sea interval** occurring in of occurring in
stage (S) in feet level, in feet level, in feet (RI), in years any given year any given year***
1 (highest) 1994 34.11 255.83 289.9 1 in 100 1%
2 1929 27.40 255.83 283.2 1 in 50 2%
3 1990 26.05 255.83 281.9 1 in 33.3 3%
4 1897 26.00 255.83 281.8 1 in 25 4%
5 1949 25.20 255.83 281.0 1 in 20 5%
20 1928 21.30 255.83 277.1 5.0 1 in 5 20%
30 1912 20.60 255.83 276.4 3.4 1 in 3.4 29%
40 1959 19.30 255.83 275.1 2.3 1 in 2.3 43%
50 1960 18.50 255.83 274.3 2.0 1 in 2 50%
60 1934 17.70 255.83 273.5 1.8 1 in 1.8 56%
70 1974 17.25 255.83 273.1 1.5 1 in 1.5 67%
80 1967 14.76 255.83 270.6 1.3 1 in 1.3 77%
90 1907 13.00 255.83 268.8 1.1 1 in 1.1 91%
99 (lowest) 2002 8.99 255.83 264.7 1.0 1 in 1 100%
*n = number of years of annual observations = 99
**Recurrence Interval (RI) = (n + 1) / S = average number of years between occurrences of an event of this magnitude or greater.
***Percent chance of occurrence = 1 / RI x 100.
10-year flood 100-year flood 1000-year flood
320

Flood Magnitude: River Elevation in Feet above Sea Level
310

300

290

280

270

260
1 2 3 4 5 6 7 8 9 10 20 30 40 50 100 200 400 1000
Flood Frequency: Recurrence Interval (RI)
309