The first week
of July will mark the ten-year anniversary of Tropical Storm Alberto's
devastating floods in Georgia. Areas of west Georgia were particularly
hard hit, with three-day rainfall amounts in excess of 21 inches producing
over $750 million in damage and contributing to 33 deaths.
Tropical Storm Alberto originated in Senegal, near the west coast
of Africa, on June 18, 1994 as a tropical wave. The system became Tropical
Depression One on June 30, 1994. On July 2, 1994 the depression
strengthened in the Gulf of Mexico near the Yucatan Peninsula to become
Tropical Storm Alberto. When the center made landfall near Destin,
Florida, on July 3, Alberto was at its peak intensity with 65 mph winds.
Alberto quickly weakened to a tropical depression again. After landfall,
the motion of the storm slowed and precipitation increased. The storm
moved slowly through Alabama into Georgia, stalling just south of Atlanta.
Over the next few days it reversed its course and then looped back on its
previous course before ultimately dissipating.
During the period
of July 3-6 of 1994, Alberto dumped copious amounts of rain across the
area. The heaviest rainfall was south of a Carrollton to Atlanta line and
west of an Atlanta to Macon to Cordele line. The greatest rainfall in
Middle Georgia fell in a band from Peachtree City south to Americus.
Rainfall amounts of 12 to 24 inches were common in this stretch. Rainfall
amounts as high as 21.1 inches in 24 hours were observed at Americus,
Georgia with storm totals at Americus of 27.61 inches.
This
rainfall produced record and near-record flooding along the Flint,
Ocmulgee and Chattahoochee Rivers. In Middle Georgia, the worst-hit cities
were Macon and Montezuma. In Macon, parts of downtown were flooded and the
water supply was lost for many days as flooding inundated the water plant.
In Montezuma, flood waters topped the levee and flooded much of downtown.
Overall, flash flooding and flooding caused by the rainfall from Alberto
took 33 lives, destroyed thousands of homes, including entire communities,
forced approximately 50,000 people to be evacuated, and caused property
damage estimated at $750 million. Approximately two-thirds of the deaths
were related to vehicular incidents.
The Weather Forecast Offices
and the Southeast River Forecast Center of the National Weather Service
(NWS) played critical roles in getting the word out to the record crests
that were expected. Peak flood stages from Alberto in the NWS Peachtree
City's area of responsibility were:
River Location Alberto Record (feet) Old Record (feet)
Flint Culloden 45.73 38.40 (3/5/1929)
Flint Montezuma 34.11 27.40 (3/17/1929)
Ocmulgee Macon 35.30 29.83 (3/19/1990)
Ocmulgee Hawkinsville 40.91 36.50 (1/21/1925)
Ocmulgee Abbeville 23.10 20.30 (1/23/1925)
Ocmulgee Lumber City 24.59 26.30 (1/21/1925)
The Advance
Hydrologic Prediction Service is the NWS's frontline solution to provide
improved river and flood forecasting and water information across the
United States. AHPS builds upon the NWS's long history of around-the-clock
forecasting excellence by bridging to new sciences and technologies. AHPS
includes state-of-the-science forecasting tools covering flash floods on
small streams to long-range forecasts for floods in larger rivers. AHPS
can be seen on our website by going to weather.gov and clicking on
Georgia. Select "Lakes&Rivers – AHPS" on the left menu.
The
Site Specific Model is a hydrologic model run at local NWS offices. This
model allows local NWS offices to improve forecasts on smaller streams and
creeks mainly associated with flash floods or shorter-duration floods. The
NWS office in Peachtree City is leading the way with over a dozen specific
forecast points now provided. New sites are being added when needed by
local communities. Recently, for example, a new forecast point was added
to the Etowah River near Dawsonville, Georgia at the request of Forsyth
County emergency management officials.
Multi-sensor rainfall is
now being used to produce many of the hydrologic forecasts in Georgia. In
the past, the NWS either rainfall from rain gauges alone or from radar
estimates. Today, we combine rainfall estimates from the NWS WSR-88D radar
with rainfall gauge data provided by NWS observers and automated NWS and
USGS sites. This high-quality rainfall estimate from multiple sources is
being used by our Site Specific Model in Georgia.
Another tool
added to our flood detection arsenal is called the Flash Flood Monitoring
Program. This tool allows local NWS meteorologists and hydrologists to get
a better handle on flash floods. This tool combines high resolution
rainfall estimates from the WSR-88D Doppler radar with small hydrologic
basins in Georgia. The result is the ability to issue flash flood warnings
for counties, and naming specific creeks that will be affected. In
addition, this tool allows for earlier and better detection of floods by
keeping forecasters alert to fast changes within individual creeks. The
benefits of this were seen during the 2003 floods in Georgia. Prior to
2003, the NWS in Peachtree City detected 70% of flash floods with a false
alarm rate around 50%. In 2003, our detection of flash floods improved to
about 80% while our false alarm rate dropped to 20% due, in large part, to
the new technologies.
The last tool for NWS meteorologists and
hydrologists to use is called the hydrologic forecast system. This tool
allows forecasters to be alerted whenever a river or stream is approaching
flood stage. In the past, flood warnings were issued by doing a lot of
typing. Now, we can issue these warnings quickly because most of the work
is done by our high technology computer systems.
Finally, the
National Weather Service has launched a campaign called, "Turn Around
Don't Drown (TADD)". This is to discourage citizens who see flooded
roadways or bridges from crossing them. It is better to turn around and
take a different and safer route.
Since flooding is the number one
storm-related killer, the NWS is committed to continued improvements to
detection of floods and flash floods.
For additional
hydrologic questions, call Jim Noel, Senior Hydrologist with the NWS in
Peachtree City at 770-486-1133.
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