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CHAPTER 1
BACKGROUND AND OVERVIEW OF THE EVENT


1.1 INTRODUCTION

A decaying tropical system, previously known as Tropical Storm Alberto, produced torrential rainfall which resulted in some of the worst flooding ever observed across portions of the States of Georgia, Alabama, and Florida during July 1994. Alberto, the 1994 Atlantic Hurricane Season's first named tropical system, came ashore near the Florida Panhandle town of Destin at about 1500 Universal Coordinated Time (UTC) on July 3. The winds associated with the tropical storm caused only minor damage and no casualties, as maximum sustained winds of around 65 mph (55 knots) were briefly observed at the time of landfall. The highest storm surge was estimated at 5 feet near the point of landfall (Destin, Florida). No reports of tornadoes were confirmed in association with Alberto or its remnants.

As the tropical storm's winds rapidly diminished, attention was quickly and appropriately turned to the threat of heavy rainfall associated with the deep tropical moisture being transported by the remnants of Alberto. Indeed, over the course of the 4 days following landfall, the forward motion of the remnants of Alberto slowed and halted, only to loop back over the same area already traversed before finally dissipating. It was this meandering motion which resulted in record-breaking rainfall, including a storm total of over 27 inches at Americus, Georgia, more than 21 inches of which fell in a 24-hour period. The torrential rainfall led to exceptional flooding across central and western Georgia, southeastern Alabama, and the Florida Panhandle. Five river basins were particularly hard hit (see Figure 1-1 ): (1) the Flint River Basin in western Georgia, (2) the Ocmulgee River Basin in central Georgia, (3) the Chattahoochee River Basin along the Georgia-Alabama state line, (4) the Choctawhatchee River Basin in Alabama, and (5) the Apalachicola River Basin in Florida.

1.2 IMPACT OF THE FLOODING

Figure 1-2 shows the counties that were Presidentially declared disaster areas. Most of the declared counties were concentrated along the five rivers (and their tributaries) mentioned in the section above. A total of 78 counties were declared Federal disaster areas, including 55 in Georgia, 10 in Alabama, and 13 in Florida.

The flooding took a significant toll on human life, as a total of 33 persons perished. Of that total, 31 deaths occurred in Georgia, while the other 2 occurred in Alabama. Many of the fatalities, as is typical with flood events, occurred as a result of flash flooding; and most occurred in vehicles. In addition, approximately 50,000 people were forced from their homes due to the flooding. More than 18,000 dwellings were damaged or destroyed by the floods, and nearly 12,000 people applied for emergency housing. In Macon, Georgia, the fresh water supply to nearly 160,000 people was disrupted when the water treatment plant, located along the banks of the Ocmulgee River, was flooded. Some residences were without fresh water for as long as 19 days. In addition, thousands of people and pieces of equipment were engaged in various flood-fighting efforts throughout the three-state area impacted by the flooding. Dozens of Federal, state, and local government agencies, private organizations, as well as various volunteer groups, were heavily involved in the massive mobilization of resources. Federal agency participation included, but was not limited to, the Federal Emergency Management Agency (FEMA) , U.S. Army, U.S. Army Corps of Engineers, U.S. Department of Transportation, U.S. Department of Housing and Urban Development, and Small Business Administration.

With respect to property damages, the estimates are nearly $750 million across the States of Georgia, Alabama, and Florida as a result of this flood event. In addition to the more than 18,000 dwellings damaged or destroyed, hundreds of bridges and well over 1,000 roads sustained damages. Also, 218 dams (most of them small dams located in Georgia) were damaged by the flooding, many of which failed altogether. Agricultural losses accounted for approximately $100 million. In the States of Georgia, Alabama, and Florida combined, more than 900,000 acres of crops were affected by the flooding. Georgia and Alabama suffered the greatest crop losses with more than 400,000 acres in each state impacted. In all three states, peanuts and cotton were the commodities most severely affected. Livestock losses were also significant, especially to poultry, with as many as 250,000 chickens reportedly lost to the flooding.

1.3 HYDROMETEOROLOGICAL ANALYSIS

While Tropical Storm Alberto will not likely be remembered for its wind nor its storm surge, it most certainly will be remembered, especially amongst Georgians, for its rainfall and flooding. The following sections describe, in some detail, the tropical weather system that was Alberto, from its origin as a tropical wave over western Africa to its dissipation as a tropical depression over central Alabama.

1.3.1 STORM GENESIS AND LANDFALL

The tropical weather system which would eventually become Alberto was first detected as a tropical wave over western Africa on Saturday, June 18. Moving on a westerly course, the wave traversed the tropical Atlantic Ocean uneventfully until it neared the Virgin Islands when some increase in thunderstorm activity occurred. However, thunderstorm activity diminished 2 days later when the wave neared the Bahamas.

The wave continued moving westward and, on June 29, moved across Cuba where thunder- storm activity rapidly increased; and a very weak circulation became evident. With the system located in the vicinity of the western tip of Cuba, a National Oceanic and Atmospheric Administration (NOAA) reconnaissance aircraft was sent to investigate the disturbed weather area. Based on the information obtained from that flight, NOAA's National Hurricane Center proclaimed the system the 1994 Atlantic Hurricane Season's first tropical depression on June 30 (see Figure 1-3 for Alberto's track). Still moving westward, the poorly organized depression cleared Cuba then took a turn to the northwest into the Gulf of Mexico where it became better organized. Reconnaissance aircraft data indicated that the depression then strengthened to a tropical storm at approximately 0000 UTC, July 2, at which time the system was named Tropical Storm Alberto.

Alberto then began to track northward towards the Florida Panhandle as it continued to gradually intensify. Peak intensity was reached just prior to landfall when Alberto's sustained winds were 60-65 mph (55 knots), and the central pressure of the storm was near 993 millibars (mb). Alberto's center made landfall near the town of Destin, Florida, at 1500 UTC on Sunday, July 3, approximately 39 hours after becoming a tropical storm. On Sunday evening (0000 UTC July 4), just a few hours after landfall, the storm was down- graded to a tropical depression. For the next 2 days after landfall, the remnants of Alberto moved north-northeastward at a progressively slower forward speed, eventually coming to a halt near Atlanta, Georgia, on July 5. The remnants of Alberto then began to backtrack, moving westward into east-central and then central Alabama. The system dissipated during the evening hours of Thursday, July 7, over central Alabama.

1.3.2 DESCRIPTION OF THE ANTECEDENT CONDITIONS AND HEAVY PRECIPITATION

With respect to the antecedent conditions prior to Alberto's arrival, much of the spring of 1994 was quite dry throughout the Southeast. In fact, many southeastern residents were undoubtedly concerned about recurring drought conditions, similar to those which occurred during the summer of 1993. However, June 1994 brought much wetter conditions over most of the Southeast. In fact, the rainfall in June resulted in some localized flash flooding and even some limited, mostly minor river flooding across portions of the Southeast. At the beginning of June, moderate-to-extreme drought conditions existed across a considerable portion of the Southeast, especially over Georgia and South Carolina. But due to the wet June, by the time of Alberto's arrival in early July, hydrologic conditions across much of the Southeast had returned to near normal, or just slightly drier than normal. Thus, the wet June certainly was a factor in the evolution of the July flood.

There is little question as to the cause of the torrential rainfall associated with Alberto and its remnants. While heavy precipitation accompanies nearly every tropical system, excessive rainfall was produced by the remnants of Alberto due to two main factors: (1) the slow, forward motion of the system and (2) the meandering, looping (retrogressive) nature of the system's track. These characteristics contributed to rainfall accumulations that, in several places, exceeded 20 inches. Noteworthy was Americus, Georgia, which received a storm total of 27.61 inches (July 3-9), including a 24-hour total of 21.1 inches (July 5-6). While such amounts are certainly not unprecedented, they are nonetheless rare, even with decaying tropical systems.

Figure 1-4 shows the National Weather Service (NWS) Climate Analysis Center's storm total isohyetal analysis. The heaviest rains (16 inches or greater) fell in a relatively narrow band across southwestern Georgia and southeastern Alabama. Some of the worst flash and urban flooding occurred in this excessive rainfall area, as evidenced by the 15 fatalities that occurred in the vicinity of Americus, Georgia. In contrast, a far larger area was inundated with 8 or more inches of rainfall. It was this heavy precipitation that fell over a fairly large area that generated tremendous runoff and resulted in the widespread river flooding.

1.3.3 DESCRIPTION OF THE FLOODING

Figure 1-5 is a composite figure combining portions of Figures 1-1 through 1-4. This figure shows the inland track of Alberto and its remnants, the area enveloped by the 8-inch rainfall isohyet, the major rivers affected by flooding, and the counties that were Presidentially declared disaster areas.

As is typical with flood events of this magnitude, widespread major river flooding evolves from flooding which first manifests itself in the form of urban, small stream, and flash flooding. Such was the case with this flood. The first reports of flooding included flooded roads, underpasses, culverts, and the like. Since the heaviest rains were generally close to the path of the center of Alberto, the pattern of flooding essentially followed the path of the storm center. Thus, flooding first broke out across portions of the Florida Panhandle and southeast Alabama, then across southwestern portions of Georgia. Flooding later broke out across much of the remainder of western and central Georgia. As rainfall persisted and soils became saturated, small streams and rivers began to overflow; and small dams were threatened by the tremendous inflow into the reservoirs behind them. Some small, unregu- lated earthen dams began to fail, and reports of road and bridge washouts became common.

Within a day after landfall, the forward motion of Alberto slowed. The rains continued, and some of the larger rivers began to approach flood stage at various locations. Late on July 5, with the center of Alberto coming to a halt near Atlanta, portions of numerous large rivers exceeded flood stage; and river flooding became more widespread and significant. By the morning of July 6, some locations had observed record flooding; and the first crests began to appear along some of the smaller rivers and at some upstream locations along the larger rivers. Alberto's movement became erratic--the system was now moving westward, looping back over a portion of its previous track. Additional rainfall caused a progression in flooding from urban and small stream flooding to river flooding. By July 7, as Alberto's center drifted into central Alabama, rainfall finally diminished, both in intensity and in areal coverage. Tremendous volumes of water were now moving down major river systems in portions of Georgia, Alabama, and Florida: the Flint, Ocmulgee, Chattahoochee, Choctawhatchee, and the Apalachicola Rivers. River flooding peaked, both in terms of coverage and severity, during the period July 6-15; but flooding would continue along portions of some rivers until close to the end of July.

By far, the worst flooding occurred along Georgia's Flint and Ocmulgee Rivers and their tributaries. Some of the hardest hit cities along these rivers include Albany, Macon, and Montezuma. Across the entire three-state area impacted by the flooding, 17 NWS river forecast locations set new record flood stages, some breaking the old record by 5-7 feet. In all, 47 NWS river forecast locations exceeded flood stage. Crests of 5-15 feet above flood stage were common, while portions of some rivers observed crests that exceeded flood stage by more than 20 feet. The NWS offices involved in the flood event across the three-state area issued 657 watches, warnings, and statements related to the event; and the Southeast River Forecast Center (SERFC) issued 238 NWS internal river forecasts.

River Graphic

Figure 1-1 Major river basins impacted by flooding in July 1994 as a result of Alberto: Flint, Ocmulgee, Chattahoochee, Choctawatchee, and Apalachicola River Basins.

River Graphic

Figure 1-2. A total of 78 counties were declared Federal disaster areas: 55 in Georgia, 10 in Alabama, and 13 in Florida.

River Graphic

Figure 1-3. Alberto's track, July 1994.

River Graphic

Figure 1-4. Storm total precipitation during the period July 3-9, 1994 (Americus, GA: 27.61" storm total).

River Graphic

Figure 1-5. Composite showing Alberto's inland track (dashed line), the 8-inch isohyet, the 78 counties declared Federal disaster areas (shaded), and the five major river systems.




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