Summary of Significant Floods in the United States, Puerto Rico, and the Virgin Islands, 1970 Through 1989

Georgia is located in the southeastern United States and is bordered on the southeast by the Atlantic Ocean. The Atlantic Ocean and the Gulf of Mexico are the primary sources of moisture for the State. Georgia's climate is also affected by the distance from the ocean and elevation, as northern Georgia is in part of the Appalachian Mountains. Annual precipitation, which varies greatly from year to year, averages about 44 in. in the east-central part of the State and about 76 in. in the highest mountains in extreme northeast Georgia (Paulson and others, 1991). The summers are characterized by warm, humid maritime airmasses that are pushed inland by a nearly stationary subtropical Atlantic high-pressure cell called the Bermuda High. Airmass and squall-line type thunderstorms can create localized torrential downpours and flash flooding. Late summer and fall brings the threat of Atlantic Ocean and Gulf of Mexico hurricanes and associated coastal flooding from storm surges and excessive rainfall. Winters in Georgia typically include frontal systems moving through or stalling out in the State. Significant flooding can occur anytime during the year.

On the basis of regionalization procedures that relate flood characteristics to watershed and climatic characteristics, the magnitude of maximum discharges for streams in Georgia is dependent upon physiographic region and the drainage area. The regions include the mountainous area of the north, the rolling piedmont to the southeast, and the fall-line region, which bisects the State and is a 10- to 50-mi wide band between the piedmont and the low-relief coastal plain. For urban areas, the percentage area of impervious surface in the drainage basin is an added factor.

The deadliest flood in Georgia from 1970 through 1989 occurred in November 1977 when excessive rains in the Toccoa Creek Basin in northeastern Georgia resulted in the failure of the Kelley Barnes Dam. The resulting flash flood killed 39 persons and caused $2.8 million in damages (Paulson and others, 1991). Significant flooding also occurred statewide in the spring of 1973, when about 13 percent of the State's streamflow-gaging stations recorded significant discharges. In March 1976, about 7 percent of the gaging stations statewide recorded 20-year or greater recurrence-interval discharges. During 1979, widespread flooding occurred during March and April predominately in eight counties in the northern part of the State. Recurrence intervals were generally in the 10- to 20-year range, with some smaller streams having 50-year recurrence-interval flooding.

Paulson, R.W., Chase, E.B., Roberts, R.S., and Moody, D.W., compilers, 1991, National water summary, 1988-89-Hydrologic events and floods and droughts: U.S. Geological Survey Water-Supply Paper 2375, 591 p.