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river basins of georgia

ALTAMAHA RIVER BASIN
By Gretchen Loeffler and Judy L. Meyer

The Altamaha River Basin includes the Ocmulgee, Oconee (Figure 1), and Altamaha Rivers (Figure 2). A major continental divide occurs between the Ocmulgee and Flint Rivers, which causes the Altamaha River Basin to drain into the Atlantic Ocean. This river basin is the largest watershed in the state of Georgia and the third largest in the U.S. draining into the Atlantic Ocean. The headwaters of the Oconee and Ocmulgee Rivers originate in the foothills of the Appalachians and meet to form the Altamaha River in the Coastal Plain region of Georgia. Atlanta, Macon, and Lumber City are three major metropolitan areas along Ocmulgee River. Along the Oconee River, Athens is located in the headwater region, and Milledgeville and Dublin are located in the middle and southern reaches of the river. Further downstream of the confluence between the Ocmulgee and the Oconee Rivers, the Ohoopee River, a black-water tributary, joins the Altamaha. A total of 137 river miles marks the distance between the convergence of the Oconee and Ocmulgee Rivers and the entry of the Altamaha into the Atlantic Ocean near Darien, Georgia. The tidal estuary at the mouth of the Altamaha functions as a linkage between the freshwater habitats of the river basin with the salt-water system of the Atlantic Ocean. During the 1800's, the Altamaha River was a major route for shipping to the Georgia coast.

Figure 1. Oconee River.

Figure 2. Altamaha River.

Stream Flow
The following table lists stream flow data for the Ocmulgee, Oconee, and Altamaha Rivers. The locations of the U.S. Geological Survey gauging stations are denoted within the parentheses. Note the differences in drainage area and flow rate for these three rivers.

Table 1. Stream flow data from USGS. Stream flow is measured in units of cubic feet per second (cfs) flowing past a point.

Protected species
Over 100 rare and endangered aquatic species are found in the Altamaha. The watershed provides habitats for nesting and breeding migratory birds as well as common game species. In 1991, the Nature Conservancy initiated an ecological survey to assess the biological resources and potential threats to the integrity of freshwater species diversity in the Altamaha River. This fragile watershed sustains 11 imperiled pearly mussel species, seven of which are found nowhere else in the world.

Land Use/Population
Land use activities within a watershed have a direct impact on the health of streams and rivers. In the Altamaha River Basin, agriculture dominates the landscape. The headwaters of the Ocmulgee River begin in the highly urbanized Atlanta metropolitan area, and downstream its watershed is dominated by agriculture and forested areas. The Oconee River headwaters arise in a highly forested region, but the presence of agriculture increases as the Oconee flows southeastward towards the Altamaha River. The 90-mile long coastal flood plain of the Altamaha River is covered with dense timber and underbrush. The Altamaha River watershed includes about 2.5% of Georgia's total area, but only 0.7% of the state's total population.

Impoundments in the Altamaha River Basin
The National Dam Inventory documents 276 dams in the Upper Oconee River watershed, while a detailed scale analysis found more than 5,400 impoundments in the watershed (Merrill 2001). These figures demonstrate that the majority of the reservoirs in this watershed are unaccounted for and their environmental impacts can be underestimated. Two large dams (greater than 25 feet high) were built along the mainstem of the Oconee River. The two reservoirs formed from the construction of these impoundments are Lake Sinclair and Lake Oconee. Neither the Ocmulgee nor the Altamaha Rivers have large dams built along their mainstems.

Groundwater
Three distinct groundwater aquifers influence the Altamaha River Basin. In the northern headwaters, crystalline-rock aquifers dominate. In the lower reaches of the Oconee and Ocmulgee Rivers, cretaceous aquifer systems lie beneath the surface. The Altamaha River is part of the large Floridan aquifer system. Groundwater aquifers that occur near the fall line are exposed or close to the surface. South of the fall line, which includes the Altamaha River, the majority of domestic water supplies come from groundwater sources.

Figure 3. Land use and land cover in the Altamaha River Basin. Black stars denote approximate locations of the USGS gauging stations referenced in Table 1. Source: Georgia Rivers LMER.

Land cover and land use patterns
Table 2 lists the 1998 land cover percentages for the Ocmulgee, Oconee, and Altamaha River basins. The Natural Resources Spatial Analysis Laboratory (NARSAL) at the University of Georgia provided the tabular data.

Table 2. 1998 land cover statistics

Impaired Waters
The upper reaches of both the Oconee and Ocmulgee Rivers are in the top 10% of Georgia's most impacted watersheds. The sources of these pollutants are a combination of urban runoff, storm sewers, municipal point sources, and combined sewer outflows.
Only 6% of the sampled surface waters in the Altamaha River watershed have reported problems according to state and EPA data. Nonpoint source pollution in the watershed contributes to organic enrichment, metals contamination, and fish consumption advisories in the Altamaha and its tidal estuarine system.

Additional information and sources

Hodler, T.W. 1986. The atlas of Georgia. Institute of Community and Area Development: University of Georgia, Athens.

Merrill, M.D. 2001. Local and watershed influences on stream fish biotic integrity in the Upper Oconee watershed, Georgia, USA. Thesis (M.S.): University of Georgia.

USGS gauging stations

Nature Conservancy (Altamaha River)

Environmental Defense Fund (watershed pollution)

Environmental, Educational, and Community Action Organizations

American Rivers

Georgia Adopt-A-Stream

Georgia Canoeing Association

Georgia River Network

River Network

Nature Conservancy of Georgia

Trust for Public Land

Altamaha Riverkeeper

Summit to the Sea

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