Alabama Landscapes

Piedmont

River Systems

Three main river systems drain the Piedmont: the Coosa, Tallapoosa and Chattahoochee

 The Coosa River System

The drainage basin of the Coosa River and its tributaries includes portions of the Northern Piedmont upland district.  It includes some 5,350 sq. miles in Alabama

Figure PR1 Drainage pattern of the Coosa River. (Pattern from Alabama Water Watch)

The Coosa enters the Piedmont from the Valley and Ridge section north of Lay Lake dam and exits at Wetumpka where it joins the Tallapoosa to become the Alabama River.   Three dams were built on the Coosa in the Piedmont (the Bouldin, Jordan and Lay) to generate hydroelectricity.  Mean annual discharge at Jordan Dam is about 16,400 cu ft/sec.
 

The main trunk of the Coosa in the Piedmont flows generally in a south-southeasterly direction and is relatively straight, particularly when compared with its meandering channel pattern in the Coosa Valley district of the Valley and Ridge.  Sinuosity south of Mitchell dam is 1.1, amplitude is 0.7 miles and wavelength 3.4 miles. It cuts across the regional grain of the rocks of the  Talladega and Ashland- Wedowee Belts. 

Tallapoosa River System

Over 50% of Alabama’s Piedmont is drained by the Tallapoosa River and its tributaries (Figure PR2).  The main trunk of the system is about 200 miles long, entering the state near Muscadine in Cleburne County and leaving the Piedmont at Tallassee (Tallapoosa County).  The system drains about 3,300 square miles.

Figure PR2. Drainage pattern of the Tallapoosa River and its tributaries. (Pattern from Alabama Water Watch)

On a regional scale, the Tallapoosa and Little Tallapoosa Rivers are a series of relatively straight segments that show abrupt changes in direction in a rectangular drainage pattern.  The dominant flow directions are southwesterly, southerly and westerly.  The most abrupt change occurs near Belltown (Cleburne County) where the Tallapoosa changes direction from southwest to south.  These prominent changes in direction suggest an underlying geologic control (perhaps large fractures) on course of the river.

 On a local scale, the Tallapoosa system is characterized by meandering stream channels.  However, there is a distinct difference in the types of meanders. The difference can be seen in Randolph County (Figure PR3).

 Figure PR3. Drainage pattern of the Tallapoosa River and tributaries, Randolph County Alabama (Base map from Cartography Research Lab., University of Alabama)

Northeast of L.R. Harris Dam the Little Tallapoosa displays closely spaced, extremely sinuous meanders often with ridges up to 100 feet above the river separating parallel loops.  Sinuosity is about 3 along the Little Tallapoosa,  and amplitude is 0.7 miles and wavelength 1.2 miles.  Similar meanders occur along Wedowee Creek and in the Tallapoosa River near Muscadine.  Elsewhere, the rivers have the more common form of meanders, larger, not as sinuous and display shapes similar to a sine curve in trigonometry.  The Tallapoosa south of Harris dam has a sinuosity of about 1.4.   Amplitude is 1.3 miles  and wavelength is about 4 miles

Floodplains vary in width from less than 50 feet to over one mile. The streams have incised up to 400 feet into the plateau, particularly in the Northern Piedmont. 

 A longitudinal profile along the main trunk of the Tallapoosa River (Figure PR4) shows a uniform gradient of about 3.4 ft/mile from the Alabama-Georgia Border to the upper reaches of Lake Martin.  Downstream, gradient increases to over 4 ft/mile as the river leaves the Piedmont and flows onto the Coastal Plain at the Fall Line.

Figure PR4. Longitudinal Profile along the Tallapoosa River.  (Source ADEM.) 

 The increased gradient at the Fall Line coupled with narrow and deep V-shaped valleys led Alabama Power to construct a series of hydroelectricity dams along the Tallapoosa.  Martin (1926), Yates (1928) and Thurlow (1930) dams were completed before World War II.  Harris Dam, built over rapids 77 miles upstream from Martin Dam, was completed in 1983.   

Annual discharge is estimated to be about 4,770 cu ft/sec at Horseshoe Bend.

The Chattahoochee River System 

Streams in the eastern portion of the Southern Piedmont flow easterly to drain into the Chattahoochee River.

Figure PR5.  Drainage pattern of the Chattahoochee River system in Alabama. (Pattern from Alabama Water Watch)

Sinuosity is 1.4 south of Lanett, with 5 meander curves in 10 miles and amplitude of 2.7 miles (crest to trough) and wavelength of 4 miles.

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