| Cahaba River | |
| Subdivision Type1: | Country |
| Subdivision Name1: | United States |
| Subdivision Type2: | State |
| Subdivision Name2: | Alabama |
| Subdivision Type3: | County |
| Length: | 194miles |
| Source1 Location: | Jefferson County, Alabama |
| Source1 Coordinates: | 33.6875°N -86.6°W |
| Mouth: | Alabama River |
| Mouth Location: | Dallas County, Alabama |
| Mouth Coordinates: | 32.3192°N -87.0947°W |
| Progression: | Alabama → Mobile → Gulf of Mexico |
| Basin Size: | 1870sqmi |
| Tributaries Left: | (numerous) |
| Tributaries Right: | (numerous) |
The Cahaba River is the longest substantially free-flowing river in Alabama and is among the most scenic and biologically diverse rivers in the United States.[1] It is a major tributary of the Alabama River and part of the larger Mobile River basin. With headwaters near Birmingham, the Cahaba flows southwest, then at Heiberger turns southeast and joins the Alabama River at the ghost town and former Alabama capital of Cahaba in Dallas County. Entirely within central Alabama, the Cahaba River is long[2] and drains an area of . The name Cahaba is derived from the Choctaw words oka meaning "water" and aba meaning "above"[3]
The Cahaba River flows across three physiographic provinces of the state: Appalachian Plateau, Ridge and Valley, and Coastal Plain.[4] The Mobile River basin has the largest Gulf Coast drainage basin east of the Mississippi River, and the Cahaba is one of the seven river systems that contribute to its flow. The mean discharge of water from 1938 to 2000 is about 80 m3/s. The average rainfall is 138 cm/yr. The terrestrial biome of the river is classified as eastern deciduous forest.
The Cahaba River begins in the Valley and Ridge region bounded by the Piedmont to the southeast and the Cumberland Plateau to the northwest. It has two major physical regions: Upper and Lower Cahaba. The river empties into the Alabama River. The upper Cahaba forms roughly the first 100 miles, starting at the headwaters and continuing to the Fall Line, a region in which the Appalachian Mountains end and the Gulf Coastal Plain begins. It passes through Trussville, Leeds, Irondale, Birmingham, Mountain Brook, Hoover, Vestavia, Helena, West Blocton, and Centreville. The lower Cahaba begins at the fall line and continues through Selma and empties into the Alabama River at the former town of Cahaba.[5] [6]
Located adjacent to the Cahaba River basin, the Moundville Archaeological Site (1000–1450 AD) was the second-largest community of the Mississippian culture. The Black Warrior River and the Cahaba River run parallel to each other for over 100 miles, often as close as 30 miles apart. The Bottle Creek Site (1250–1550 AD), located little more than 100 miles downriver in the Mobile-Tensaw River Delta, also influenced the region. A large mound remains on the river, just south of Centerville. A large village occupied the town of Cahaba site from 100 to 1550 AD, during the Woodland and Mississippian periods.
See main article: Cahaba, Alabama. The Cahaba River ends at the former town of Cahaba, also known as Cahawba, or Old Cahawba.[6] The town of Cahaba was Alabama's first seat of government from 1820 to 1825. William Wyatt Bibb, Alabama's first governor, decided on Cahaba because of the scenery, fertile area, and navigable river ways. Cahaba suffered harsh economic struggles and disease from 1819 to 1822. However, in 1821, a steamboat, the Harriet, overcame the Alabama River's fast current and made it past Cahaba. The river became a major trade route, which caused the city to grow, despite the removal of the capital to Tuscaloosa in 1825. Cahaba is now an abandoned town and a state historical site, administered by the Alabama Historical Commission.[6]
The Ridge and Valley region of Alabama, which is where the Cahaba River begins, was formed when the African Plate collided with the North American Plate in the Paleozoic era. The valley soils consist of gravel, sand, and clay, while the ridges consist of chert and sandstone. The upper Cahaba region contains Cenozoic-era gravel, clay, and sand. In the lower Cahaba region, the soils are calcareous, or chalky.[7]
The waters of the Cahaba are home to more than 131 species of freshwater fishes (18 of which have been found in no other river system), 40 species of mussels, and 35 species of snails. The river has more fish species than can be found in all bodies of water in California.[8] Sixty-nine of these animal species are endangered. The endemic freshwater snail Elimia cahawbensis is named after the river. One species long thought to be extinct, Leptoxis compacta, the Oblong rocksnail, was rediscovered in the Cahaba in 2011.[9] Due to damming for hydropower, pollution, transportation, and erosion, it has suffered losses of species. Almost a quarter of the original documented mussel species in the Cahaba have disappeared with similar trends in the fish and snail numbers of species. Many species have still been discovered and rediscovered in and on the surrounding region of the river. The Cahaba is also home to 13 snail species not found anywhere else in the world. In the early 21st century, a Georgia botanist Jim Allison discovered eight unknown flower species, and later eight more were identified along the river's course that previously had not been sited in the state of Alabama. This region is most noted for containing numerous species of mollusks and snails. These species feed other aquatic dwelling animals, improve water quality by eating algae, and even indicate environmental issues due to their receptiveness of pollution. Fourteen of the freshwater fish species are non-native species in the Cahaba River.
Among the countless plant species that thrive in and around the Cahaba is Hymenocallis coronaria, known in Alabama as the Cahaba lily. As a result of its abundant presence here and its threatened status in the three states where it is found, a portion of the Cahaba River near West Blocton has been designated as the Cahaba River National Wildlife Refuge.[10] [11] It is found only in South Carolina, Georgia, and Alabama. While this flower once was present through all of the Southeast, it now exists in about 70 stands with a fourth of the stands in the Cahaba River. The seeds travel with the river's flow, and crevices in the shoals (rocky bars that run across the river) shelter the seeds as they sprout. The Cahaba lilies bloom in early May, and the entire blooming season is through by mid-June.[12] The flowers open in the evening instead of the day due to pollination by sphinx moths, which are active at night.[5] Each flower blooms and lasts only one day before wilting.
There are numerous small tributaries, including:
The Cahaba flows through heavily populated areas in the Birmingham metropolitan area. It serves as the source of drinking water in the upper course for over 1 million people and is also a popular canoeing destination.
A number of Alabama cities lie on the banks of or in close proximity to the river. They include: