QUATERNARY EVOLUTION OF AN INCISING PIEDMONT RIVER: THE CATAWBA RIVER NEAR CHARLOTTE, NC

The long-term evolution of down-cutting rivers in eastern North America is of widespread interest. We have examined Quaternary incision, lateral migration, oxbow sedimentation and a chronosquence of soils developing in terraces of the Catawba River in the vicinity of Charlotte, NC. The Catawba River is a single channel, meandering river that drains 8556 square km from its headwaters on the Blue Ridge escarpment, through the Piedmont of North and South Carolina to the Coastal Plain. The river currently is controlled by a series of dams and reservoirs. Downstream of Cowans Ford dam there is a free-flowing stretch where the Catawba River and its adjacent valley are characterized by steep valley walls, 5 fluvial terraces, and several oxbow lakes produced by channel straightening, the timing and cause of which remain uncertain. Coring, ground penetrating radar and air photo data indicate that during its most recent history, the Catawba River migrated laterally and produced a widespread basal erosion surface carved into bedrock, ~9 m thick point bars, and scroll bar and swale deposits. Once the channel was abandoned, the oxbow lakes filled with fine-grained sediments, became emergent and vegetated, and then cultivated. Backwater effects associated with the damming of the Catawba River have flooded the formerly emergent farmland. Pollen analyses from oxbow lake samples document abundant pine, oak and ragweed as well as corn, cotton, hemlock, fungal debris and charcoal suggesting that this alluvial environment was dominated by input from both a weedy, fire-prone nearby upland and Piedmont sources. The 5 terrace deposits each are characterized by distinctive morphology, soil development and basal quartz pebble conglomerates. Tentative ages are assigned to the terraces by comparison to regional terrace elevation/age curves. The elevations (and inferred ages) of the 5 terraces are: 3 m (4 kyr), 10 m (50 kyr), 14 m (128 kyr), 28 m (610 kyr) and 41 m (1,470 kyr) above the modern river yielding incision rates ranging from 0.02 to 0.61 mm/yr which increase progressively through time.