EVIDENCE FOR QUATERNARY CHANNEL INCISION AND MIGRATION OF THE CATAWBA RIVER NEAR CHARLOTTE, NC

The timing and mechanics of down-cutting rivers in the southeastern Piedmont could provide insight into external forces, such as climate, that impact river evolution. In order to constrain the Quaternary history of a down-cutting river, we have examined evidence for incision, lateral migration and oxbow formation along the Catawba River near Charlotte, NC. Based on point bar, scroll bar and channel morphologies visible in aerial imagery and LIDAR, the Catawba River has recently undergone a channel straightening event which included both meander neck and chute cutoff processes. This interpretation is supported by both core and ground penetrating radar observations which document the geometry and extent of laterally extensive basal erosion surfaces, ~9m thick point bar deposits, channel cut banks, lateral accretion bedding, scroll bar and swale deposits, and oxbow lakes and channel fills. Grain size and plant distributions are consistent with this interpretation. The recent channel straightening suggests that the Catawba River is currently migrating laterally and reworking its valley floor deposits rather than incising. Earlier periods of incision are recorded by abandoned fluvial terraces at higher elevations on the valley walls. According to Layzell et al., (2009) there are 5 strath terraces (with estimated ages) situated at 3 m (4 kyr), 10 m (50 kyr), 14 m (128 kyr), 28 m (610 kyr), and 41 m (1470 kyr) above the current river level. The cobble beds that mark the bases of the upper 3 terraces are probably stable landscape elements as indicated by the oxidized weathering haloes that are consistently thicker on the bottom sides of the cobbles. The upper terraces are characterized by populations of larger cobbles, suggesting greater competence and discharge of the paleo-Catawba River as compared to today.