Quantitative Geomorphology of the Congaree River Throughout the Last Century

The Congaree River is an 80 km, single thread river in central South Carolina. Here we present the analysis of a hydrographic survey, field data, aerial photos and LiDAR data to quantify spatial and temporal changes in the geomorphology of the Congaree over the last 140 years. In particular, we use data collected between 1884 and 2022. In this period the Congaree watershed has experienced urbanization, deforestation, and the construction of a dam on one of the two main Congaree River tributaries. Despite these changes, channel migration rates, slope, and width were found to not change in time, although they varied spatially in relation to the floodplain's bank erodibility. Twenty-three recent cross sections were surveyed to quantify and compare the geometry, hydraulics, and sediment transport capacity of the channel over time. Results indicate that channel geometry did not change significantly in the bedrock reach of the river, but the downstream part of the Congaree saw a reduction in bankfull depth and channel width. Calculations of sediment transport capacity show that the channel has mobilized the same sediment sizes for the past 140 years.