RESPONSE OF THE LOWER SANTEE RIVER SYSTEM TO THE CONSTRUCTION OF THE PINOPOLIS AND SANTEE DAMS

The Santee River Delta is located on the coastal plain of central South Carolina. It is the second largest river on the eastern US coast, with its headwaters in the Appalachian Mountains of North Carolina. This river system has been modified extensively in the past; however, the Santee has largely remained void of modern infrastructure and development. The first wave of modification occurred during the 1800s where 150 sqkm of lowland Cyprus forest swamp were cleared for rice cultivation. The second wave came in the 1940s where the Pinopolis and Santee dams were constructed to create the two largest hydro-electric lakes. These dams divert a large portion of the flow away from the Santee River and act as the new basins for sediment deposition, thus significantly altering and reducing the natural sediment transport processes down to the coast and the original ocean-facing delta.

This study investigates the changes in river bottom structure related to the dam construction. This goal was achieved through the acquisition of new bathymetric data in comparison with a digitized bathymetric map from 1934. In addition, characterization of bedforms and their systematic distribution, shallow seismo-acoustic data and sediment grain size analysis were explored for an in-depth look at the modern hydrodynamic conditions of the lower Santee system.

There seems to be a definitive location in the seismo-acoustic data where the two Santee River branches switch from fluvial-dominance with many major morpho-sedimentary bedforms towards a deltaic control which is dominated by smoother bottom structures with minor bedforms. Utilizing the pre-dam and post-dam bathymetric data, grids were subtracted from each other to determine locations of possible lateral, depth, and also geometric changes in river course structure. Additionally, a lateral shift after the dam construction in the location of the transition zone could reflect a shift in the dominance of the fluvial regime.