GEOMORPHIC ANALYSIS OF PALEOSHORELINES IN HORRY COUNTY, SOUTH CAROLINA: 1967 VERSUS 2018

In the study we compare the results of previous geomorphological studies and the techniques used in Horry County, South Carolina to our results using modern digital elevation data sets, aerial imagery, and Geographic Information Systems (GIS). We supplement these results with recent, detailed 1:24,000-scale geological field mapping to add geological context to these geomorphological models.

The Horry Barrier System, was first described as the “Horry Cape” by Johnson and DuBar (1964). It consists of a series of roughly east-west trending, slightly curved sand ridges that are sub-parallel to the modern coastline, with younger ridge-sets truncating older sets. The system extends from the North Carolina state line westward to the Pee Dee River valley. At its greatest length the system is 46 km long and ranges in width from 6-24 km.

Thom (1967) produced detailed geomorphology, beach ridges, swales, and scarps, of the Horry Barrier System from available aerial photography and topographic maps. DuBar and others (1974) mapped a larger area and added more detail by further subdividing the system into additional, younger sub-barriers within the larger barrier system.

Using modern mapping technology (i.e. LiDAR data, true- and false-color aerial imagery, GIS, ) we revisit the geomorphological interpretations, compare and contrast the two generations of maps, and, with the addition of our new borehole logs and detailed geological maps, propose an explanation for the current course of the Little Pee Dee River. While it has been noted that the barrier system prograded seaward with the addition of younger beach ridges seaward of old ridges (DuBar and others, 1974), through our new mapping and imaging methods we propose that due to westward long-shore drift, the system grew laterally until it diverted the mouth of the Little Pee Dee River, with each new seaward beach ridge elongating and widening westward as the sand ridges infilled the river valley.