An outflow event on the left side of Hurricane Harvey: Erosion of barrier sand and seaward transport through Aransas Pass, Texas

Storm surge is a critical component in the evolution of barrier island systems, eroding the shoreface and depositing sediment landward as overwash deposits; this “rollover” process enables barrier islands to migrate landward during periods of rising sea level. However, cyclonic storms may also generate seaward-directed flow and sediment transport, which is not typically accounted for in barrier island modeling. A strong outflow occurred at Port Aransas, Texas during Hurricane Harvey in 2017, as evidenced from field observations, satellite photos, and tide data; modeling indicates that outflow was forced by offshore winds to the left of landfall. To investigate the impact of this event on the barrier system, we collected post-storm multibeam bathymetry data and sediment samples within Aransas Pass and Lydia Ann Channel, important conduits linking the bays to the Gulf of Mexico, and where such data were previously collected in 2009 and 2012. The 2009–2012 comparison provides a baseline against which to ascertain the storm impact contained in the 2012–2017 comparison. Both land- and marine-based evidence indicate that significant erosion accompanied the outflow event, focused at the edges of the Corpus Christi ship channel and Lydia Ann Channel. Large quantities of sand, up to 6.5 m thick, also accumulate in deeps of Aransas Pass and Lydia Ann Channel, presumably as the outflow event waned in strength. We infer that the outflow event transported a large amount of barrier system sands offshore, but do not have sufficient constraints at this time to quantify it.