MORPHODYNAMICS OF CAPTAIN SAMS INLET AND KIAWAH SPIT, 1989-2016

Captain Sams Inlet is a migrating ebb tidal inlet located along the central mesotidal South Carolina coast between Kiawah and Seabrook Islands. Historical images and beach surveying were used to quantitatively measure channel migration and barrier island geomorphic variability for the years 1989-2016. Southwest channel migration, channel pivot, and net spit growth were consistent throughout the study except during two engineered breachings in 1996 and 2015. Migration averaged 44 m/year, pivot was 1.8 degrees/yr and areal increase was ~20,736 m²/year during the 1999-2015 natural growth period. Although total spit area and length consistently increased, the spit’s neck area and width decreased at rates of 610 m²/yr and 1.3 m/yr, respectively. The neck is along the Kiawah River cut bank which has eroded the spit’s backbarrier at the neck 3.1 m/yr since 1989, while the cut bank’s arc area has increased an average of 2386 m²/year. Elevation profiles indicate the spit neck’s highest dune in 2016 (5.7 m) would have been overwashed by Hurricane Hugo’s 1989 6.1 m storm surge, while the narrowest part of the neck measured only 3.5 m and is well below Hugo’s storm surge. Continued erosion behind the spit neck, combined with the high potential for storm breaching indicate that Kiawah Spit and Captain Sams Inlet comprise a highly variable and unstable system that is expected to continue its 355 year historic migration and natural breaching cycle.