The formation of this inlet suggests a prolonged period of back-barrier flooding until a low point in the barrier was breached during the Holocene sea-level highstand of 1.5 m. BP, a new tidal inlet formed to the north of Lake Makhawulani, where impounded waters were diverted via a low point in the back-barrier coastal dune cordon. Along-strike variation in the timing of the basin infilling, attributed to changes to the inlet functioning coupled to the segmentation of the waterbody, is characteristic of this area. BP, coeval with the formation of the prograding marginal spits and waterbody segmentation (Unit C2). Recalibrated AMS dates place the system closure to between 31 cal. The deposition of Unit E signifies the closure of the system to the ocean and the overall shift from an estuarine/lagoon environment to a lacustrine one. Unit E caps the stratigraphy and is interpreted as lacustrine fines with a thin layer of acoustically transparent material (gyttja) on top. The unusual depth of Surface T-RS is attributed to (1) limited sediment supply during sea-level rise, (2) the presence of easily erodible fine sediments in which this surface erodes and (3) a larger tidal prism when the Bhanga Nek inlet was still open and system segmentation by Units C2 and D had not yet occurred. Unit C2 spits are in turn associated with slump deposits formed on the steepest part of the margins (Unit D) that were dated to 2900 ± 165 cal. These are separated by an erosional surface (T-RS) formed by migrating tidal channels as sea-level rose and marine waters entered the system during the Holocene. Two forms of prograding spits are evident ̶Unit C1 progrades from the palaeo-highs of the valley interfluves into the nearest available accommodation space and Unit C2 progrades from the margins of the system into the basin. Unit B forms as thickly developed central basin deposits, partially infilling the incised valleys. A major unconformity surface (SB), characterised by broad u-shaped incised valleys, incises the underlying unconsolidated sandy acoustic basement (Unit A). A total of 5 seismic units were imaged (Units A-E). In this context, two cores were extracted from the system (KB2 and KB4), together with over 150 km of seismic reflection profiling, as well as AMS radiocarbon analyses and legacy data in order to present a new stratigraphic evolution model for this back-barrier system. The location of this system behind a continuous coastal barrier predisposes it to excellent archives of environmental change related to changing sea-level and sediment supply. Formerly, the system's only connection to the ocean was through the Bhanga Nek palaeo-inlet. The Kosi Bay system comprises four interconnected lakes (Lake Makhawulani, Lake Mpungwini, Lake Nhlange and Lake Amanzimnyama) subject to varying degrees of marine influence. This study examines both the inlet dynamics, recorded in the back-barrier stratigraphy of Kosi Bay, and the competing effects of waterbody segmentation on along-strike changes in the character and nature of an incised valley fill at Kosi Bay, South Africa. in: America's Most Vulnerable Coastal Communities, eds., Kelley, J.T., Pilkey, O.H., and Cooper, J.A.G.,: As the coastal system responds to ongoing processes of rising sea level and storm dynamics, efforts to engineer fi xes are increasing and now constitute a "human hurricane" that pits conventional utilization of the barriers against the natu- ral coastal system dynamics that maintain barrier-island integrity over the long term. The ongo- ing natural processes have escalated efforts to stabilize these dynamic islands and associated inlet in time and space by utilizing massive rock jetties and revetments, kilometers of sand bags and constructed dune ridges, and extensive beach nourish- ment projects. With construction of coastal Highway 12 on Bodie and Pea Islands (1952) and the Oregon Inlet bridge (1962-1963), this coastal segment has become a critical link for the Outer Banks econ- omy and eight beach communities that occur from Rodanthe to Ocracoke. The inlet was opened in 1846 by a hurricane and subsequently migrated 3.95 km past its present location by 1989. Bodie and Pea Islands evolved as classic inlet- and overwash-dominated (transgressive) simple barrier islands that are now separated by Oregon Inlet. Pea Island extends 19.3 km from the southern shore of Oregon Inlet to Rodanthe Vil- lage and is the Pea Island National Wildlife Refuge. Bodie Island extends for 15 km from the Nags Head-Kitty Hawk urban area to the north shore of Oregon Inlet and is part of Cape Hatteras National Seashore. Pea Island, Oregon Inlet, and Bodie Island, North Carolina, are severely human- modifi ed barrier-island segments that are central to an age-old controversy pitting natural barrier-island dynamics against the economic development of coastal North Carolina.
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