Sea Level Rise Effects on Shoreline Position

Abstract

Using a conservation of sand approach, the effects of a rising sea surface are quantified and separated from other causes of shore retreat. Sitespecific data important in predicting shoreline changes are: (1) Initial shoreface and backbeach profile; (2) subsequent backbeach profile; (3) relative sea level rise; (4) grain size distribution of sediment landward of the shoreface; and (5) net quantity of sand‐sized material that enters or leaves a specified coastal reach. A key element of the approach, Bruun's assumption of a shoreface is dynamic equilibrium with the sea surface, was evaluated and found to be reasonably accurate. Field application of the method shows that sea level rise accounts for about 53% of the total shore retreat of 5.5 m/yr measured at Smith Island, Virginia, and for about 88% of the measured, 1.7‐m/yr retreat of the barrier island south of Oregon Inlet, North Carolina. Net sand losses account for the remainder. Because shoreface adjustments are required to maintain an equilibrium profile, sand replenishment is probably the most realistic method to stabilize a shore against the effects of relative sea level rise. Conversely, a negative sediment budget may also be mitigated by structures which hinder the movement of sand away from a problem beach and enhance its deposition there.