Influence of Inlet / Shoal Complex on Adjacent Shorelines via Inlet Sink Method

Abstract

The region of influence of the inlet on the adjacent shoreline was determined via examination of the inlet's net sink effect. The net sink effect, or volumetric impact, was computed by adding the volume (or rate) of net sand accumulation within the inlet's channels and shoals with the cumulative volumetric losses on adjacent shorelines to conserve sediment mass after accounting for the volumes either added to adjacent beaches or removed from the ebb shoal by means of nourishment and sediment mining. Volume change of the beaches and ebb shoal complex was computed within a geospatial framework consisting of Regional Mapping and Analysis Program (RMAP), ArcGIS and the Surface-water Modeling System (SMS). Inlet-adjacent cumulative volume changes were then examined to discern the minimum distance away from the inlet along which this volumetric impact was manifest. The alongshore influence of the inlet as determined by the inlet sink method for the 1999-2010 time period was found to be 7.4 miles to the north and 5.5 miles to the south. The inlet sink effect for St. Augustine Inlet is 278,000 cu yd/year, balanced by 99,000 cu yd/yr of erosion from the north beaches and 179,000 cu yd/yr of erosion from the south beaches. If managed properly, the inlet could serve as a valuable, long-term resource for the beaches of St. Johns County within the bounds of its sink effect.

Morphodynamics of barrier-inlet systems in the context of regional sediment management, with case studies from West-Central Florida, USA

“…An analytical model may use estimated rates of net longshore sediment transport, regional beach erosion rates, and growth rates of ebb/flood-tidal deltas about an equilibrium value to evaluate a long-term exchange between beaches and inlets (Rosati and Kraus, 2009). Beck and Legault (2012) and Legault et al (2012) offer a technical approach at a project scale, which evaluated an optimal volume of mined inlet shoal sediment that could be used to supply adjacent beach nourishment projects without adversely affecting (a) long-term shoal evolution, (b) wave field on adjacent beaches, and (c) inlet navigability. A similar study by Walton and Dean (2011), evaluated maintenancedredging scheduling of the same inlet through an analytical solution of the Pelnard-Considere equation applied to measured shoreline change rates.…”

Review of coastal tidal inlet morphodynamics in the context of barrier-inlet sustainability

“…Caution is suggested with regards to newly stabilized inlets with jetties and adjacent fillet development, which will trap a considerable quantity of sediment that would otherwise contribute to ebb-tidal delta development. At different stages of development, volumes contained in fillets or attachment locations may be considered closely connected reservoirs in a tidal inlet shoal accumulation (Kraus 2000;Legault et al 2012), and a critical component to any volume change analysis must consider this geomorphological interpretation. Powell et al (2006) provide a comprehensive review of empirical morphodynamic relationships of tidal inlet cross-section area and ebband flood-tidal delta volume to tidal prism using 67 sandy barrier island inlets from Florida for reference.…”

The Effect of Regional Winds on Subtidal Along‐Inlet Currents at Oregon Inlet, NC

“…Because inlets regulate the flux of water, sediment, and nutrients between the ocean and an inland water body, they often play an important role in the ecologic health of the inland system (Fulton et al., 1993) and may exhibit morphologic control well beyond their immediate geographic footprint (FitzGerald, 1988; Hayes, 1980). For example, cross‐shore oriented tidal currents disrupt alongshore sediment transport, temporarily or permanently storing large volumes of sediment in flood and ebb tidal deltas (Boothroyd, 1985; FitzGerald, 1982; Legault et al., 2012; Walton & Dean, 2011). These disruptions may manifest as large scale erosional or accretional patterns over extended swaths of neighboring coastline (FitzGerald, 1988).…”