INFLUENCE OF INLET / SHOAL COMPLEX ON ADJACENT SHORELINES VIA INLET SINK METHOD

Kelly Rankin Legault, Tanya Beck, Jason Engle

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.

Keywords


inlet processes; sediment budget; inlet shoaling; beach volume change

References


Legault K.R., J.D. Rosati, J. Engle, and T.M. Beck. 2012. St. Johns County, St. Augustine Inlet, FL Report 1: Historical Analysis and Sediment Budget. Technical Report ERDC-TR-12-4: Report 1, U.S. Army Research and Development Center, Coastal and Hydraulics Laboratory, Vicksburg, MS.

Taylor Engineering, Inc. 1996. Inlet Baseline Conditions Physical and Environmental Characteristics. St. Augustine Inlet Management Plan – Part 2, St. Johns County, Florida.

Taylor Engineering, Inc. 2003. 2003 Monitoring Report. St. Johns County Shore Protection Project, St. Johns County, Florida.

Taylor Engineering, Inc. 2005. 2004 Monitoring Report. St. Johns County Shore Protection Project, St. Johns County, Florida.

USACE. 2008. Coastal Engineering Manual. EM 1110-2-1100 (Part V) 31 Jul 03. http://chl.erdc.usace.army.mil/cem.

USACE-SAJ. 2010. Dredging Information System (DIS) Database, maintained by the U.S. Army Corps Engineer Jacksonville District, Jacksonville, Florida.


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