St. Johns County, St. Augustine Inlet, FL, Report 1: Historical Analysis and Sediment Budget
Abstract
This report is the first in a series documenting analyses for St. Augustine Inlet and adjacent beaches within St. Johns County, Florida. The study quantified beach and inlet volumetric change to evaluate the historical and future impacts of the ebb shoal mining and adjacent beach nourishment. The majority of the analyses applied volume change from 1999 to 2010 determined from adjacent beach profiles and bathymetric surveys of the inlet. The total rate at which the inlet removed sand from the littoral system, the "total inlet sink," was balanced by volume change north and south of the inlet. A system of equations was developed to use these measurements and ranges in viable net and gross transport rates to develop a "Family of Solutions" representing viable sediment budgets for the region. The centroid of a narrowed set of solutions was formulated into a representative 1999 to 2010 sediment budget. Findings indicated that the alongshore extent of inlet impact south of the inlet for the 1999 to 2010 period were similar to a previous budget from 1974 to 1995, but extended further north during the later period. The rate at which the inlet removed sand from the littoral system was less in the latter 1999 to 2010 period relative to the former 1974 to 1995 period, indicating the ebb shoal continues to decrease the rate of accretion. Through examination of the time rate of change for the ebb shoal from 1940 to 2010, the accretion rate has decreased by 320,000 cu yd/yr over the 70 years examined. The study also evaluated whether the behavior of the beach and/or inlet changed fundamentally following either 2003 or 2005 mining of the ebb shoal. All of the analyses indicated that the inlet trapped less sediment in the postdredge time period than it had before dredging. While the processes governing why the inlet might have trapped less is still an active topic of speculation, it is evident that the inlet borrow area did not cause an overall increase in sediment trapping.
Document Details
- Document Type
- Technical Report
- Publication Date
- Aug 01, 2012
- Accession Number
- ADA570209
Entities
People
- Jason Engle
- Julie Dean Rosati
- Kelly Legault
- Tanya M. Beck
Organizations
- Engineer Research and Development Center