Erosion Assessment - Tract IX Cloister Residences East Lots

Letter submitted by Dr. Chester W. Jackson Jr., Assistant Professor of Geology, to the Islands Planning Commission. Included are two pdf studies of historic coastlines.

Dear Islands Planning Commission,

I was recently made aware of the proposed development of Tract IX, Cloister Residences East lots and wanted to briefly share with you my concerns from a coastal geological processes standpoint.  I’ve attached two maps that contain historical shorelines and erosion control structures of the Sea Island barrier spit region.  In the first map (Sea Island spit dynamics 2013 a.pdf), one can see the dynamic nature of the spit as it has both elongated and shortened over time the since the 1800s.  The latest delineated shoreline in the map was in 2003, however, the underlying aerial image from 2013 shows the spit has not only shortened, but the oceanfront has eroded approximately 150+ ft. in front of the proposed development.  This is more visible in the second map (Sea Island spit dynamics 2013 b.pdf).  Furthermore, the proposed development is situated downdrift of a shoreline structure (groin) that is reducing/impeding sediment transportation to the area.  Updrift of the groin and north of the proposed development, there is noticeable accretion (shoreline build-out).  A classic attribute of groins are that they trap sediment on one side (updrift of sediment transport) and tend to enhance/promote erosion on the downdrift side.  
 
Based on my earlier work and research I’m currently conducted that is funded by NOAA and Georgia Sea Grant, I do not believe the proposed project is situated in an area suitable for development.  To sum up things up briefly, the lots are situated:
 
  1. In an inlet hazard zone given how dynamic the shoreline/spit has moved in response to changes in Gould’s Inlet.  These dynamics are also observed on Blackbeard Island’s spit and Cabretta Inlet here in Georgia.
  2. On a young active/mobile and low topographic profile (elevation) barrier island feature sensitive to sea level rise and inundation from coastal storms as evidence by historical overwash features found in the area.  Imagery of the Sea Island spit from Hurricane Dora (1964) showed the area was overwash and inundated from a storm with a landfall track that was near St. Augustine, Florida.
  3. Where oceanfront erosion rates appear to be accelerating since the 1930s and the lots are in a chronically eroding area.
  4. Downdrift of a groin structure that appears to be enhancing erosion within the area given the observed shoreline displacement/offsets on both sides of the structure. There is noticeable accretion on the updrift side of the groin.
I am happy to provide more detailed information if necessary.  My concerns are centered on reducing the construction of development in highly vulnerable coastal areas based on some of the latest research we have been conducting.  Hopefully, you will find these points beneficial to your planning process.  Thanks for your time.
 
Sea Island Spit Dynamics - Overview      Sea Island Spit Dynamics - Close-Up
 
cj
________________________________
Chester W. Jackson Jr., Ph.D.
Assistant Professor of Geology
Department of Geology & Geography
Georgia Southern University
P.O. Box 8149
Statesboro, GA  30460-8149
(912) 478-0174
 
 
Applied Coastal Research Laboratory
Georgia Southern University
10 Ocean Science Circle
Savannah, GA  31411
(912) 598-2328

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