A GEOLOGICAL & GEOPHYSICAL SITE SURVEY
OF DEADMAN'S ISLAND AND OLD NAVY COVE
AT GULF BREEZE, FLORIDA

Introduction

Authors: Daniel C. Phelps, P.G. #1203, Michelle M. L. Ladle, James G. Sparr

Deadman’s Island lies near the mouth of Pensacola Bay adjacent to the City of Gulf Breeze in Santa Rosa County, Florida. It has been experiencing shoreline erosion, especially upon its northern end, in recent years. It and the adjacent waters of Old Navy Cove to its west comprise a historically sensitive area. Old Navy Cove consistently appears on all available historical maps of the region. Old Navy Cove apparently provided and still provides a protected anchorage for vessels from the colonial period to the modern era. The Florida Geological Survey’s investigation was designed to establish:

  • the geological underpinnings of Deadman’s Island;
  • the nature and distribution of the sediments lying on the seabed adjacent to Deadman’s Island; and
  • to determine if sediments from dredge spoil areas on the south end of Deadman’s Island and to the northeast of it sufficiently match those on the north end of Deadman’s Island for the purposes of its restoration.

The FGS grab sampled the island’s beach sediments as well as the seabed of Old Navy Cove. Additionally, FGS collected ground penetrating radar data in two transects down its length. The north end of the island is slated to be restored. The FGS also collected vibracores and hammer cores from both the island and the proposed borrow sites. Analysis of these data has produced:

  • a bathymetric chart of Old Navy Cove;
  • side scan sonar mosaics imaging the seabed of Old Navy Cove;
  • a stratigraphic analysis of the sediments immediately underlying Deadman’s Island;
  • a granulometric analysis of the in situ sediments of Deadman’s Island; and
  • a granulometric analysis of those sediments, both on and off Deadman’s Island, which are anticipated to be used to restore its northern end, as well as a comparison of how well they match the sediments in the area to be restored

This report documents the findings of the FGS’s investigations. It discusses in detail those data obtained and presents conclusions drawn from those data. Information derived from this study will assist state and local officials in making decisions concerning the restoration of Deadman’s Island and the protection of the resources of the island and Old Navy Cove immediately adjacent to it.

This report includes photographs and granulometric analyses of samples collected by the FGS on Deadman’s Island and from a proposed borrow site nearby, as well as descriptions of sediments collected offshore of it in Old Navy Cove. Additionally, the ground penetrating radar data collected on the island and side scan sonar data collected in Old Navy Cove are presented as radiograms and side scan sonar mosaics, respectively. This information can be accessed using one of the following methods:

  • Through the “on-disk” ArcGIS Project. The ArcGIS project contains links to web pages and pdf files of vibracores, beach samples, seabed samples and seismic lines residing on the CD.  Instructions are included on the ArcGIS page of the CD.
  • From the appropriate indices within the CD.
  • From the pertinent appendices within this report text.

The links at the top of each page have been provided to help the user explore this DVD. This introduction page explains these links and introduces the information that is provided on the pages at their destinations. This DVD was designed so that all links to pages other than the six main web pages (Intro, ArcMap Project, Beach Samples, Seismic, Sea Bed Samples, Vibracores) open in a separate window. Please use the "x" in the upper right hand corner to close the window.  When opening larger views of images, the image can be expanded by running your curser over the image and clicking on the button that appears in the lower right-hand corner.  If this is repeated, it will be shrink the image to once again fit in the browser.  

This DVD has been tested on machines running  Windows 98, Windows 2000, Windows XP and Internet Explorer.

  • Introduction

    This is the current page you are looking at.

  • Report

    This document explains in detail the scope and purpose of this investigation. Links have been provided throughout the text to help the reader locate information provided on the DVD. The table of contents is linked to sections of the document and also to pages within this DVD. This document is provided as an adobe pdf file; you must have the free adobe reader loaded on your machine to open it.

  • Study Area Map

    This page provides a link to both the ArcMap and ArcPublisher projects as well as information on it's creation and how to use it.

  • Island Sediments Index

    Island Sediment Sample Index page. This index provides links to sample data pages as well as to each sample's grain size analysis.

  • Vibracore Index

    The Vibracore Index page. This index supplies links to individual data pages for vibracores collected in 2008.

  • Hammer Core Index

    Hammer Core Index page. This index supplies links to individual data pages for hammer core pushcores collected in 2008.

  • Bottom Sample Index

    Bottom Sample Index page. This index provides links to each sample's photo and description.

  • Sidescan Data

    Sidescan Sonar Data Index page. This index includes links to both large-scale mosaics as well as individual line examples.  Each of these can be viewed as a pdf file, and you must have the free adobe reader loaded on your machine.