GIS and 3D Analysis Applied to Sea Turtle Mortalities and Navigation Channel Dredging

Between 2000 and 2003 there were an increased number of documented sea turtle mortalities related to hopper dredging in the channels of the Chesapeake Bay. A pilot study was undertaken to create a bathymetric surface and three-dimensional model of the Cape Henry Channel using Geographic Information Systems (GIS) as a visualization tool to examine sea turtle mortalities in relation to the dredging. In Fall 2003, the US Army Corps of Engineers dredged the Thimble Shoals Federal Navigation Channel, and a more refined model was developed using this data. This project examines the growing concerns over sea turtle mortality rates and dredging operations, as well as a description of the usage of GIS analysis, interpolation, and visualization methods as tools for examining turtle habitat and mortality issues. Future directions for incorporating G IS into attempts to reduce sea turtle mortality in dredging operations are then outlined. INTRODUCTION AND BACKGROUND The section of the Chesapeake Bay off the Virginia coast contains a series of Federal Navigation Channels that are periodically dredged by self-propelled hopper dredges. These dredges are suitable for all but hard materials and are, by far , the best suited dredges for offshore work (Herbich 2000). There are four main navigation channels in the lower Chesapeake Bay: York Spit, York River Entrance, Cape Henry Channel, and Thimble Shoals Channel. Cape Henry Channel and Thimble Shoals Channel mark the entrance to the Bay from the Atlantic Ocean. The Thimble Shoals and Cape Henry channels are congressionally authorized Federal projects located in the mouth of the Chesapeake Bay between Hampton Roads and the Atlantic Ocean. Thimble Shoals Channel is approximately 18288 meters long, 304.8 meters wide, with an original depth of 13.7 meters at mean low water (CENAO 1973) . The channel was constructed in 1914 and requires maintenance dredging once every 2-3 years. Cape Henry Channel is approximately 328 meters wide and 3.7 kilometers long, with an original depth of 12.8 meters at mean low water (CENAO 1980). Figure 1 shows the locations of the Thimble Shoals channel and a portion of the Cape Henry channel as they relate to the Chesapeake Bay coastline region. 1 Corresponding author, Department of Geography, 1 University Plaza, Youngstown State University, Youngstown, OH 44555. Phone: 330-941-3317. Fax: 330-941-1802. b.ashellito@ysu.edu 2 Phone: 757-201-7418 , keith.b.lockwood@usace.army.mil