tons) and averages 4.3 million metric tons (4.7 million short tons). About 

 30% (1.3 million metric tons, 1.4 million short tons) of this passes through 

 the estuary system to the Gulf of Mexico (Ryan 1969). 



Longshore drift brings a volume of sediment, especially sand, into the 

 Alabama coastal zone. The south and southeast winds cause westward-flowing 

 currents, bringing sediment from the Florida coast into Alabama. The Mobile 

 Bay discharge is a major drift barrier, and much of the westward-moving 

 sediment is carried offshore. Net longshore drift has been measured at 

 Perdido Pass (Pensacola quadrangle) to be 49,699 m 3 (65,000 yd 3 ). Net 

 longshore drift at Gulf Shores (Pensacola quadrangle) has been calculated to 

 be 149,853 m 3 (196,000 yd 3 ) by D. S. Gorsline, using wave-energy calculations 

 (U.S. Army Corps of Engineers 1973a). 



These examples give only brief glimpses of a complex sediment budget. 



Obviously, much work needs to be done on the variations in movement and 



the fate of sediments within the coastal system of Alabama (Hardin et 

 al. 1976). 



Hardin et al . (1976) examined the question of sea-level changes and how 

 this process affects shoreline erosion and accretion, noting that while the 

 National Ocean Survey established 16 control tide stations along the gulf 

 coast to determine the changes taking place in the relative elevations of 

 land and sea, none of these stations is located in Alabama. Based on data 

 gathered over the past 50 years alonq the Florida gulf coast, a subsidence 

 rate of 0.1 mm (0.04 inch) per year was assigned to the lands of the gulf 

 coast from the Mississippi River to Key West, Florida (Lazarus 1965). Bird 

 (1969) cites recent tidal gauge records that indicated continuing changes in 

 the relative position of the land and sea. In areas such as coastal Alabama 

 which has so much low-lying land, this factor of sea level takes on major 

 significance in regard to shoreline configuration. 



Measuring the shoreline of Alabama has proven to be a formidable task. 

 Using conventional opisometry (manually measuring distances on maps using a 

 calibrated wheel), four agencies have arrived at different figures. 



The U.S. Army Corps of Engineers reported the estuary shoreline length at 

 491.2 km (305.3 mi) in Appendix E of the National Shoreline study. The Ala- 

 bama Department of Conservation listed the correct length as 577.5 km (358.9 

 mi). The National Oceanic and Atmospheric Administration stated the length 

 of tidal shoreline in Alabama is 976 km (607 mi). Using an opisometer on 

 large scale maps, the Geological Survey of Alabama obtained a figure of 811.3 

 km (504.2 mi). 



"These measurements are based on traditional map analysis techniques and 

 the difference between them manifests the difficulty encountered in such 

 measurements, including the definition of the parameter being measured" 

 (Hardin et al . 1976). 



The newest sources of shoreline data are the NASA satellites Landsat 1 

 and 2. Satellite data from 28 December 1972 and 5 December 1973 were com- 

 pared and analyzed. While only part of the shoreline of Alabama was measured 



93 



