Gulf of Mexico Origin, Waters, and Biota: Volume III, Geology

6. Beaches, Barrier Islands, and Inlets of the Florida Gulf Coast

89 ␥ near 50 cm but it is only about 20–30 cm along the rest of the Florida Gulf Coast (Tanner 1960). The wide and gentle gradient of the peninsular shelf of the Florida Platform helps to absorb wave energy, whereas the relatively narrow and steep panhandle coast permits more wave energy to reach the shore. The wide and gently sloping peninsular shelf is a significant factor in potentialhurricaneinfluencealongtheFloridaGulfCoast. Onshore winds and storm surge along the Gulf peninsula have the potential for much higher water levels than on the panhandle, all other factors being equal. The predicted 100-year storm surge along the peninsular coast is 4 m, whereas it is about a meter less along the panhandle. Historically, the panhandle has been subjected to more frequent and more damaging hurricanes than has the peninsular coast (Fig. 6.2). Prior to Hurricane Charley in 2004 there had not been a major hurricane on the peninsular Gulf Coast since Donna (1960) and before that the unnamed hurricane of 1921. The storm of 1848 also had a major impact on the peninsular coast. By contrast the panhandle has been subjected to 4 major hurricanes in the past decade (Opal in 1995, Ivan in 2004, and Dennis and Katrina in 2005) as well as several minor ones. The storms that enter the Gulf of Mexico typically do not turn northeastward and move on to the west peninsular coast of Florida (Fig. 6.2). The nature of the regular weather systems and the waves that they produce result in rather uniform sediment transport along these barrier coasts: from east to west along the panhandle and from north to south along The Gulf Coast of Florida includes 4 geomorphically distinct provinces. From south to north they are: (1) southwest Florida, which includes the tide-dominated Ten Thousand Islands and south to Cape Sable at Florida Bay, (2) the mixed-energy barrier–inlet system of the central coast, (3) the tide-dominated Big Bend coast, and (4) the wave-dominated barrier coast of the panhandle (Fig. 6.1). This diverse coastal morphology has been variously impacted by hurricanes over geologic time and by human activity of a wide range of types and intensities during the past century. The discussion will consider our state of knowledge of how these coastal provinces and their contained elements have been behaving during the period of intense development pressures and rising sea level and also will consider how they will behave during the next several decades. Emphasis will be on the 2 barrier island systems because these are the ones that are impacted most severely by human intervention and that experience the most change. Coastal Conditions This coast is generally one of low physical energy with higher energy in the panhandle coastal region. Tidal range is microtidal throughout with the barrier systems with less than a meter range at mean tide. The other 2 tide-dominated provinces have tidal ranges of just over a meter, and their tide domination is a result of the low wave energy. The mean wave height in the panhandle is 6 Beaches, Barrier Islands, and Inlets of the Florida Gulf Coast Richard A. Davis Northwest Barrier Chain Apalachicola River Delta B i g B e n d M a r s h C o a s t W e s t C e n t r a l B a r r i e r C h a i n Gulf of Mexico E a s t C o a s t B a r r i e r C h a i n 2 0 0 m 2 0 0 m A t la n t ic O c e a n Ten Thousand Islands Cape Romano Mangrove Coast Cape Sable Everglades F l o r i d a 31°30′N 24°N 88°W 79°W Florida Bay Figure 6.1. Map of Florida showing the major coastal elements . Figure 6.2. Map of Florida showing the location of landfall for all hurricanes between 1885 and 1985.Arrows indicate direction of hurricane at landfall. Numbers appearing at the tail of arrows represent the year of hurricane landfall. Beaches, Barrier Islands, and Inlets ~ 91 provide for both recreational activity and protection of upland property. Many of these structures have caused more problems than they have solved (e.g., Doyle et al. 1984). Now seawalls are not permitted and groin construction is much...