Vol. 9, No. 12 December 1999 INSIDE Section Meetings • Northeastern, p. 14 GSA TODAY • Southeastern, p. 18 A Publication of the Geological Society of America • South-Central, p. 22 Hurricanes Dennis and Floyd: Coastal Effects and Policy Implications Robert S. Young, Department of Geosciences and Natural Resources Management, Western Carolina University, Culhowee, NC 28723, [email protected] David M. Bush, Department of Geology, State University of West Georgia, Carrollton, GA 30118, [email protected] Andrew S. Coburn, acoburn@alumni. duke.edu, Orrin H. Pilkey, opilkey@geo. duke.edu, Program for the Study of Developed Shorelines, Division of Earth and Ocean Sciences, Nicholas School of the Environment, Duke University, Durham, NC 27708 William J. Cleary, Center for Marine Science Research, UNC—Wilmington, 601 South College Road, Wilmington, NC 28403-3297, [email protected] ABSTRACT Tropical systems Dennis and Floyd impacted eastern North Carolina in Figure 1. Erosion on Oak Island, North Carolina by Hurricane Floyd in 1999. Pilings on the house and 1999, the fourth and fifth storms in exposed, broken septic tanks lining the beach indicate that the beach profile was lowered approximately three years to make landfall in this area. 1 m during the storm. Septic tanks are emplaced with drain fields above the water table, which limits All five storms were very similar in their location in nearshore environments. As an example of the range of impacts of human development in the coastal zone, before Floyd the recreational beach was situated directly above these septic systems. strength (wind speed); however, the effects on the coast were quite different. In addition to absolute storm strength, morphological changes to the natural INTRODUCTION meteorologists and the popular media environment were controlled by the for- described the first of these (Bertha) as a The probability that a hurricane will ward speed of the storms, orientation of 50-year storm—a storm that would be make landfall at any given point along the the shoreline relative to storm track, expected to recur once every 50 years. All coast in any one year is low, and the even underlying geology, impacts of recent five storms in this three-year period were lower probability of a great hurricane storms, and associated rainfall. Damage of comparable strength and had varying (category 3, 4, or 5) makes such an event to buildings was a function of the place- coastal impact. Obviously, our concept of seem extremely unlikely. But low probabil- ment of structures with respect to the a 50-year storm may need some adjust- ities give a false sense of security, because shoreline and the removal of weaker ment. It is also clear that despite recent the lesson of hurricane history tells us that buildings by previous storms. On the improvements in hurricane forecast mod- in the lifetime of a building such a storm basis of these observations, we recom- els, long-term forecasting is still difficult if is almost a certainty. Furthermore, the mend a new Hurricane Impact Scale, not impossible, as demonstrated by both occurrence of a hurricane one year does which will allow prediction of possible 1999 storms. We describe here the geologi- not reduce the likelihood that a similar storm impacts and comparisons of cal impact of these two storms in North storm will strike again the next year. coastal impacts in other hurricanes. Carolina, and we discuss our views on the The coast of North Carolina was Each additional hurricane demon- coastal zone management lessons to be struck by two hurricanes in 1996 (Bertha strates that our society does not have a learned and the need for a new scale to and Fran). It happened again in 1999. forward-looking plan for dealing with communicate predicted and observed Hurricane Dennis impacted the coast for coastal storms. Instead, we typically coastal storm impacts. several days, from August 30 to September repair and rebuild in place, and con- 4. Hurricane Floyd made landfall on tinue the upward spiral of property HURRICANE DENNIS September 16, causing record flooding damage in storms. Although the dollar across most of eastern North Carolina and Dennis tracked up the U.S. East Coast amount of property damage will be low damage to shoreline structures in some as a category 3 hurricane on the Saffir- from these storms, the public must bear places (Fig 1). These were the fourth and Simpson scale of hurricane intensity, the cost of cleanup and repair of infras- fifth storms to strike the North Carolina stalling off the Outer Banks of North tructure. coast in the past three years (Fig. 2). Local Hurricanes continued on p. 2 IN THIS ISSUE GSA TODAY December Vol. 9, No. 12 1999 Hurricanes Dennis and Floyd: Toward a Stewardship of the Global Coastal Effects and Policy Commons ............................. 25 GSA TODAY (ISSN 1052-5173) is published monthly by The Geological Society of America, Inc., with offices at 3300 Implications .......................... 1 Penrose Place, Boulder, Colorado. Mailing address: P.O. Box Call for Applications and Nominations 9140, Boulder, CO 80301-9140, U.S.A. Periodicals postage Dialogue .............................. 3 for GSA Bulletin Editor ................. 26 paid at Boulder, Colorado, and at additional mailing offices. 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The tally by storms during times of rising sea diverse opinions and positions by scientists worldwide, storm then reversed course, remaining off level (Leatherman et al., 1982; Nummedal, regardless of their race, citizenship, gender, religion, or polit- ical viewpoint. Opinions presented in this publication do not North Carolina until it made landfall 1983; Leatherman, 1983a, 1983b). Pilkey reflect official positions of the Society. across Core Banks on Saturday, September et al. (1998, p. 44–47) described barrier 4 (Fig. 2). By that time Dennis had weak- island migration with North Carolina SUBSCRIPTIONS for 1999 calendar year: Society Members: GSA Today is provided as part of membership ened to a tropical storm (sustained winds examples as a three-step process. Barrier dues. Contact Membership Services at (800) 472-1988, less than 119 km/h). islands migrate landward by: (1) shoreline (303) 447-2020 or [email protected] for member- Hurricanes usually move ashore retreat on the open ocean side, (2) eleva- ship information. Nonmembers & Institutions: Free with paid subscription to both GSA Bulletin and Geology, quickly, minimizing the time available to tion of the island by the addition of over- otherwise $50 for U.S., Canada, and Mexico; $60 else- erode beaches, but Dennis stayed offshore wash sand, and (3) movement of the where. Contact Subscription Services. Single copies may be requested from Publication Sales. Also available on an for several days, producing large waves island’s soundside shoreline landward by annual CD-ROM, (together with GSA Bulletin, Geology, GSA much like a stalled winter storm or