The effects of Hurricane Ivan on Perdido Key, Escambia County Florida.
ABSTRACT Hurricanes are extremely destructive forces of nature. Barrier islands often take the hardest hit when hurricanes make landfall because they are low lying land located right on the coast. On September 16th, 2004, Hurricane Ivan made landfall near Gulf Shores, Alabama as a category 3 hurricane, causing extensive damage to the barrier islands and coastal areas of Alabama and western Florida. Some of the most intense damage from Ivan occurred in the Pensacola, Florida area. The objective of this research was to document Ivan's impact on the geomorphology and human structures of Perdido Key, a barrier island off the coast of Pensacola, Florida. The National Oceanic and Atmospheric Agency (NOAA) took post Hurricane Ivan air photos that were georeferenced for this study using before hurricane air photos gathered from the Florida geographic library database. Analysis and comparison of pre and post Ivan photos shows numerous impacts, including overwash fans, burial of large areas under sand, and damage to or failure of numerous man-made structures. Keywords: Hurricane Ivan, GIS, coastal modification, Florida, 2004 hurricanes, barrier islands
Hurricanes are some of nature's most impressive storms. Areas in the United States at high risk for hurricane landfalls include the states of the Gulf of Mexico and Atlantic coasts from Texas up through the Carolinas (1). This region contains over 73 million people, or approximately 25% of the population of the United States (2). Hurricanes can cause significant geomorphic change to coastal areas (3), with the greatest geological effects coming from wind generated waves and storm surges (4). Storm surge damage is often most intense in the northeast quadrant of the storm (1). During a storm surge, sand may be deposited as overwash fans and extensions of beaches, while erosional features include barrier islands being cut through and loss of beach front (5). Storm surges can also cause significant property damage (1), and vegetation and buildings may be damaged by wind because as wind blows around an object it generates an area of low pressure, creating suction on the opposite side (6). When winds break a window it can cause building failure by blowing off the weakly attached roof (6).
Worldwide, damage caused by hurricanes can cost many billions of dollars in destruction of roads, homes, business, and other lost property, and lives are also lost to these storms (7). Barrier islands are at particular risk of damage from hurricanes because they are the first land encountered by a storm coming ashore and they tend to have elevations below 5 m (7). Hurricanes hitting barrier islands have caused large losses of both property and lives in the United States, with some of the more notable examples including Galveston TX in 1900 and the Great Miami Hurricane of 1926 (8). Improved hurricane forecasting has saved many lives in recent years, but as more and more people move to coastal areas the potential for catastrophe increases (1).
Hurricane Ivan made landfall as a Category 3 hurricane with maximum sustained wind speeds of 195 km [h.sup.-1] (120 mph) on September 16, 2004 at 1:50 am (Central Time) near Gulf Shores, AL (Figure 1) (9). The area around Pensacola, FL, located about 50 km (30 miles) east of Gulf Shores, was heavily hit and suffered significant damage from Ivan. Official records from the Pensacola Naval Air Station (PNAS) showed sustained wind speeds of 140 km [h.sup.-1] (87 mph) with gusts up to 172 km [h.sup.-1] (107 mph) (9). The storm surge at the PNAS reached into the second story of many of the buildings (10). Documented changes on Santa Rosa Island, a barrier island located southeast of Pensacola, included a new breach of the island, several overwashed areas, and building and home destruction (11).
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This study was undertaken to investigate the effect a strong hurricane can have on the barrier island environment, looking at impacts on both geomorphic and anthropogenic systems. The study area is Perdido Key (Figure 2), the western most barrier island off the coast of Florida and the closest barrier island in Florida to the place where Ivan came ashore. Perdido Key was in the northeast quadrant of the storm. National Hurricane Center records indicate that the narrow band of strongest winds at landfall likely occurred at Perdido Key, and the storm surge in Escambia County (which includes Perdido Key) was reported as 3 to 4.6 m (10 to 15 ft) (9). Given the high storm surge and strong winds, Perdido Key seemed to be an ideal place to study the impact of a major hurricane on an inhabited barrier island.
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MATERIALS AND METHODS
This project was based on comparisons of before and after Ivan aerial photographs. The before Ivan aerial photographs were published in 2001 and collected from the Florida Geography Library Database (www.fgdl.org). The after Ivan aerial photographs were taken by the National Oceanic and Atmospheric Agency (NOAA) shortly after Ivan made landfall and were obtained at http://www.ngs.noaa.gov/ivan/IVAN00.HTM. The Ivan images were taken off the NOAA website in 2005 to make room for aerial photographs of areas affected by the 2005 hurricanes.
The NOAA pictures were not georeferenced; therefore, one of the first steps in this project was to georeference them. The NOAA photographs were placed on top of the before Ivan aerial photos in ArcGIS 9.0 (Environmental Systems Research Institute Inc., Redlands, CA). Control points such as buildings, road intersections, and docks were used to line up the before photos with the after photos. Projections also had to be established for the NOAA after pictures because they were merely JPEG files and carried no projection data with them. The before pictures from the Florida Geographic Library Database had projection data which allowed complete georeferencing of the NOAA photos. Following the georeferencing of the after photos, before and after photos were paired up and compared for changes caused by Hurricane Ivan.
A number of changes were seen on Perdido Key when comparing the before and after pictures. The coastline was straightened in places (Figure 3) and massive overwash fans were present at a number of locations (Figure 4). Large scale movement of sand was apparent across the entire study area (Figure 5). Man-made structures were severely damaged during hurricane Ivan; property damage can be seen in almost all the photographs. Wide-spread burial of features such as parking lots, roads, and tennis courts took place (Figures 4 and 5). Some buildings were flattened by wind and/or storm surges while other buildings were badly damaged, including missing roofs and/or missing sections of the building (Figure 6). Several boathouses and their associated piers were also damaged (Figure 7).
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The use of aerial photography has advantages and disadvantages. Aerial photos permanently record how a given area looked at a given point in time, and can provide more detail than maps. Because of their dynamic nature, coastlines are photographed more that they are mapped (12). However, pictures can only show horizontal changes to the topography, they can not show volume. While it is possible to document damage to buildings, movement of sand on Perdido Key, and make estimates of the area covered by newly moved sand using GIS and aerial photography, it is not possible to calculate the volume of sand that was moved over any given area.
Several geological effects have been documented during hurricanes. Among the most common is the movement of sand, both erosion and deposition, by overwash and wind (4), (6). The aerial photographs provide ample evidence of these processes taking place on Perdido Key during Hurricane Ivan. Overwash fans were observed and large areas of roads, parking lots, and other such features were covered by sand in the post-Ivan photographs. Ivan also caused extensive damage to a number of buildings on Perdido Key. Roofs were damaged, walls were knocked down, and in some cases, entire buildings disappeared, with only the foundations remaining. A number of piers and boathouses also sustained damage during Ivan. Again, these effects are consistent with what has been seen in the past after a major hurricane (6). The recent movement of people to the U.S. coast exasperates this problem (13), as more property is placed in the potential path of hurricanes leading to increasing economic losses when a major hurricane strikes (Table 1). Ivan showed that despite advanced weather forecasting and improvements in our ability to predict the path and strength of hurricanes, major storms are still a significant threat to populated coastlines.
Barrier islands are directly in the line of fire whenever a hurricane comes ashore. Hurricanes have the ability to change the shorelines and the body of barrier islands drastically, causing loss of lives and property in a short amount of time. Many changes happened to Perdido Key. Thousands of square meters of sand was displaced. Roads were covered and buildings were destroyed. Evidence of the hurricane can be seen across the island and into the lagoon behind it in the form of damaged piers and boathouses. Yet, despite this, humans are drawn to coastal areas. Over 60% of the world's population lives in coastal areas, and more people move the US coast every year (13). For this reason, it is becoming more important than ever that we understand storms like Hurricane Ivan and the damage they are capable of inflicting, and that we manage this national move to the coasts in a way consistent with that knowledge.
Table I. Estimates of damage caused by the costliest hurricanes to hit the United States mainland, standardized to 2004 dollars. Hurricane Year Damage Estimate * Katrina 2005 100-150 billion Andrew 1992 26.5 billion Charlie 2004 15.0 billion Ivan 2004 14.2 billion Frances 2004 8.9 billion * - Katrina estimate from (14), other estimates from (15).
ACKNOWLEDGEMENT AND DISCLAIMER
The research reported in this paper was conducted when K. Pate was an undergraduate student in the Department of Physics, Astronomy, and Geosciences at Valdosta State University. Trade names or commercial products are given solely for the purpose of providing information on the exact equipment used in this study, and do not imply recommendation or endorsement by Valdosta State University.
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(10.) Charles Brevik, verbal communication, November 10, 2004.
(11.) USGS: http://coastal.er.usgs.gov/hurricanes/ivan/index.html, 2004. Accessed 10/20/2004.
(12.) Anders FJ and Byrnes MR: Accuracy of shoreline change rates as determined from maps and aerial photographs. Shore and Beach 59(1): 17-26, 1991.
(13.) Marshak S: "Earth: Portrait of a Planet." New York: WW Norton&Co., Inc., 2005.
(14.) http://sciencepolicy.colorado.edu/prometheus/archives/disasters/000563part_ii_historical.html, 2005. Accessed 2/24/2006
(15.) http://www.nhc.noaa.gov/pastcost.shtmlhttp://www.nhc.noaa.gov/pastcost.shtml, 2004. Accessed 2/24/2006.
Katrina M. Pate, Eric C. Brevik *, and Paul C. Vincent
Department of Physics, Astronomy, and Geosciences
Valdosta State University
Valdosta, GA, 31698-0055
email@example.com, firstname.lastname@example.org, and email@example.com.
* - corresponding author
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|Author:||Pate, Katrina M.; Brevik, Eric C.; Vincent, Paul C.|
|Publication:||Georgia Journal of Science|
|Date:||Jun 22, 2006|
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