T247 Sigma Gamma Epsilon Undergraduate Research (Posters)

Tuesday, 29 October 2013
9:00 AM - 6:30 PM
Hall D

AN ASSESSSMENT OF SHORELINE CHANGE FOR SMALL ASSOCIATED ISLANDS OF PUERTO RICO AND THE UNITED STATES VIRGIN ISLANDS

Paper number: T247-84
Program: Technical Sessions
Time: 9:00 AM – 6:30 PM

Authors

Abstract

Perhaps no information is more critical for coastal management than shoreline change history. In this study we evaluated historical shoreline change of twenty associated islands of Puerto Rico and the United States Virgin Islands. Historical shoreline position data was digitized from NOAA t-sheets and aerial photographs. The historical shorelines were digitized as continuous lines. The Shoreline position rate of change was calculated using end point rate in the AMBUR program (Jackson et al., 2012). Transects were derived every 10 meters, resulting in a total of 5,234 transects among all the study area islands. The length of all shorelines digitized totaled 106 km. The total area of all the islands in the study was 609.97 hectares (just over 1,500 acres).

Maximum erosion measured for a single transect was 132.35 meters, the maximum accretion for a single transect was 69.42 meters. The overall mean change was -4.7 meters, and the overall mean rate of change was -0.12 m/yr. Within individual islands, the greatest shoreline change rate is -0.83 meters/year, exhibited by Cayo Ratones. Many of the islands are very nearly stable. Cayo Ratón. Cayo Santiago, Isla Magueyes, and Isla de Cardona exhibit accretion. While erosion is dominant on the island shorelines, it is not a rapid rate of change. And in fact, the mean shoreline change rate on all but five of the islands is within the statistical margin of error of +/- 0.2 m/yr. The largest percentage of an island’s shoreline exhibiting erosion is 95%, found on Cayo Ratones, Isla de los Palomas, and Isla Morrillito. Measurements reveal a total area of land loss for all 20 islands of 20.32 hectares (50.2 acres).