Impacts of Hurricanes Frances and Jeanne on Two Nourished Beaches along the Southeast Florida Coast • By Lindino Benedet,^-^ Thomas Campbell,' Charles W. Finld^,^Marcel J.F. Stive,^ and Rick Spadoni^ 1. Coastal Planning & Engineeiiing, Inc. 2481 N.W. Boca Raton Blvd, Boca Raton, FL lbenedet@coastalplanning.net 2. Delft University of Technology, 2600 GA Delft, The Netherlands ABSTRACT Site inspections and beacli profile surveys of nourislied beaclies in the city of Boca Raton, and Town of Palm Beach, Florida show that the nour- ished beaches protected the shore from hurricane impacts in 2004. Striijing the southeast coast of Florida within 20 days of each other. Hurricane Frances (Sept. 5, 2004) and Hurricane Jeanne (Sept. 25, 2004) had hurricane-force winds extend- ing more than 120 miles from the center. The eye of Frances made landfall as a Category 2 storm and Jeanne made landfall as a Category 3 storm on the Saffir-Simpson HuiTicane Intensity Scale, Above-average waves and surge affected the entire Florida east coast. Although these beaches were on the return or weak side (southwest quadrant with winds from the southwest as the eye traversed the shore) of both hurricanes, hurricane-uiduced waves affected the coast at least three days prior to landfall. Field in- INTRODUCTION P ost-storm beach profile surveys were conducted on two nourished beaches to evaluate the impacts of Hurricane Frances and Hurricane Jeanne. The pur- pose of this paper is to compare these post- storm data with antecedent data sets to assess the performance of these nourished beaches under the high-energy conditions induced by the 2004 hunicanes. The pre- and post-storm beach sm-veys provided elevation data that was used to (1) de- pict cross- and alongshore morphological changes and to (2) quantify hurricane-in- duced volumetric changes of the projects investigated. The nourished beaches investigated in this paper, Boca Raton and the town of Palm Beach (Figure 1), were directly im- pacted by Hurricanes Frances and Jeanne which struck the southeast Florida coast within 20 days of each other on Sept. 5 and Sept. 25, 2004, respectively. The approxi- mate hurricane tracks and affected coastal segments are shown in Figure 1. Both storms had hurricane-force winds (i.e., velocities in excess of 74 miles per hour) extending more than 120 miles from the center. The eye of Frances made landfall spection of the study sites after the passage of both hunicanes showed significant beach erosion and loss of berm elevation. Damage to infrastructure landward of the nourished beaches was minimal while non-nourished beaches located a few miles to the north and south of the renourished beaches sustained some damage. Beach profile surveys indicated that, as a general trend, beach and inner surfzone erosion was ac- companied by the formation of well-developed storm bars seaward of pre-storm bars. Beach mor- phological responses at the town of Palm Beach were a function of offshore geomorphology of the reef system and the presence of high relief rock outcrops located within the surf zone. Sand that eroded from the renourished beach was deposited seaward of rock outcrops in the surf zone but the rock outcrops had no measurable sediment build up. Causes of the magmtude and trends of beach performance are hypothesized in an effort to ex- plain the observed beach behavior. as a Category 2 storm and Jeanne made landfall as a Category 3 storm on the Saf- fir-Simpson Hurricane Intensity Scale. Above-normal waves and surge affected almost the entire Horida east coast. Al- though the study beaches were on the return or weak side of both hunicanes (south- west quadrant with winds backing from the southwest as the eye traversed the shore), above-average waves attacked the studied beaches for a significant period of time. Deepwater significant wave heights of 29 feet and 28 feet during Jeanne and Frances were respectively recorded by a wave buoy offshore Cape Canaveral, located north of the study beaches. Field inspection of the three study sites after the passage of both 0 so 100 200 300 400 ^^^^^^^^^^^^^''^'''''''''''''''t^^m^^^mmm^^^^^^^^^'''''^ Kilometers Figure 1. Location of nourislied beaclies along the southeast coast of Florida. The towns of Palm Beach and Boca Raton are of tlie study areas reported in this paper. The light-colored circle indicates tlie approximate area affected by hurricane-force winds during landfall. Hurricane Frances made landfall on Sept. 5, 2004, while Hurricane Jeanne made landfall at tlie same general location on Sept. 25, 2004. Sliore & Beach Vol. 73, No. 2 & 3, Spring/Summer 2005, pp. 43-48