Impacts of Hurricanes Frances and Jeanne on Two Nourished Beaches along the Southeast Florida Coast

摘要

Site inspections and beach profile surveys of nourished beaches in the city of Boca Raton, and Town of Palm Beach, Florida show that the nourished beaches protected the shore from hurricane impacts in 2004. Striking 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 extending 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 Hurricane 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-induced waves affected the coast at least three days prior to landfall. Field in- spection of the study sites after the passage of both hurricanes 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 accompanied by the formation of well-developed storm bars seaward of pre-storm bars. Beach morphological 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 magnitude and trends of beach performance are hypothesized in an effort to explain the observed beach behavior.