Rip Current Generation, Flow Characteristics and Implications for Beach Safety in South Florida

Authors

Stephen B. Leatherman, Florida International UniversityFollow

Document Type

Dissertation

Degree

Doctor of Philosophy (PhD)

Major/Program

Geosciences

First Advisor's Name

Keqi Zhang

First Advisor's Committee Title

Co-Major Professor

Second Advisor's Name

Dean Whitman

Second Advisor's Committee Title

Co-Major Professor

Third Advisor's Name

Michael Sukop

Third Advisor's Committee Title

Committee Member

Fourth Advisor's Name

Shu-Ching Chen

Fourth Advisor's Committee Title

Committee Member

Keywords

Rip current, Beach, Coastal Hazards, Nearshore Currents, Beach Safety, Beach Drowning, South Florida

Date of Defense

11-9-2018

Abstract

Rip currents are the most dangerous hazard at surf beaches. Rip currents in South Florida have previously not been studied. Beach profiles for three Florida beaches (Miami Beach, Lido Beach, Sarasota, and Pensacola Beach) and one Georgia beach (South Cumberland Island) were chosen for surveying because of their variable sand bar heights. Rip current hazard at each beach was assessed by lifeguard rip rescue and drowning statistics. A relationship was found between sand bar height, beach slope and rip current hazard.

Rip current measurements in South Florida, which involved utilizing GPS drifters, laser rangefinder and drone-imaged fluorescent tracer dye, showed that the speed ranged from 0.1-0.5 m/s, which is fairly slow compared to such measurements undertaken in California and Australia. The effect of rip currents on swimmers was analyzed based on the drag force acting on swimmers and the power they generate to overcome the currents when swimming against them. The drag force and power increase quadratically and cubically, respectively, with the increase of rip current and swimming speeds. Hence, even rip currents of low velocity can be dangerous and swimming against the current should be avoided if possible.

Strong rips in California have been shown to exhibit a circulatory pattern, which could bring a floater back to the safety of a shallow sand bar. Field measurements of rip currents in South Florida clearly defined the flow characteristics of a nearly straight-line current, sometimes deflected to the east-southeast. Therefore, the traditional approach of swimming left or right, parallel to the shore is the best escape strategy, but not against the longshore current if present. A logistic regression analysis was conducted to predict the occurrence of rip currents based on beach conditions. The logistic model showed that wave height, wave period and wind speed were statistically significant factors in rip generation. Rips were found to be most commonly generated by relatively small, non-threatening waves (e.g., 0.6 to 0.9m in height). These physical factors, along with social and safety considerations, pose a significant problem for coastal management.

Identifier

FIDC007023

ORCID

https://orcid.org/0000-0002-6889-9177

Recommended Citation

Leatherman, Stephen B., "Rip Current Generation, Flow Characteristics and Implications for Beach Safety in South Florida" (2018). FIU Electronic Theses and Dissertations. 3884.
https://digitalcommons.fiu.edu/etd/3884