Ad J. H. M. Reniers

An Introduction to Rip Currents Based on Field Observations

Abstract Rip currents are fascinating, natural, surf zone phenomena that occur daily on many beaches throughout the world. My colleagues, students, advisors, and I have been studying rip currents for more than 10 years and have performed more than 10 comprehensive field experiments on various beaches throughout the world using different observational techniques and model simulations to improve our understanding and prediction of rip currents. We have written a series of scientific articles describing the intricacies and complexities of rip current behavior using statistical and mathematical equations. These manuscripts are typically published in professional journals, which often do not communicate our results to those who would benefit from the information—the beachgoing public and ocean swimmers. Herein, we summarize our findings to help people of all ages gain a better understanding of currents at the coast.

Assessing the effectiveness of rip current swimmer escape strategies, Shelly Beach, NSW, Australia

ABSTRACT McCarroll, R.J., Brander, R.W., MacMahan, J.H., Turner, I.L., Reniers, A.J.H.M., Brown, J.A. and Bradstreet, A., 2013. Assessing the effectiveness of rip current swimmer escape strategies, Shelly Beach, NSW, Australia . Rip flow dynamics have important implications for swimmer escape strategies, with recent field studies indicating flow is often contained within the surf zone, re-circulating onto shallow bars. Combining physical measurements in a variety of conditions with various escape strategies allows insights into the safest response by individuals caught in a rip. A three day experiment was conducted at Shelly Beach, NSW in December, 2011. Lagrangian measurements of rip flow using GPS drifters were obtained. Participants with attached GPS were deployed in groups of 3 to 5 in rip currents to simulate various escape actions such as floating with the rip current, and swimming in a parallel direction at varying distances from shore. Day 1 and 2 measurements captured an open beach rip current and an adjacent topographic rip current in moderate energy conditions. Day 3 measurements were obtained on an open beach rip current at a more exposed section of the beach under higher energy conditions. Results were analysed by duration and assessed as being either (i) positive outcome (high chance of safe exit); or (ii) negative outcome (greater potential for hazard). Mean durations were Float (4 min), and Swim (2 min). Of the eight escape scenarios tested, half had potential negative outcomes, including 2 of 3 Float options and 2 of 5 Swim options. Negative outcomes for Floats were related to surf zone exits, and multiple circulations. Negative outcomes for Swims related to swimming against longshore directed circulation. Neither strategy was clearly more likely to result in a successful outcome across all scenarios. Further investigations are currently being conducted in a greater range of hydrodynamic and morphological conditions.

Surfzone Monitoring Using Rotary Wing Unmanned Aerial Vehicles

This study investigates the potential of rotary wing unmanned aerial vehicles (UAVs) to monitor the surfzone. This paper shows that these UAVs are extremely flexible surveying platforms that can gather nearcontinuous moderate spatial resolution and high temporal resolution imagery from a fixed position high above a study site. The rotary wing UAVs used in this study can fly for ;12 min with a mean loiter radius of 1–3.5m and a mean loiter error of 0.75–4.5 m. These numbers depend on the environmental conditions, flying style, battery type, and vehicle type. The images obtained from the UAVs, and in combination with surveyed ground control points (GCPs), can be georectified to a pixel resolution between 0.01 and 1m, and a reprojection error—that is, the difference between the surveyed GPS location of a GCP and the location of the GCP obtained from the georectified image—of O(1 m). The flexibility of rotary wing UAVs provides moderate spatial resolution and high temporal resolution imagery, which are highly suitable to quickly obtain surfzone and beach characteristics in response to storms or for day-to-day beach safety information, as well as scientific pursuits of surfzone kinematics on different spatial and temporal scales, and dispersion and advection estimates of pollutants.

Morphological developments after a beach and shoreface nourishment at Vlugtenburg beach

Typically a beach is out of equilibrium after a nourishment is installed. To observe how a nourished beach behaves on the timescale of storms a monitoring campaign was set up at Vlugtenburg beach after a nourishment in the spring of 2009. Here we show a sediment budget analysis of the first 2.5 years for a coastal domain spanning 1750 m alongshore from -9 to +5 m NAP. To investigate the redistribution of nourished sand different sections of the profile are examined. Observations show that the initial response (first 6 to 12 months after construction) is large where the sediment eroded from the beach is transported offshore to form a subtidal bar. In the following period (until present) the losses in the domain are on the order of 40 m3 per m alongshore per year. These losses are concentrated in the profile around the waterline.

Research Overview of the Consortium for Advanced Research on Transport of Hydrocarbon in the Environment (CARTHE)

ABSTRACT CARTHE (http://carthe.org/) is a Gulf of Mexico Research Initiative (GoMRI) consortium established through a competitive peer-reviewed selection process. CARTHE comprises 26 principal inve...