Abstract

Rip currents are known as one of the most dangerous hazards on sandy beaches worldwide. Indian beaches are least explored to study the variability of rip currents in space and time. The present study is the first attempt made to understand its dynamics by utilizing indigenously developed GNSS (Global Navigation Satellite System) drifters and Rhodamine-B dye experiments. The Rama Krishna (RK) and Rushikonda Beaches of Visakhapatnam are chosen for this study, due to a recorded number of rip current-related drowning cases observed during the past decade. Few experiments were conducted during pre- and post-monsoon seasons of 2018. Drifters work on the Lagrangian principle, where they measure the current velocities along their paths driven by the surface currents. Error analysis of drifter measurements showed that they are capable of resolving surf zone motions very accurately. Strong rip currents were observed in few locations in the study area, where at times current velocities reached ~1 ms⁻¹. Also, Rhodamine-B dye was released into the rip current prone zones along with the drifters and observed that the dye patches also followed the drifters. From these experiments, it has been observed that the rip currents are relatively strong during the post-monsoon season, which could be due to the change in the beach morphology. Similar experiments with more number of drifters would help in understanding rip current dynamics and would help in reducing rip current drowning in the beaches.

Research highlights

• GNSS based drifters have been designed, developed and field-tested to measure rip currents in the surf zone.

• Post-Processing Kinematic (PPK) resulted in position estimates with centimeter level accuracy.

• The drifters are capable to resolve the surf zone motions more accurately in the order of greater than 0.02 ms⁻¹.

• Several drifter deployments and Rhodamine-B dye experiments were carried out at RK and Rushikonda Beaches to measure the dangerous rip currents and coastal currents.

中文翻译：

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印度东海岸维沙卡帕特南海滩沿岸裂隙流过程的调查：基于GNSS漂流器和染料实验的研究

摘要

浪涌电流被公认为是全世界沙滩上最危险的危险之一。最少探索印度海滩来研究裂隙电流在时空上的变化性。本研究是通过利用本地开发的GNSS（全球导航卫星系统）漂流器和若丹明B染料实验来了解其动力学的首次尝试。选择维萨卡帕特南的Rama Krishna（RK）海滩和Rushikonda海滩，是因为在过去十年中观察到与激流相关的溺水案件的记录数量。在2018年的季风前后，很少进行实验。漂流者采用拉格朗日原理进行工作，在拉格朗日原理中，他们测量由地表水流驱动的沿路径的流速。漂移测量的误差分析表明，它们能够非常准确地解决冲浪区运动。在研究区域的几个地方都观察到了强大的裂隙电流，在这些地方有时流速达到〜1 ms^-1。此外，若丹明-B染料与漂流液一起被释放到易撕裂的易带区域，并观察到染料斑块也跟随漂流液。从这些实验中，已经观察到季风后季节的裂谷电流相对较强，这可能是由于海滩形态的变化。使用更多数量的漂流器进行的类似实验将有助于了解裂隙电流动态，并有助于减少海滩中的裂隙电流淹没。

研究重点

• 已经设计，开发了基于GNSS的漂移器，并对其进行了现场测试，以测量冲浪区中的裂隙电流。

• 后处理运动学（PPK）能够以厘米级的精度进行位置估计。

• 漂移器能够以大于0.02 ms ^-1的顺序更准确地解决冲浪区运动。

• 在RK和Rushikonda海滩进行了几次漂流试验和罗丹明B染料实验，以测量危险的裂隙水流和沿海水流。