Rip currents in the southern Baltic Sea multi-bar nearshore zone

Abstract

Rip currents in the southern Baltic Sea coastal zone are one of the most incompletely known and least explored hydrodynamic phenomena. As they are rare, discussion on their nature, their contribution to the complex pattern of nearshore currents, and their effect on, inter alia, the seafloor transformations is still on-going. Observations made during this study confirmed the occurrence of rip currents at the southern Baltic Sea shore. During field surveys in 2011–2013, Lagrangian measurements taken using novel GPS-tracked drifters revealed several flow events with features characteristic of rip currents. At the same time, numerical calculations produced a three-dimensional wave-current field in the surf zone. Both the measurements and numerical modelling made it possible to follow the rip current dynamics in the area of study and to compare the rip currents observed with those known from other reflective coasts. In addition, wave action-related and bathymetric conditions conducive to the rip current emergence were identified, and the relationship between the rip current velocity, wave regime and local seafloor morphology was explored. The results confirm the theory of rip currents at dissipative shores emerging at the prevalence of fairly flat long waves. Such conditions are typical at swells, i.e., during storm abatement.