Background and Objectives: Global Positioning Systems (GPS) and General Packet Radio Service (GPRS) make it possible to track surface currents at a low cost. In this paper, the details of the design and construction of an online self-recorder system to measure the lagrangian currents in the swash zone and compare it with numerical modeling results are presented. Comparing the results of the measurement device with field measurements of coastal currents shows that this drifter has good accuracy for tracking coastal currents. Although there are problems with internal shelf flows in transmitting data collected from the GPRS system, offline capability helps maintain data. Surface current measurement data were tracked off the coast of Anzali, southwest of the Caspian Sea, and several rips current cells were identified. Simultaneously, the currents simulated by the coupling of ROMS ocean models and SWAN waves showed the presence of several cells with relatively weak rip currents (less than 0.8 m/s) in the region, which is in good agreement with the information of interception drifters.
Methods: The present paper aims to present the general design of shallow water drifter for online measurement of surface current velocities including coastal and rip currents. The present study tries to evaluate the performance of shallow water drifters and use it to investigate the characteristics of rip currents in similarity to numerical models. In the second section, the physical details of the drifter design, the numerical model, the network configuration, and the induction forces are presented. In the third section, the results of flow modeling are compared with field measurements performed in the coastal swash zone of the eastern part of Bandar Anzali located in Gilan province, and joint processes are discussed.
Findings: The coastal currents caused by the waves in the coastal swash zone on the east coast of Anzali were studied. Rip currents are formed approximately 60-100 meters apart almost all along the coast. These currents are not very strong and have a speed of less than one meter.
Conclusion:  Flow modeling in the coastal area indicates the existence of several rip current cells that the path intercepted by drifters has also confirmed their existence. Although these currents are not so strong, they can be detected at distances between 30 and 60 meters. Most of these rip currents have offshore direction and have been less affected by coastal currents. Hence, the path of the drifters indicates that under normal wind conditions from the northwest, the surface currents are pushed to the east and rotate due to the shoreline. Under east wind conditions, surface currents develop primarily from east to west.