Analysis of Surface Currents during Flood and Ebb Tides Using the LSPIV Method in the Rokan River Estuary

Abstract

The Rokan River Estuary is a transitional zone with complex hydrodynamics shaped by the interaction of river discharge, tidal forces, and bed morphology, making reliable surface current data essential for coastal management and navigation safety. This study aimed to analyze the characteristics and velocity of surface currents during flood and ebb tide conditions in the Rokan River Estuary using the Large-Scale Particle Image Velocimetry (LSPIV) method based on UAV drone video imagery, and to evaluate its agreement with current meter measurements. The research was conducted in February 2025 through a quantitative descriptive-spatial field survey; video data were processed using pyOpenRiverCam and validated via linear regression, correlation coefficient (R), coefficient of determination (R²), RMSE, and MAE. Results showed surface current velocities ranging from 0–2 m/s, flowing relatively uniformly toward the southwest–west during ebb tide following the river flow, while during flood tide the current became more variable toward the southeast–east due to seawater intrusion. Validation revealed a positive but weak relationship between LSPIV and current meter data, with better accuracy during the flood phase (R=0.362; R²=0.131; RMSE=0.309) than the ebb phase (R=0.242; R²=0.058; RMSE=0.407). The UAV-based LSPIV method proved to be a promising, efficient, and non-contact alternative for surface current measurement, supporting sustainable estuarine hydrodynamic studies.