From short-term vertical ADCP measurements to continuous Side-Looking current meter monitoring in a high-latitude river

River flow conditions at high latitudes show strong seasonal variability due to changes in hydrological conditions throughout the year. During winter, ice cover reduces flow velocity. In spring, snowmelt increases discharge and often results in flooding. During summer and autumn, rainfall can cause temporary increases in discharge. High-latitude fluvial environments are particularly sensitive to climate change, which has been found to have a stronger impact in these regions than in rivers at lower latitudes. This study investigated seasonal flow dynamics in a single meander bend of the Oulankajoki River in Finland during winter, spring, and autumn over one hydrological year using an Acoustic Doppler Current Profiler (ADCP). Vertical ADCP surveys provided detailed cross-sectional velocity profiles and flow directions throughout the water column in each field campaign.

Results showed significant variation between seasons. Winter ice cover significantly reduced near-surface velocities and shifted the high-velocity core (HVC) to mid-depth, whereas in open-water conditions the highest velocities occurred closer to the surface. In open-channel conditions, peak velocities were observed in the shallow upstream and deep downstream sections of the bend, while in winter flow decelerated downstream of the bend apex.  During winter and autumn, the HVC was located near the inner bank in the upstream section of the meander bend and gradually shifted to the outer bank before the bend apex. Downstream of the apex, the HVC migrated from the outer bank toward the center of the channel. Unlike in winter and autumn, the spring flood caused the HVC to migrate from the upstream of the meander, flow directly across the point bar, and shift toward the outer bank at the apex.

The study is now being extended by integrating continuous monitoring of flow conditions using a side-looking Doppler current meter. This enables long-term, high-resolution observations, including ice-covered periods. Combining vertical and horizontal ADCP measurements is expected to provide a rare, spatially comprehensive and temporally continuous dataset. This integration enables improved characterization of flow variability and seasonal dynamics in high latitude rivers, thereby enhancing hydrological analyses and process-based modeling.