Response of a Small River Plume on Wind Forcing

Alexander Osadchiev,Roman Sedakov,Alexandra Barymova

doi:10.3389/fmars.2021.809566

Abstract

Wind forcing is the main driver of river plume dynamics. Direction and magnitude of wind determine position, shape, and size of a river plume. The response of river plumes on wind forcing was simulated in many numerical modeling studies; however, in situ measurements of this process are still very scarce. In this study, we report the first direct measurements of frontal movement of a small river plume under variable wind forcing conditions. Using quadcopters, we performed nearly continuous daytime aerial observations of the Bzyb river plume located in the non-tidal Black Sea. The aerial remote sensing was accompanied by synchronous in situ measurements of wind forcing. We assessed spreading patterns of the plume and evaluated movement velocity of its outer border with unprecedentedly high spatial (∼10 m) and temporal (∼1 min) resolution, which was not available in previous studies based on in situ measurements and satellite observations. Based on the collected data, we evaluated the time of response of plume spreading dynamics on changes in wind forcing conditions. The advection velocity of the outer plume border shows linear relation to wind speed with very small response time (10–20 min). The reversal between upstream/downstream plume spreading occurs during several hours under moderate wind forcing conditions. These reversals involve only near-field part of the plume, which cause detachment of the far-field part of the plume. The obtained results are crucial for understanding and simulating spreading dynamics of small river plumes worldwide.

Highlights

Wind forcing and river discharge rate are two major factors that govern spreading of river plumes
This work is focused on evaluation of response of a small river plume on variable wind forcing
We studied the Bzyb river plume located in the eastern part of the Black Sea

Summary

INTRODUCTION

Wind forcing and river discharge rate are two major factors that govern spreading of river plumes. The majority of these works were based on numerical modeling of river plumes under different wind forcing conditions Studies of this process based on in situ observations are still very scarce due to complexity of simultaneous thermohaline and velocity measurements at various plume regions with highly variable properties, positions, and circulation patterns. In situ measurements of different plume characteristics (vertical structure, location of outer front, spreading direction, inner circulation, etc.), which change in response to changes in wind forcing conditions, are crucial for general understanding of spreading and mixing of river plumes. The exact coordinates of the river mouth and sea shoreline at the georectified imagery were validated against the Sentiunel-2 satellite image (with 10 m spatial resolution) taken during the period of field work This is an important issue due to regular morphologic changes induced by order to obtain accurate georeferencing using multiple onshore ground control points, the observed area should partly cover the coast.

RESULTS

DISCUSSION AND CONCLUSION

DATA AVAILABILITY STATEMENT