Response of a Small River Plume on Wind Forcing

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.

Lateral Border of a Small River Plume: Salinity Structure, Instabilities and Mass Transport

“…For this purpose, we performed five field surveys at the small Kodor and Bzyp river plumes located at the eastern part of the Black Sea in 2018-2022. This study continues our previous research of small river plumes in the Black Sea focused on the structure of small plumes [2,3,57], influence of wind forcing and river discharge variability on small plumes [4,58,59], generation of internal waves in river plumes [6,60], influence of small plumes on water quality and marine pollution [14,61].…”

“…Five field surveys described in this study were performed at the buoyant plumes formed by the Kodor and Bzyb rivers in the eastern part of the Black Sea (Figure 1). General characteristics of the Kodor and Bzyb plumes and the ambient saline sea are described in detail by Osadchiev et al [2][3][4]6]. The information about all field surveys analyzed in the study is summarized in georeferenced by direct projection into an earth-based Cartesian coordinate system using GPS and altimetry data from the quadcopter.…”

“…These gradients are especially strong at plumes formed by small rivers, which have small spatial scales and small freshwater residence time equal to hours and days [1][2][3]. In particular, horizontal (3-4 salinity units/m [2,4]) and vertical (5-6 salinity units/m [5,6]) salinity gradients observed at the outer borders of small plumes are among the largest reported in the World Ocean.…”

Structure and variability of the Pechora plume in the southeastern part of the Barents Sea

“…This feature could be explained by smaller depth (4-8 m) and area (6 000 -36 000 km 2 ) of the Pechora plume as compared to large river plumes mentioned above (with depths >10 m and areas >100 000 km 2 ). On the other hand, the response rate of small river plumes with depths of 1-2 m and area of 1-10 km 2 is equal to several hours (Pinones et al, 2005;Korotkina et al, 2011;Korotkina et al, 2014;Qu and Hetland, 2019;Osadchiev et al, 2020d;Osadchiev et al, 2021d), which is much smaller than that for the Pechora plume. We want to highlight, that these results were obtained using in situ and satellite data and should be considered for numerical modeling of these river plumes.…”

Modelling the interannual variability of Maipo and Rapel river plumes off central Chile

“…Normally, the river plume flows northward along the Washington coast, but in spring-summer the upwelling-favorable winds and coastal circulation forces the plume farther south and offshore off Oregon (Hickey et al, 2005;. In general, the role of the wind forcing is enhanced on small river plumes (Osadchiev et al, 2021;Basdurak and Largier, 2022), which is the case for most river outflows along central-southern Chile .…”