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Research article - Peer-reviewed, 2021

Variable Physical Drivers of Near-Surface Turbulence in a Regulated River

Guseva, S.; Aurela, M.; Cortes, A.; Kivi, R.; Lotsari, E.; MacIntyre, S.; Mammarella, I; Ojala, A.; Stepanenko, V; Uotila, P.; Vaha, A.; Vesala, T.; Wallin, M. B.; Lorke, A.

Abstract

Inland waters, such as lakes, reservoirs and rivers, are important sources of climate forcing trace gases. A key parameter that regulates the gas exchange between water and the atmosphere is the gas transfer velocity, which itself is controlled by near-surface turbulence in the water. While in lakes and reservoirs, near-surface turbulence is mainly driven by atmospheric forcing, in shallow rivers and streams it is generated by bottom friction of gravity-forced flow. Large rivers represent a transition between these two cases. Near-surface turbulence has rarely been measured in rivers and the drivers of turbulence have not been quantified. We analyzed continuous measurements of flow velocity and quantified turbulence as the rate of dissipation of turbulent kinetic energy over the ice-free season in a large regulated river in Northern Finland. Measured dissipation rates agreed with predictions from bulk parameters, including mean flow velocity, wind speed, surface heat flux, and with a one-dimensional numerical turbulence model. Values ranged from similar to 10-10m2s-3 to 10-5m2s-3. Atmospheric forcing or gravity was the dominant driver of near-surface turbulence for similar fraction of the time. Large variability in near-surface dissipation rate occurred at diel time scales, when the flow velocity was strongly affected by downstream dam operation. By combining scaling relations for boundary-layer turbulence at the river bed and at the air-water interface, we derived a simple model for estimating the relative contributions of wind speed and bottom friction of river flow as a function of depth.

Keywords

river; turbulence; gas exchange; wind

Published in

Water Resources Research
2021, volume: 57, number: 11, article number: e2020WR027939
Publisher: AMER GEOPHYSICAL UNION

Authors' information

Guseva, S.
University of Koblenz and Landau
Aurela, M.
Finnish Meteorological Institute
Cortes, A.
University of California Santa Barbara
Kivi, R.
Finnish Meteorological Institute
Lotsari, E.
University of Eastern Finland
Lotsari, E.
University of Turku
MacIntyre, S.
University of California Santa Barbara
Mammarella, I
University of Helsinki
Ojala, A.
University of Helsinki
Stepanenko, V
Lomonosov Moscow State University
Uotila, P.
University of Helsinki
Vaha, A.
University of Helsinki
Vesala, T.
University of Helsinki
Vesala, T.
Yugra State University
Uppsala University
Swedish University of Agricultural Sciences, Department of Aquatic Sciences and Assessment
Lorke, A.
University of Koblenz and Landau

UKÄ Subject classification

Oceanography, Hydrology, Water Resources
Climate Research

Publication Identifiers

DOI: https://doi.org/10.1029/2020WR027939

URI (permanent link to this page)

https://res.slu.se/id/publ/115035