How Turbulence Regulates Evaporation from Flowing Water Surfaces

Abstract: The role of turbulence in heat and mass exchange across flowing water surfaces remains poorly understood.  Insights from oceanic wavy surfaces offer useful analogies [1], yet, fundamental differences in directional hydrodynamics and near-surface turbulence limit their direct applicability to flowing rivers and streams. Evidence suggests that intermittent turbulence-interfacial interactions observed from rapid IR imagery of flowing surfaces regulate evaporation rates. A laboratory flume with adjustable bottom roughness and flow configurations was used to generate distinct turbulent and mixing regimes [2]. Synchronized high-speed infrared surface thermography and vertically resolved micro-thermocouple measurements captured the transient evolution of the thermal skin layer and near-surface eddy diffusion characteristics. Preliminary results from shallow-water flows indicate that increased turbulence intensity, reflected in surface thermal fluctuations enhance evaporation rates relative to placid surfaces under similar conditions. Surface renewal theory was employed to quantify the contribution of turbulent renewal events on exchange rates across contrasting flow regimes. Results provide new insights into turbulence-driven interfacial processes and offer a mechanistic basis for improving representations of evaporation dynamics across variable flow conditions in riverine systems.

Reference
[1] Gerbi, G. P., Trowbridge, J. H., Terray, E. A., Plueddemann, A. J., & Kukulka, T. (2009). Observations of turbulence in the ocean surface boundary layer: Energetics and transport. Journal of Physical Oceanography, 39(5), 1077-1096.
[2] Hou, L., Aminzadeh, M., Or, D., Patzke, J., Fröhle, P., & Shokri, N. (2025). Evaporation dynamics from flowing water surfaces (No. EGU25-2716). Copernicus Meetings.