Effect of submerged vegetation on water surface geometry and air-water momentum transfer

TL;DR

This study uses detailed simulations to show that submerged vegetation smooths water surface deformations but does not change the aerodynamic roughness affecting air-water momentum transfer.

Contribution

It provides the first fully resolved multiphase simulation of submerged vegetation effects on water surface geometry and momentum exchange, with implications for boundary-layer modeling.

Findings

Vegetation submerged for four times its height smooths water surface deformations.

Surface regularization does not alter the equivalent roughness perceived by airflow.

Results inform wave mitigation strategies and atmospheric boundary-layer models.

Abstract

Understanding how submerged vegetation modifies the water surface is crucial for modeling momentum exchange between shallow waters and the atmosphere. In particular, quantifying its impact on the equivalent aerodynamic roughness of the water surface is essential for improved boundary-layer parameterization in oceanic and atmospheric models. In this Letter, we present fully resolved multiphase simulations of gravity-driven flow over a fully submerged vegetated bed, capturing the coupled dynamics of air, water, and individual plant stems, under quasi-realistic conditions (the air/water viscosity ratio is real, while the density ratio is reduced tenfold). Our results show that vegetation submerged for four times its height regularizes the water surface suppressing strong deformations and homogenizing streamwise-propagating wave fronts along the transversal direction. Despite these alterations, the equivalent roughness perceived by the overlying air flow remains unchanged. These findings clarify vegetation-surface interactions and provide quantitative insights for nature-based wave mitigation strategies and atmospheric boundary-layer modeling.