Implementation of a 3D ocean model to understand upland lake wind-driven circulation

Abstract

A community numerical ocean model is used to extend the understanding of winddriven circulation in small upland lakes. A 3D model of a case study lake (Llyn Conwy, Wales, UK) is calibrated against measured velocity profiles via adjustment of the bottom roughness coefficient. Validation against a separate set of measured velocity profiles confirms the ability of the model to resolve key features of the flow field. Sensitivity analysis shows that the velocity field responds rapidly to changes in the wind forcing. Analysis of the gross circulation using Empirical Orthogonal Functions reveals a persistent two-gyre circulation pattern in the upper half layer of the water column driven by the interaction of wind and bathymetry. At the bottom, the flow is characterised by locally strong currents and analysis of vertical circulation over short time scales shows strong currents in the deepest parts of the lake basin and the responsiveness of the water column to changes in wind speed and direction. Even in small lakes, the assumption of uniform wind stress across the water surface is not always justified and topographic sheltering or other catchment roughness effects give rise to heterogeneity in the wind field. An idealized experiment for the case study lake shows that differences in circulation emerge if the wind stress is allowed to vary across the lake. Energetic wind forcing in upland areas can drive an energetic lake circulation that has important implications for mixing and sediment dynamics. 3D numerical modelling of winddriven circulation should be more widely used to provide insights into physical limnology to support a wide range of ecological, biogeochemical and palaeoenvironmental studies.

Numerical Investigation of the Effects of Aquatic Vegetation on Wind-Induced Wave and Current Characteristics in Shallow Lakes

“…Scholars have used the numerical simulation method to simulate the influence of vegetation on the wind-induced current in the shallow lakes, but these studies are based on the two-dimensional hydrodynamic model (Xu et al, 2018) and use the method of increasing local Manning coefficient to simulate the vegetation resistance (Li et al, 2020), so it is unable to describe the submerged vegetation effect and the three-dimensional characteristics of shallow lake flow field. In recent years, several open-source three-dimensional models which allow custom editing to study the complex interactions between vegetation and water flow have been developed, such as FVCOM (Morales-Marín et al, 2017), SCHISM (Zhang et al, 2019b), and ROMS (Beudin et al, 2017). These models use the method of adding body resistance into momentum equations to simulate the resistance of vegetation and are widely used to study the attenuation of vegetation on coastal storm surge (Zhang et al, 2019a).…”