Measurements and three-dimensional simulations of flow in a shallow reservoir subject to small-scale wind field inhomogeneities induced by sheltering

Abstract

Spremberg Reservoir is a small and shallow water body where wind sheltering along steep and densely vegetated sections of the shoreline is expected to produce small-scale inhomogeneities of the wind field across the water surface. The potential impacts of these inhomogeneities on the quasi-steady circulation in the main subbasin of the reservoir are investigated in this study by means of a three-dimensional hydrodynamic model. ADCP measurement profiles at three locations are available for comparison. Agreement between characteristic features of the measurements and the simulation data cannot be achieved if uniform winds are applied as boundary conditions, but improves distinctly when sheltering effects are implemented. This is done qualitatively by means of analogy to the separation of flow across a backward fac- Aquat. Sci. 67 (2005) Aquatic Sciences ing step. For south-westerly winds, the modification of the flow tends from a three-dimensional to an essentially horizontal, one-cell circulation. The action of the wind sheltering on the flow is found to rely on (1) the addition of a curl to the background wind field and (2) the weakening of the topological moment along the windward shore. In Spremberg Reservoir the first mechanism appears to prevail for south-westerly winds. The study underlines the need for consideration of small-scale inhomogeneities of the wind field induced by sheltering as a potential source of vorticity in hydrodynamic simulations. Further investigations should be directed towards a physically founded parameterization of the actual wind stress distribution and towards quantifying lake dimensions at which such influences on the circulation pattern tend to be negligible.

Wind Shear Stress Interpolation over Lake Surface from Routine Weather Data Considering the IBL Development

“…The spatial variability of the wind stress influences strongly these motions. By studying the horizontal vorticity balance of the surface layer in Lake Kinneret and in Spremberg Reservoir, Laval et al (2003) and Rubbert and Köngeter (2005), respectively, showed that wind stress curl is a significant source of large scale horizontal vorticity with a magnitude comparable to that of the topographical curl [1,2]. Considering the spatial variability of the wind forcing they achieved improvements in simulated long wave amplitudes, phases and velocity fields.…”

Topographic effects on the thermal structure of Himalayan glacial lakes: Observations and numerical simulation of wind

“…Such a decrease in the wind velocity can weak the setup and vertical circulation as in Imja. The wind field inhomogeneity over a lake made up by the surrounding topography directly impacts the hydrodynamics (Endoh et al, 1995, Laval et al, 2003, Rubbert and Köngeter, 2005.…”

Hydrodynamic modelling and characterisation of a shallow fluvial lake: a study on the Superior Lake of Mantua

“…This causes a severe underestimation of the influence of wind on circulations under strong interacting conditions between the wind and the riverine current, e.g., for the low winds common to basins in lowland areas (Fenocchi et al, 2016). Use of 3D models, as in Rubbert and Köngeter (2005) and Anderson et al (2010), is therefore advised for these basins, also as simulation times are nowadays adequate (Fenocchi et al, 2016).…”

“…Well-mixed conditions along the water depth were assumed, as verified by field measurements (Fenocchi, 2015). In fluvial lakes, the through-flowing current provides a background turbulence, preventing stratification even under no-wind conditions, so that baroclinic effects Rueda et al, 2003) can be neglected (Rubbert and Köngeter, 2005;Anderson et al, 2010;Schimmelpfennig et al, 2012). Indeed, small temperature gradients may be present in the deepest parts during summer drought periods.…”

“…Hodges, 2014 for a list of references), fluvial lakes have received less attention (Rubbert and Köngeter, 2005;Anderson et al, 2010;Schimmelpfennig et al, 2012), so that knowledge about their circulation modes and their modelling is weaker. This paper describes the setup and application of a numerical model aimed at reproducing the significant physical features shaping circulations in the Superior Lake of Mantua, a small shallow fluvial lake in Northern Italy which hosts vast lotus flower (Nelumbo nucifera) canopies.…”