Exploratory modelling of wind-generated wave and current bottom stress and potential for sediment resuspension in small lakes

Although lakes are generally considered to function as long-term sediment sinks, remobilisation of bottom sediments can be significant and has implications for water quality and palaeoenvironmental analysis of lake sediment records. Wind-waves and wind-generated currents are the most important drivers of sediment resuspension but the complexity of their interaction and their intermittent nature complicate direct observation of these processes. This paper demonstrates a hybrid approach that combines a three-dimensional (3D) community hydrodynamic model (FVCOM) with a parameterised fetch-limited wind wave model to simulate the relative proportions of the lake bed subject to sediment resuspension under different meteorological conditions. Model validation and testing is undertaken for a small upland lake exposed to strong wind forcing. A series of exploratory model experiments indicate the dominance of wind-wave stresses over flow current stresses for wind speed $\le$ 12 m s${}^{-}1$. Accordingly, the ratio between wind-wave stresses and current stresses can be around 15 for low wind speeds, but this ratio tends non-linearly to 1 when wind speed increases because of the faster growth of current stresses. The analysis of wind direction scenarios under typical wind speed conditions indicate that wind waves would resuspend sediments over narrow downwind zones along the shores. At different depth ranges, wind-waves are only able to resuspend sediments in areas less than about 5 m in depth, whereas for current-induced stresses, the resuspended area is more extensive for intermediate depths (from 5 m to 15 m).