Behavior of cold water mass due to water surface cooling in a closed water body

In some closed water bodies with little inflow and outflow, a flow is gentle and its water quality gets worse by developing stratification. And its main dynamics of flow are circulation flow based on wind action on a water surface (mechanical disturbance) and a thermal convective flow by solar radiation, (thermal disturbance) In the present research, we focused on a closed water body where thermal turbulence was outstanding. Hydraulic experiments were conducted to investigate the behavior of the cold water mass formed around a water surface when the water surface was cooled naturally. And the difference of the behavior was investigated under coverage and no-coverage plants on a water surface. Results indicated that turbulence intensity of the cold water mass and the time scale of convection were influenced by both the Rayleigh number and coverage. The falling cycle of cold water mass was influenced by only the Rayleigh number. The falling cycle of cold water mass and development of convective a flow were also observed by the wavelet transform in the change of water temperature.