Mixing by wind-induced flow and thermal convection in a small, shallow and stratified lake

Thermal stratification is one of the important features in closed water bodies, which primarily depend on meteorological conditions, and has strong impact on the ecological environment in lakes or reservoirs. Data monitored in 3 days were analyzed for factors that affect heat mixing processes to examine the diurnal stratification cycles in the Shikinawa Lake, a study area in Fukuoka prefecture, Japan. We found that wind speeds and directions played an important role in the thermal mixing in the lake. High solar heating mainly caused stratification state, but with less effect under stronger wind action. Development of mixed layer depth in a natural lake due to wind-induced flow and thermal convection were calculated. Functional relationships between entrainment rate and Richardson number or Wedderburn number were found and represented in this paper. Besides, heats exchanged at the air-water interface and energy stored in the water column were also analyzed and discussed.