The Effects of Basin Dimensions on the Seasonal Depth of Thermocline and Temperature of Hypolimnion in Small Lakes

A model is presented for calculation of the seasonal thermocline depth and the temperature of hypolimnion of small lakes. The model input data are the daily means of the surface water temperature (at depth of 0.5 m), incoming global radiation, and wind velocity. The lake parameters are the maximum depth, surface area, a parameter (m) describing the lake bathymetry, and diffuse light attenuation coefficient. The model is formed of two connected parts. 1) A generally used differential equation for the thermocline depth; and 2) A temperature model where the hypolimnion is divided into two parts: a lower non-stratified part with logarithmic velocity profile and an upper part with mixing controlled by buoyancy. The first model has three parameters and the second one has two, determined by calibration with 31 lakes. The surface areas of these lakes varied between 0.004 and 13.6 km 2 , and the maximum depths ranged between 5 and 85 m. The combined model was tested with independent data from three lakes with time series of thermocline depth and hypolimnion temperature.