TN-113 : Thermal regime of lakes

Abstract

One of the most striking phenomenon of lakes is the relationship between water and temperature. Lakes have an extremely large capacity to accept hest owing to their large storage mass and high residence time. The temp.- water relationship is observed in the seasonal variations. Although most lakes in temperate region mix vertically twice a year, it is not so for tropical lakes because of the seasonal changes in temperature are less pronounced. However lakes in tropical region may also develop thermal stratification such as the one seen in Kumaun and Kashmir lakes of India.

The thermal behaviour of lakes is a complex process. It is a complex interactions of many physical processes like radiation, evaporation, advective and convecting mixing, wind induced mixing etc. These have been discussed at length. A total heat balance of the lake has also been discussed.

The study of the thermal process is important because knowledge of temperature distribution is a basic requirement for all ecological and water quality models. Temp. affects many biological and chemical processes, and affects the spread of pollution in lakes. But unfortunately in India there are no attempts to study the thermal behaviour of lakes. Apart from the Inadequate temperature data for. some Kumaun and almost no temperature data is available for any lakes. So the analysis of the thermal behaviour is Attention needs to be paid to the problem. Many describing the stratification and thermocline have

Kashmir lakes, of the Indian not possible. thermal models been developed so far but are mostly for the temperate lakes and as such can not be directly applied to the Indian conditions. However, with modification they can be applied to the Indian lakes. An approach for modelling has been presented.

The report also presents a thermal classification of lakes based on overturn and stratification. Bust since all Indian lakes do not show overturns this global scheme is not useful to thermally classify Indian lakes. A separate scheme of thermal classification needs to be formulated for Indian lakes which at present is not possible owing to the unavailability of temperature and other hydrometeorological data and the inadequacy of knowledge of total Indian lakes.