TN-99 : Behaviour of different types of lakes and their effect and relationship on with the catchment hydrology

Abstract

The knowledge of interaction of lake and the nearby catchment is important to plan proper use and conservation of lake water. Lakes contain over 95% of the world's surface supply of fresh liquid water. A lake is easy to visualise because of its definite boundary unlike other types of storage in hydrologic cycle. But, the matter of a precise hydrologic definition of a lake has received insufficient attention and a proper definition of a lake does not exist. Some termed lake as 'Wide places in river'. But this is not true. From the geologic view-point a lake is a ephemeral landscape and consists of two distinct parts - the basin and the water body. Both should be taken care of in any workable definition of lake.

Hydrologic cycle conceptualise some short and some long devious paths in terms of time and space to circulate water. Lake with its definite boundaries is one of such paths which participates and responds sensitively to regional changes in climate and changes in its adjoining catchment whether occurring slowly by natural means or rapidly due to development activities.

Because of storage of large mass of water and high residence time , it moderates flood and climatic factors in the region. Also deforestation, conversion of grassland to cropland, intensification of agricultural production etc. reduce evapotranspiration thereby affecting runoff and rates of erosion and subsequent siltation of lakes. Due to relative lack of motion of water, lake acts as a potential sediment trap of the nature. Continued erosion will eventually destroy the water holding capacity of the lake. The process is often hastened by the growth of aquatic plants and organic matter due to intake of nutrients from the nearby area. Various physical, chemical and biological inputs affect the quality, quantity and regimen of lake water. Lake is a dynamic system and the hydrology of a lake at a given time is the sumtotal of complex, interdependent inter-actions of all the inputs and outputs to lake from atmosphere, hydrosphere and lithosphere.