SR-37 : Water balance of lakes

Abstract

Lake Water Balance relationships forms the basis for rational deterministic hydrological forecasting models and are necessary to harness, develop and manage lake water. Assessment of the causes of lake deterioration and the success of amelio-rative strategies depend on nutrient budgeting and water budgeting is basic to calculate nutrient budgeting. The available models of lake water balance with concomitant nutrient budgeting are described. The various components of water balance, their web of interdependences and interactions, errors and difficulties involved for various types of lake are discussed at length. It has been found that the energy budget method is the most accurate method of calculating evaporation with least error. Groundwater component especially for a closed lake if estimated as a residual, could differ from an independent estimate of groundwater beyond permissible error. For surface water inflow, the non-channelized flow which are difficult to measure/estimate is the main source of error. Szesztay's classification of lakes on the basis of main water balance components is the only approach so far available to classify lakes on the basis of hydrologic indices and is recommended to be adopted for Indian lakes. Examples of water balances of lakes in equatorial tropics are included as the environmental conditions are close to Indian context. Differences of lake processes for large and small lake and their implications and effect in water balance of a lake is discussed and most of our lakes could be taken as small lakes for their hydrologic behaviour and for water balance study.