TN-32 : Evaluation of component of water balance of a river reach

Abstract

The water balance has been used for computing seasonal and geographic patterns of irrigation demand, soil moisture stress , prediction of stream flow and water tables elevations. Although, the predictions may be approximate, they are sufficiently accurate to indicate whether a scheme is hydrologically sound or not. The water balance requires that the items of supply balance the items of disposal and storage. In nature a balance is always maintained. This generally manifests itself in the form of floods, water logging, drought, etc. which may be detrimental to human activities.

The water balance of a river reach is closely interrelated with surface water and ground water. It requires quantification of inflow, outflow and storage. Some of these elements could be directly measured while others need to be estimated. There may be noticeable difference between the natural inflow and natural outflow in a river reach over periods of a month, season or an year.

It is useful to classify the river reach into alluvial or non-alluvial so that hydrologic characters can be defined and determined. Bank. storage effects have to be properly accounted. Six components (viz. precipitation, inflow from the upstream, storage, diversion, outflow, and ground water component and bank storage) have been identified and dealt with briefly in this technical note. Possible methods of evaluation of each one of these are mentioned.