Accurate estimation of the groundwater budget requires good estimate of flux across the boundary of a region. Different methods and techniques are available to estimate recharge to groundwater; however methods for estimation of flux across boundaries are not available. The present article represents a GISbased methodology to estimate the groundwater flow rate and volume of water flux across the boundary. Groundwater level data (pre-monsoon and postmonsoon) are used to derive detailed maps like flow direction, hydraulic gradient and velocity component perpendicular to the boundary.

The study highlights the climatic water balance, drought assessment and agricultural potentiality of Uppar Odai sub-basin located in the Southern part of India, Tamil Nadu state. The average annual precipitation in the sub-basin is 625 mm, which is much lower than the state average rainfall (970 mm). It has been observed that the intensive agricultural practices and extensive groundwater mining lead to the groundwater decline in the sub-basin. Rainfall data were collected from 1971-2011 for five rain gauge stations.