Integrated assessment of groundwater resources in a semi-arid watershed of South India: implications for irrigated agriculture

Groundwater resources play a vital role in the socio-economic development of Andipatti watershed—a semi-arid region situated in Theni district of Tamil Nadu, South India. Due to a short spell of rainfall (40 days in a year) and ephemeral nature of streams, the quantum of surface water in the watershed is not found to cope with the agricultural requirements and as a result, more emphasis is given to the exploitation of groundwater. The haphazard utilization of groundwater for agricultural practices affects the quantum and quality of groundwater severely. The present study is attempted to assess the potential, level, quality, suitability and utilization level of groundwater resources in an integrated manner. Groundwater potential of the study area is assessed using resistivity, well yield and dug well data. The groundwater potential zones exhibit a strong relationship with land use pattern i.e. poor potential zones is marked by fallow lands. The spatial pattern of groundwater level and quality is examined using the data collected from 34 open wells across the study area during pre-monsoon and post-monsoon seasons. The groundwater level of the watershed varies from 0.5 to 47 m with an average fluctuation of 2 to 4 m. The long-term fluctuations of the groundwater level showed that there is a cyclic trend depending upon the rainfall pattern of the watershed. However, the declining trend of groundwater level noticed especially in the upper part of the watershed. The suitability of groundwater for irrigated agriculture is examined using the concentrations and indices of chloride, magnesium ratio, sodium adsorption ratio, residual sodium carbonate, soluble sodium percentage, and permeability index of the collected groundwater samples. A method formulated by the US Salinity Laboratory is also attempted for the classification of groundwater quality zones. In order to ascertain and suggest sustainable planning measures, utilisation pattern of groundwater is assessed on a micro-watershed scale. The spatial distribution of analyzed parameters shows the suitability of groundwater for irrigation and associated impacts in the watershed.