GIS-based delineation of potential recharge zones of groundwater and its validation with actual recharge in the Nangasai River Basin of Eastern India

Groundwater is one of the most significant natural resources. However, due to continuous use and over-exploitation of groundwater, this resource is under continuous threat of depletion. Under such circumstances, it is imperative to detect the possible recharge zones for assessing the groundwater scenario of the region. Identification of groundwater recharge zones is predominantly index-based and is dependent on multiple parameters which, more or less, act in tandem. This has called for the application of multi-criteria decision-making techniques (MCDMs) in this domain. The present paper is, therefore, an application of the Entropy-based MCDM as well as multiple regression techniques in assessing the potentiality of groundwater recharge in the Nangasai River Basin of eastern India. This included an integration of physiographic (relative relief, slope), drainage (drainage density, stream frequency), landuse (Normalized Difference Vegetation Index, Normalized Difference Builtup Index) and structural (lineament density) factors which influence groundwater recharge to some extent. The results of groundwater recharge potential were extracted with respect to sub-basin and village level. The model was tested with respect to its validity as the results were compared with the Central Groundwater Board derived data for actual recharge. The validity came out to be only 0.47 (47%), which was moderate. So, we looked for other factors such as potential evapotranspiration and population. Although the Receiver Operating Characteristic Curve yielded unsatisfactory results (33% validation) with potential evapotranspiration, the results were more favourable with respect to population (46% validation). Also, the spatial pattern of the actual recharge, more or less, coincided with the population pattern. This study, therefore, concludes that alongwith the physical factors, the draft and usage of groundwater plays an important role in groundwater recharge. Also, the villages in the southern part of the basin are characterized by very low recharge, in spite of considerable potentiality of recharge. So, proper planning and construction of artificial recharge structures is the need of the hour.