Deepesh Machiwal

Modeling Short-Term Spatial and Temporal Variability of Groundwater Level Using Geostatistics and GIS

Continuous depletion of groundwater levels from deliberate and uncontrolled exploitation of groundwater resources lead to the severe problems in arid and semi-arid hard-rock regions of the world. Geostatistics and geographic information system (GIS) have been proved as successful tools for efficient planning and management of the groundwater resources. The present study demonstrated applicability of geostatistics and GIS to understand spatial and temporal behavior of groundwater levels in a semi-arid hard-rock aquifer of Western India. Monthly groundwater levels of 50 sites in the study area for 36-month period (May 2006 to June 2009; excluding 3 months) were analyzed to find spatial autocorrelation and variances in the groundwater levels. Experimental variogram of the observed groundwater levels was computed at 750-m lag distance interval and the four most-widely used geostatistical models were fitted to the experimental variogram. The best-fit geostatistical model was selected by using two goodness-of-fit criteria, i.e., root mean square error (RMSE) and correlation coefficient (r). Then spatial maps of the groundwater levels were prepared through kriging technique by means of the best-fit geostatistical model. Results of two spatial statistics (Geary’s C and Moran’s I) indicated a strong positive autocorrelation in the groundwater levels within 3-km lag distance. It is emphasized that the spatial statistics are promising tools for geostatistical modeling, which help choose appropriate values of model parameters. Nugget-sill ratio (<0.25) revealed that the groundwater levels have strong spatial dependence in the area. The statistical indicators (RMSE and r) suggested that any of the three geostatistical models, i.e., spherical, circular, and exponential, can be selected as the best-fit model for reliable and accurate spatial interpolation. However, exponential model is used as the best-fit model in the present study. Selection of the exponential model as the best-fit was further supported by very high values of coefficient of determination (r2 ranging from 0.927 to 0.994). Spatial distribution maps of groundwater levels indicated that the groundwater levels are strongly affected by surface topography and the presence of surface water bodies in the study area. Temporal pattern of the groundwater levels is mainly controlled by the rainy-season recharge and amount of groundwater extraction. Furthermore, it was found that the kriging technique is helpful in identifying critical locations over the study area where water saving and groundwater augmentation techniques need to be implemented to protect depleting groundwater resources.

GIS-based assessment and characterization of groundwater quality in a hard-rock hilly terrain of Western India

The growing population, pollution, and misuse of freshwater worldwide necessitate developing innovative methods and efficient strategies to protect vital groundwater resources. This need becomes more critical for arid/semi-arid regions of the world. The present study focuses on a GIS-based assessment and characterization of groundwater quality in a semi-arid hard-rock terrain of Rajasthan, western India using long-term and multi-site post-monsoon groundwater quality data. Spatio-temporal variations of water quality parameters in the study area were analyzed by GIS techniques. Groundwater quality was evaluated based on a GIS-based Groundwater Quality Index (GWQI). A Potential GWQI map was also generated for the study area following the Optimum Index Factor concept. The most-influential water quality parameters were identified by performing a map removal sensitivity analysis among the groundwater quality parameters. Mean annual concentration maps revealed that hardness is the only parameter that exceeds its maximum permissible limit for drinking water. GIS analysis revealed that sulfate and nitrate ions exhibit the highest (CVxa0>xa030%) temporal variation, but groundwater pH is stable. Hardness, EC, TDS, and magnesium govern the spatial pattern of the GWQI map. The groundwater quality of the study area is generally suitable for drinking and irrigation (median GWQIxa0>xa074). The GWQI map indicated that relatively high-quality groundwater exists in northwest and southeast portions of the study area. The groundwater quality parameter group of Ca, Cl, and pH were found to have the maximum value (6.44) of Optimum Index factor. It is concluded that Ca, Cl, and pH are three prominent parameters for cost-effective and long-term water quality monitoring in the study area. Hardness, Na, and SO4, being the most-sensitive water quality parameters, need to be monitored regularly and more precisely.

Exploring hydrogeology and groundwater dynamics in a lateritic terrain of West Bengal, India, under limited data conditions

This study aimed at investigating hydrogeology and groundwater dynamics in a lateritic terrain of West Bengal, India, under limited data conditions. A field setup was developed comprising six observation wells, two on-farm reservoirs and three artificial excavations. Groundwater levels, groundwater quality and water levels of surface water bodies were monitored during 2003–2005 period. Regression and correlation analyses of groundwater levels with rainfall and surface water levels were performed to study rainfall–groundwater dynamics and surface water–groundwater interaction. Depth-wise geologic samples of six sites were subjected to grain-size analysis (GSA) and stratigraphy analysis. Hydraulic conductivities (K) of subsurface formations at different depths were estimated by three GSA models, and finally groundwater recharge was estimated. Stratigraphy analyses revealed that besides shallow aquifers, deep confined aquifers of 5–16xa0m thickness exist at 54–96xa0m depths in the study area. Significant correlation of groundwater levels with the water levels in excavations and the ‘potential recharge’ of 1.90–2.99xa0cm/day from excavations indicate that the excavations can serve as promising low-cost recharge structures for augmenting groundwater resources. Nitrate concentration in the groundwater beyond maximum permissible limit at most sites renders it unsuitable for drinking purpose. Furthermore, the Hazen, Harleman, and Alyamani and Sen models yielded reasonable K values of subsurface formations. Average hydraulic conductivity and transmissivity values of the deep aquifer system vary from 3 to 129 and 27 to 1161xa0m2/day, respectively, which suggest significant aquifer heterogeneity. Seasonal groundwater recharge in the study area was found to be in the range of 4.32–15.24xa0cm.