IMPACT OF URBANIZATION ON GROUNDWATER IN LUCKNOW AREA, INDIA

Abstract

Urbanization often leads to an increase in groundwater demand due to expansion in urban areas and accompanied land use changes. Studies based on satellite gravity observations indicated that Northern India lost about 109 km3 of groundwater between 2002 and 2008 leading to a decline in water table to the extent of 0.33 meters per annum. The focus of the present study was to assess the effect of urbanization on groundwater in terms of groundwater vulnerability to pollution and groundwater resources, using satellite observations, Geographical Information System (GIS) and ground-based investigations. Lucknow City, the capital of Uttar Pradesh, of North India was taken as the study area. Recently available methods for assessment of groundwater vulnerability to pollution were reviewed and a new (modified) method suitable for an urbanized environment was developed. The results were validated by comparing with the observed groundwater quality characteristics. The groundwater depletion trends were estimated using data obtained from Gravity Recovery and Climate Experiment (GRACE) and Global Land Data Assimilation System (GLDAS). The study area, situated in Ganga-Gomti interfluve, witnessed an unprecedented growth in water demand during the last few decades. The groundwater samples of the study area collected during pre-monsoon (May, 2011) and post-monsoon (November, 2011) seasons representing the shallow and deeper aquifers were analyzed for various physico-chemical parameters, such as pH, Electrical Conductivity (EC), Total Dissolved Solids (TDS), major cations (Ca2+, Mg2+, Na+, K+), major anions (HCO3 -, Cl-, SO4 2-, NO3 -, F-) and trace elements (As, Hg, Fe, Cr, Zn, Pb, Mn). The groundwater quality in the study area did not indicate much variation between premonsoon and post-monsoon seasons. Nitrate (NO3 -) concentration is found to be beyond desirable limit in ~70% groundwater samples indicating to inputs from sewer systems. Amongst the trace elements, acceptable limits of mercury (Hg) and iron (Fe) are violated in many samples. The groundwater vulnerability assessment was carried out using DRASTIC (D=Depth to water table, R=Recharge, A=Aquifer media, S=Soil media, T=Topography, I=Impact of vadose zone, C=Hydraulic conductivity) method. A new (modified) DRASTIC model, called DRASTICA, was developed by inclusion of a new parameter ‘impact of anthropogenic activities’ (A). The comparison of DRASTIC and DRASTICA model based groundwater vulnerability/risk maps with the observed groundwater quality indicated that the DRASTICA model performs better than the traditional DRASTIC model in urbanized environment. Sensitivity analysis indicated that anthropogenic impact (A) and depth to water table (D) largely influenced the groundwater iii vulnerability/ risk to pollution, thereby signifying that anthropogenic influence needs to be appropriately addressed. Grace is unique in its ability to monitor changes in land water storage at all levels- from the top of the plant canopy to the base of the deepest aquifer and allow us to directly monitor regional changes in stored water. The seasonal and yearly hydrologic signals acquired by GRACE and simulated soil moisture from GLDAS were studied in the entire State of Uttar Pradesh with an emphasis on the Lucknow district for assessing the mass change due to groundwater withdrawal from aquifers. Time series analysis of terrestrial water storage (TWS) obtained from GRACE, soil moisture from GLDAS, and rainfall data indicated volumetric groundwater storage loss of about 0.37 km3 in Lucknow District. The results compared very well with the observed water table trend. The study presented a novel approach to holistically understand and assess the effect of urbanization on groundwater by integrating the multi-source datasets and validating the results with ground observations. The results will help water resource managers and urban authorities in taking up appropriate remedial measures to protect groundwater reserves from further deterioration both in terms of quality and quantity. Proper sewerage system; artificial recharge of groundwater, especially through roof water harvesting structures, in the high and very high vulnerable/ risk zones and high-exploitation zones; conjunctive use of surface and groundwater resources in shallow water table areas are some of the suggested measures.