Groundwater recharge has been estimated using a simple water balance approach known as Water Level Fluctuation Methodology, which is directly implemented in GIS on a cell basis. Further, impact of urbanization on groundwater resources (recharge and quality) have been studied using overlay analysis of interrelated themes in GIS.
The present study is useful in identifying the potential threats to groundwater of area, and to generate a water resource database for overall development on a sustainable basis, which can help urban planners and decision makes for the policy decisions.
Result
Urban growth
Urban growth dynamics of the Ajmer city has been evaluated using the classified satellite data of 7 years, i.e. 1989, 1991, 1994, 1997, 2000, 2002, and 2005. Spatial and temporal growth of Ajmer urban area has been shown in Fig. 1 with GIS. The rate of development of land in Ajmer is outstripping the rate of population growth. Between 1989 and 2005, population in the region grew by 32.2% while the land development increased by 74.5%, more than two times the rate of population growth. This implies that the land is being used for urbanization at a faster rate, which indicates that per capita consumption of land has increased exceptionally over last decades.
Fig. 1 Urban growth of the Ajmer city 1989 to 2005
Groundwater recharge
An attempt has been made to assess the net effect of urbanization on groundwater recharge through estimating the groundwater recharge from the impervious area only, which has not been added to the groundwater on account of urbanization.
Further, overlay analysis has been carried out to interpret the urbanization impact on groundwater recharge. Recharge due to rainfall will definitely reduce in proportion to the impervious surfaces. As urbanization taking place pervious areas become impervious, and subsequently rainfall recharge reduces.
However, in some areas recharge may increase due to leakages from the water supply distribution systems and wastewater generated subsequently, since it normally comprises of more than 80% of gross water production (Ajmera 2000). This type of recharge will increase with urbanization but it may have adverse effect on the quality.
Fig. 9 GIS-Groundwater depletion between years 1991 and 2005 (Negative sign shows increase in level)
Groundwater quality
In urban residential areas, without or with incomplete coverage by sewerage (most of the urban areas in developing countries including Ajmer city), seepage from un-sewered sanitation system such as septic tanks, soakpits and latrines, probably represent the most widespread and serious source of diffuse pollution.
For groundwater, the immediate concern from on-site sanitation systems is a risk of direct migration of pathogenic bacteria and viruses to underlying aquifers and neighboring groundwater sources.
The fractured Gneiss and Schist aquifer in Ajmer city is especially vulnerable in this respect and widespread and gross bacteriological contamination of the urban groundwater was observed; faecal coliform counts in excess of 300 per 100 ml were not uncommon in samples from shallow wells (using GIS).
Fig. 11 Decline in groundwater quality (increase in concentration) from 1992 to 2003
Original article:
Mahesh K. Jat, Deepak Khare and P. K. Garg
The Environmentalist, Volume 29, Number 1 / March, 2009
The Environmentalist, Volume 29, Number 1 / March, 2009
