Comprehending the groundwater recharge of a coastal city in humid tropical setting using stable isotopes.

Unscientific urbanization in coastal cities has enforced the need for understanding groundwater recharge sources and processes for sustainable development. In this paper, stable isotope compositions of precipitation, groundwater and river water were determined to understand the significant recharge sources of phreatic aquifers in the two differently urbanized environments, viz. urban and peri urban clusters of Kozhikode District, Kerala, and southern India. The two monsoon systems viz., southwest and northeast, are the major source of groundwater recharge in the region, but due to change in landuse pattern in the last decade has significantly altered groundwater recharge. Hence with the aid of stable isotope ratios of water, estimation of point recharge of rainwater to the groundwater in different hydrgeological setting of the area was done. The monsoon rains contributed 35% in the urban alluvial aquifers, up to 39% in the urban laterite aquifer and 42% in the peri urban laterite aquifer. An attempt was made to correlate the landuse changes in the past decade in the region with the groundwater availability.