Effects of urbanisation in a shallow coastal aquifer: An integrated GIS-based case study in Cochin, India

Abstract

Urbanisation impacts the availability and quality of renewable natural resources, particularly water resources. In coastal regions, the magnitude of urbanisation and its consequences is more prevalent. However, there are limited quantitative assessments on how urbanisation affects the groundwater system, especially the groundwater potential. Therefore, in the present study, we analysed the variability in groundwater potential zones due to the temporal changes in land use land cover (LULC) for Cochin, Kerala, India. For this, a GIS-based weighted overlay analysis method was performed with six geo-environmental factors to delineate groundwater potential zones (GWPZ). GWPZ at three different decadal time points from 1992 to 2019 was derived using the representative LULC maps. Our analysis showed a significant reduction in the high potential zone, decreasing from 75.34 % to 17.53 %. Contrastingly, the low potential zone rose from 0 to 11.8 % from 1992 to 2019. The temporal change in the spatial pattern in GWPZ named Groundwater Potential Change Index (GWPCI) was derived through pixel-level change detection. We performed a long-term (1985–2017) trend analysis on groundwater levels obtained for a network of twenty-three observation wells from the study area to validate the results. The trend analysis showed that 47 % of the wells display a statistically significant declining water level trend. Subsequently, twelve wells were selected to perform a bivariate statistical analysis between the long-term trend in water level and GWPCI. Ten wells showed a reasonable agreement to the negative change in GWPCI, while two displayed no relation to GWPCI. The study illustrates the effect of LULC change patterns in the groundwater system since significant alterations were observed on GWPZ. The systematic approach adopted in the present study can contribute to sustainable land and water resource management aimed at reducing the urbanisation impact on the groundwater system in the future.