CHARACTERIZATION OF THE SPATIAL AND TEMPORAL VARIATIONS OF SUBMARINE GROUNDWATER DISCHARGE IN A MICRO-TIDAL COAST OF BAY OF BENGAL, INDIA USING SEEPAGE METER MEASUREMENTS

Groundwater discharges to sea (SGD) from coastal aquifers are considered as potential pathways of solute transport and anthropogenic contaminants and nutrient flux to ocean. To quantify the spatio-temporal nature of SGD and volume in a micro-tidal coast of the Bay of Bengal in India, we have done a seepage meter study in the pre-monsoon and post-monsoon season of 2014-2015 for a full scale lunar tidal cycle, using densely gridded seepage meter experiment. One hundred and twenty seepage meters were installed in the inter-tidal zone, within an area with dimension of 60 m × 110 m. The volume of the discharged groundwater was measured and sampled from the high tide line (HTL), moving towards sea, including time variant monitoring. The measured daily average rate of discharged groundwater ranges from negligible discharge to 0.96 Lhr^-1cm^-2 during pre-monsoon season and 0.01 to 1.55 Lhr^-1cm^-2 during post-monsoon season.The highest discharge rate was observed in the second day of every tidal cycle of both seasons at a distance of 5 m offshore from the HTL. Diurnal seepage variations have been observed for the whole of study periods, which may be due to the effect of tidal height, wave set up leading to tidal loading and pumping. Similarily, the negligible discharge in the mid-shore to far-shore area reflects the tidal influence to SGD. To characterize the terrestrial SGD (T-SGD) and marine component of SGD (M-SGD) driven by SGD, mass balance study was performed. It is observed that the T-SGD/M-SGD ratio is highest in the area between 5m to 20m offshore from HTL, where the SGD rate was found to be maximum. This indicates that the local geology and tidal set up are controlling the large freshwater discharge at this site. Hence, by quantifying the effects of tide and local geology we can develop a better estimate of freshwater and nutrient fluxes at the study site adjoin the Bay of Bengal and other places with similar set-up.