1 Impact of over-exploitation in coastal groundwater on the variations in 1 submarine groundwater discharge rate in a complex two aquifer system by 2 finite element modelling: A case study from south India 3 Sundara Pandian Rajaveni 1 , Sumadevi Nair Indu 2 , Karthikeyan Brindha 3 and Lakshmanan Elango 2 * 4 5 1 Department of Civil Engineering, Mepco Schlenk Engineering College, Sivakasi -626005, Tamil Nadu, India 6 2 Department of Geology, Anna University, Chennai – 600025, Tamil Nadu, India 7 3 Hydrogeology Group, Institute of Geological Science, Freie Universität Berlin, 12249 Berlin, Germany 8 * Corresponding author email: elango@annauniv.edu 9 10 Abstract 11 The purpose of this study is to understand the impact of coastal groundwater over-exploitation 12 on the variations in submarine groundwater discharge (SGD) flux rate and seawater exchange 13 flux across the seabed. As a case study, numerical modelling techniques were applied to a 14 complex multi-aquifer system located north of Chennai, India, which has been affected since 15 the mid-1970s by overexploitation and seawater intrusion. Because of the relatively high 16 hydraulic conductivity, the model shows a higher amount of seawater inflow in the central part 17 of the region. From 2000 to 2012, the movement of seawater has increased from 17,000 m 3 /day 18 to 24,500 m 3 /day due to groundwater overexploitation from the semi-confined aquifer. 19 However, the quantum of flux from the sea to the aquifer has been reduced from the year 2006 20 due to the termination of pumping from a well field supplying a part of the city’s water supply. 21 Model simulations show that fresh groundwater of 43,312 m 3 /day and saltwater of 43,815 22 m 3 /day will be discharged to the aquifer by the end of 2030. In addition to the prevailing 23 condition, various management scenarios were also predicted to prevent the degradation of 24 groundwater quality due to seawater intrusion. By adopting managed aquifer recharge methods, 25 saltwater intrusion (rate of 4408 m 3 /day) can be reduced and SGD (rate of 22414 m 3 /day) rate 26