Numerical simulation of electric conductivity fluctuations due to groundwater pumping in a coastal aquifer

The Motooka area of Fukuoka prefecture of Japan is an agricultural area located on a coastal aquifer where the groundwater is being exploited for drinking and green house agriculture. The groundwater is the main water supply for drinking and greenhouse agriculture. With the increased water demand, groundwater is being extracted at the rate of 1,200m³/day. The salinity of the pumped water has been analyzed periodically and it has found that the aquifer is affected by the saltwater intrusion due to over exploitation of groundwater. The high salinity of pumped water is not suitable for both drinking and greenhouse farming. The salinity fluctuation in the pumped groundwater has become an important issue to attract much attention of the green house farmers due to its significant effect on their crops. To the authors' knowledge, research on the salinity fluctuations with groundwater pumping and their effects on seasonal recharge of groundwater in the Motooka region has not been conducted thus far. In the field of numerical modeling of saltwater intrusion, so far the simulation of salinity fluctuations is not significant. Therefore authors found a keen interest on numerical simulation of the saltwater intrusion and the salinity fluctuation phenomenon in the Motooka. To this end, a three dimensional density dependent finite difference solute transport numerical model was developed. Due to the distributed nature of pumping well locations and non-uniform geological conditions; a three-dimensional model was needed to understand the saltwater intrusion and salinity fluctuations in the Motooka. The developed model is capable of simulating the saltwater intrusion and the salinity fluctuations due to groundwater pumping for satisfactory extent.