Investigation of the State and Condition of Saltwater Intrusion in Cebu City Aquifers in the Philippines
In the Philippines, Cebu City has been declared as among the major cities with the most critical balance conditions suffering from the depletion of groundwater sources and the incidence of saltwater intrusion. Well-monitoring and plotting of isohaline contours have been conducted by the Metro Cebu Water District (MCWD). However, not much attention had been given to construct a groundwater model of Cebu City with updated data. This paper presents a simplified analytical model of the Cebu City aquifers to determine the current position of the presumed sharp saltwater-freshwater interface, as well as visualize the drawdown and upconing conditions. Ten representative wells were assessed individually regarding the likelihood of saline contamination. Moreover, the upconing of these ten wells has been simulated considering the effects of well interference. In defining the freshwater head and the distance of the toe of the freshwater-saltwater interface from the shore, the Glover relation was primarily used. Simulation results are illustrated by two- and three-dimensional representations. Calculations and graphical representations were all carried out using Microsoft Excel spreadsheets. Three of the ten wells were shown to be contaminated, while two more are threatened. Simulations with 2014 groundwater data also show an alarming drawdown condition in the aquifer. Aside from the contribution to a greater public awareness of the threat of saltwater intrusion, the findings may serve to guide the policy-making of MCWD with regard to establishing allowable rates of groundwater extraction.
Keywords - Saltwater Intrusion, Aquifer, Drawdon and Upconing Conditions