Determination of Recharge from Stable Isotope Data to the Hydrological Systems in the Southern Negros Geothermal Field and its Environs, Philippines

Abstract

The Philippine Meteoric Water Line equation of 2H = 8 18O + 12 is defined from the isotopic composition of rainfall in various geothermal areas of the Philippines. This equation suggests that recharge to the shallow and deeper groundwater systems in the Southern Negros Geothermal Field originates from precipitation at elevations that are about 250 meters lower than the recharge to the deep geothermal system. Rainwater in the rainy months of July to October effectively contribute to recharge, while rainwater in the dry months, although of significant amount, do not recharge the groundwater systems but run off to the surface water bodies.
The identification of such areas promotes better management and protection of the recharge areas and guides reforestation programmes for watersheds.