Subsurface Flow and Surface Water Interactions Quantification in Gunung Kidul Karst Area Using HydroChemical and Stable Isotopes Data Variations

Subsurface flow is one of the available water sources in the Karsts area such as in Gunung Kidul. The study of the pattern of the variations of stable isotopes content as a function of time and its interaction with other water sources such as rain waters, groundwater, river water will be a very good tool to assess the potential of the subsurface flow as a water source. For this purpose, the variations of stable isotopes content of subsurface flow around Gunung Kidul Karsts area and its interactions with other local water sources have been studied for the last two years. From the comparison of stable isotopes variations pattern of the subsurface flow with monthly rain water, the interaction of the subsurface flow with other water sources in the area has been quantified. Based on hydro-chemical data, it was found that the recharge area of subsurface flow were relatively further than other samples and it was also found that Seropan and Bribin subsurface flow systems originate from different geologic structures. Based on stable isotopes relative contents, it was found Ngobaran and Baron Caves have been
mixed with domestic sewerage water or other surface water.

Keywords : Karsts area, stable isotopes, subsurface flow