An Isotopic Approach to Investigate Seepage in Dam: Case Study Ciawi and Sukamahi Dry Dams, West Java, Indonesia

Seepage control in the dam is vital in maintaining dam safety. It is important to determine the source of seepage water to be controlled so that there is no excessive seepage that threatens dam stability. This study used Physico-chemical parameters and stable isotopes (δ²H and δ¹⁸O) to determine groundwater characteristics, the groundwater origin around the dam, and the connectivity of the Ciawi and Sukamahi Dry Dam’s seepage with surrounding water sources. This research shows that the groundwater in the study area includes freshwater with TDS values varying from 62 ppm to 189 ppm and EC values from 62 μS/cm to 414 μS/cm. The results of stable isotope analysis showed that the composition of seepage and groundwater sources around the dams are around the local meteoric water line (LMWL); this indicates that groundwater is more influenced by rainwater. Comparing the composition of δ²H and δ¹⁸O showed that the seepage water from the two dams has the same genesis as springs in Sukakarya Village (MA02) and dug wells in Gadog Village (SG13). This information is beneficial in determining the handling of seepage in the Ciawi dan Sukamahi Dry Dams.