Hydrogeological Characterization of the Gunungsewu Karst Area in the Upper Reach of Gremeng Karst Drainage Basin, IndonesiaAhmad Cahyadi, Tjahyo Nugroho Adjis, Eko Haryono and Margaretha WidyastutiE3S Web Conf., 325 (2021) 08006DOI: https://doi.org/10.1051/e3sconf/202132508006