Spatial and Temporal Flood Characterization of Pindul Karst System, Gunungkidul Regency

Pindul karst system has cave system and sinking stream recharge that cause it prone against flash flood. This research will study flood characteristics in the karst system. Water level logger was installed on karst system outlet and sinking stream of Kedungbuntung to obtain discharge data at 15 minutes interval. Rainfall data is obtained by installing automatic rain gauge on middle parts of karst system. Recording of both was done for six months (January – June). Flood characteristics was obtained by flood hydrograph and rainfall characteristics. The results indicated that Pindul karst system have faster time lag (Tlag) (1.1 and 1.7 hours) than rainfall duration (1.9 hours). Excess rainfall (Pe) is rainfall characteristic that is most influencing flood incident. Temporarily, rainfall percentage becoming surface runoff (% Pe) in outlet and Kedungbuntung were greater at end of rainy season (37% and 14%) than in early rainy season (16% and 8%). Pe percentage below 50% indicated that Pindul karst system is still good in storing groundwater. In spatial term, faster flood behavior in outlet was caused by recharge from cave system and sinking stream. Meanwhile, Kedungbuntung was recharged by aquifer with domination of diffuse fracture.