Coastal groundwater and its support to the development of Gunungsewugeopark, Java, Indonesia.

Abstract Gunungsewu is a largest Tropical karst terrain of Southeast Asia, about 800 km2 broad, and composed of around 45,000 hills of cones and domes, belongs to the territory of Central Java, Yogyakarta, and east Java provinces. This area is now developed to be a national geopark, therefore such facilities including the availability of fresh water sources must be adequate. But in the matter of fact, Gunungsewu is always subjected to water scarcity especially in every dry season. Aquifer of Gunungsewu is predominantly composed of reef limestones with conduit flow typeand underground drainage system thatdischarge their water to Indian Ocean through coastal springs. The occurrence of coastal springs are generally associated with unique hydrogeologic phenomena and beautiful landscape.Due to very rough topography, steep cliffs, and difficulty to be accessed, to explore the existence of groundwater discharge in coastal area, fractal geometry analysis is applied. From the analysis, there is a correlation between the fractal dimension value of coast shoreline and the existence of spring. Shoreline segments with fractal dimension (D) higher than 1.30 is potential to the existence of coastal spring, whereas on the segments with fractal dimension less than that, spring is absent. Baron is the biggest verified coastal spring of Gunungsewu area, with flow rate 9000 l/sec average. The physical and chemical quality of the water do not exceed the drinking water standard. This represents that the existence of coastal springs in Gunungsewu area is actually potential to support the development of geopark, as additional fresh water sources and as geosites or geo heritages. Keywords Karst topography. Unique hydrogeology. Coastal groundwater discharge. Geopar