Karst merupakan istilah dalam bahasaJerman yang diturunkan dari bahasa Slovenia(kras) yang berarti lahan gersang berbatu. Istilahini di negara asalnya sebenarnya tidak berkaitandengan batugamping dan proses pelarutan,namun saat ini istilah kras telah diadopsi untukistilah bentuklahan hasil proses perlarutan. Forddan Williams (1989) mendefini-sikan karst sebagaimedan dengan kondisi hidrologi yang khassebagai akibat dari batuan yang mudah larut danmempunyai porositas sekunder yang berkembangbaik.

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Karst aquifers are important water resources but highly vulnerable due to their heterogeneous and complex characteristics. Various hydrological aspects (recharge, flow behaviour) have to be known in detail to develop a sustainable concept for water collection, distribution and treatment. In the karst area of Gunung Sewu (Java, Indonesia) such a concept was to be implemented within a German-Indonesian joint IWRM project. The basic hydrogeological conditions and water quality aspects were characterized on a regional scale through hydrochemical monitoring of springs, wells, subsurface and surface rivers. More detailed information about the recharge, flow and storage behaviour was obtained from high resolution monitoring of T, EC and discharge in one large underground river system. The water quality is well below any guideline values with regard to inorganic pollutants during dry season. During rainy season, dissolved Al concentrations are frequently above the Indonesian guideline value. Slow matrix flow is the most important recharge component during dry season, thus assuring the year-round water availability in the subsurface karst. During rainy season, quick infiltration of the surface water is a dominant recharge component. Rapid response of discharge, T and EC to heavy rain suggests the presence of point recharge that feeds a highly karstfied conduit system with fast conduit flow and short transit time of water. The strong variations in discharge and hydrochemistry are particularly challenging for technical water usage and treatment facilities. Piston flow is indicated to be the third important flow component and is induced by heavy rainfall.

The Karangbolong karst is situated in the southern zone of Java where Miocene limestone has been uplifted and has experienced karstification since the late Pliocene. The research documented here aims at exploring morphological characteristic of the area. Special interest is attributed to differentiation of valley or depression morphology, conical karst morphology, and the roles of jointing system and uplift history in their development. The morphology investigation was mostly undertaken using aerial photograph visual interpretation of panchromatic aerial photograph and analytically shaded DEM, as well as field observations. The results show that the general morphological features of Karangbolong karst are characterized by aligned valleys and aligned enclosed depression with three different patterns. The orientation of the valleys and enclosed depressions coincide with the structural pattern of the area, indicating that the formation of aligned valleys and aligned enclosed depressions is preferential dissolution through jointing. The residual hills are typified by conical karst morphology with sharp peaks. It is found that tight joint spacing appears to be the main reason for the sharp peak of the conical hills. Asides from jointing system, morphology of the area is likely governed also by topographical position and gravity sliding of the limestone bed during the uplift. Uplift history has important control on the differentiation of morphology between plateau part and sloping part. Limitation of this research is that the aerial photograph was not rectified well, because the analyses in this research

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