Rainfall–discharge relationship and karst flow components analysis for karst aquifer characterization in Petoyan Spring, Java, Indonesia

This research was conducted at the Petoyan Spring, one of the important karst springs in the western part of Gunungsewu Karst, Java, Indonesia. The main purpose of this study was to (1) define the relationship between the rainfall pattern and the discharge of Petoyan Springs and (2) analyze the spring flow component, relating to the discharge of the rainfall response to the karst aquifer characterization. Spring discharge fluctuation and precipitation data over a 9-month period were analyzed by bivariant, cross-correlation, and factual comparison to determine the correlation between rainfall and spring discharge. The calculation of hydrograph recession constants for diffuse, fissures, and conduit flows was conducted to understand the karst aquifer properties to recharge the spring discharge. Then, the diffuse flow recession constant value was used to separate the conduit and diffuse flows of the Petoyan Spring. The results showed that the voids system in the Petoyan Spring performed a rapid discharge response to rainfall, because the conduit system is already developed. The rapid response also shown by the highest correlation between rainfall and discharge amounted to 0.281 h in time lag. The recession constant value for Petoyan Spring of each component is 0.997 (diffuse flow), 0.721 (fissure flow), and 0.449 (conduit flow). However, the percentage of monthly diffuse flow is between 79.79 and 80.26 %, which still shows the dominance of diffuse flow in the karst aquifers.