Baseflow separation of some springs in the Jonggrangan karst area, Java, Indonesia

Abstract

Karst aquifer flow can be divided into diffuse, fissure, and conduit. Diffuse (base) flow plays a role in maintaining the continuity of karst springs. This research was conducted in the Kiskendo underground river, Mudal spring, and Anjani underground river, which is located in the Jonggrangan karst area, to determine variations in the base flow proportion in the three locations. Water level and discharge data are collected for a year (March 2018-March 2019). The water level and discharge data pairs are then used to create a rating curve to obtain flow hydrographs during the study period. Several flood events are then chosen to calculate the baseflow recession constant. Separation of base flow is automatically carried out to determine the percentage of base flow during the study period. The results showed that all three locations had fluctuating hydrographs that followed the seasons, with many peaks of flood hydrographs occurred following rainfall events. This condition shows that all three locations have developed aquifers. Although this is the case, flows in the three locations tend to be dominated by base flow both during the dry and rainy seasons, which indicates the capacity of aquifers to store groundwater is still good. Besides, the results of the base flow separation show that the percentage increases during the dry season and decreases during the rainy season. The decrease in the percentage of base flow during the rainy season is due to the contribution of direct flow (fissure and conduit) to the karstic aquifer.