THE DISTRIBUTION OF FLOOD HYDROGRAPH RECESSION CONSTANT FOR CHARACTERIZATION OF KARST SPRING AND UNDERGROUND RIVER FLOW COMPONENTS RELEASING WITHIN GUNUNG SEWU KARST REGION

Abstract

This research is carried out within two caves with underground river and
one karst spring, which is located in Gunung Sewu karst area, Gunung Kidul. The
objective of this research is to recognize some flood hydrograph properties of karst
aquifer characterization in order to compare the comportment of aquifer to release
its flow components between underground river and karst spring. Water level data
loggers are installed within two caves and one karst spring represent upper,
middle, and lower elevation of karst topography, which are Beton, Seropan, and
Toto Cave, respectively. In addition, time series discharge measurement in
correspond to minimum, average, and maximum flow events is conducted to
formulate the Annual Stage Discharge Rating Curve. Thereby, the full year river
hydrograph may be defined. Afterwards, by selecting several flood hydrograph
events, the recession constant in each cave including diffuse flow (Kb), and fissure
flow (Ki), and conduit flow (Kc) recession constant, is then calculated and
compared in every location. The result shows that Beton Spring that represents the
upper part of research area confirms the quickest respond towards rainfall events.
Also, this point specifies the medium number of diffuse recession constant
(Kb=0.983), compared to Seropan (0.996), and Toto (0.937), means that the
aquifer surrounding Toto Cave release its groundwater storage faster than Beton
Spring and Seropan Cave. On the contrary, Seropan Cave performs the highest
value of diffuse recession constant (0.996) and this situation is confirmed by its dry
season discharge that still above 810 lt/second.