ANALYZING RUNOFF DYNAMICS THROUGH PARAMETERIZING A HYDROLOGICAL MODEL IN A WATERSHED: A CASE STUDY IN UPPER SERAYU BASIN, CENTRAL JAVA PROVINCE, INDONESIA

This research constructed a hydrological model by means of available data, hydrological equations, and GIS program to find out the runoff dynamic on the study area. The runoff dynamic was analyzed by describing runoff on different land cover types, figuring the correlation between hydrological component and runoff, calculating the sensitivities of the hydrological components to runoff, and identifying the response of runoff to possible land cover change. The model resulted that the highest runoff occurred on built up area and the lowest occurred on cultivation area. Infiltration was also the hydrological component that mostly influenced runoff. Replacing forest, shrub, and plantation by cultivation greatly reduced runoff up to 49 %. Enlarging forest area increased runoff about 12 %. Based on those findings, the hydrological component having the strongest correlation with runoff gave the most influence to runoff change, and enlarging forest area does not always decrease runoff.