1996 Volume 48 Issue Special Pages 37-45
Direct runoff characteristics in several streams on the southwest slope of Mt. Merapi were identi fied, and the effects of catchment factors on the direct runoff characteristics were discussed distin guishing surface runoff and subsurface runoff. Stream flow data was taken from 6 observation points on 4 rivers. Direct runoff was separated from total runoff in each storm hydrograph. An exponential relationship was shown between rainfall and direct runoff for each storm event. There was a great amount of surface runoff just after the 1984 pyroclastic flows. Subsequently it de creased gradually because of restoration of infiltration capacity on the mountain slope. Currently direct runoff is thought to consist of surface runoff which rises in rice fields and channels, and sub surface runoff which rises in shallow groundwater. The amount of surface runoff in relation to rainfall could be estimated by the percentage area of total rice fields and channels based on certain assumptions. Subsurface runoff estimated from surface runoff could be accounted for by estimated shallow groundwater movement from 400m to 600m above sea level.
