Rainfall-runoff Investigation of Pine Forest Plantation in the Upstream Area of Gajah Mungkur Reservoir

Vegetation cover change has a profound influence on the hydrological cycle. A reduction in vegetative cover from forest harvesting generally increases the average surface runoff volume and total water yield for a given area of land. The differences of structure and land cover type are the main baseline in this research to understand the hydrological response of catchment. This research is using two catchment experiments, pine forest and mix-plant forest catchments. Plantation forest with clear cutting system in the mountain area is very sensitive with the changes of runoff and soil erosion. This study investigated the impact of vegetation changes on rainfall-runoff response in different type and periods of Pine forest plantation from their respective forestry treatments. The result shown that in the 7-year old mix-plant forest, direct runoff, peak discharge and runoff coefficient are dramatically increased than that in the 37-year old pine forest. 15 years after planting, direct runoff, peak discharge and runoff coefficient are decreased and reaching to the 37-year old pine forest responses. Implementation of a mix-plant forest method is effective in controlling the hydrological responses of direct runoff, peak discharge and runoff coefficient. The results showed that the magnitude of runoff during different forest treatments depend on interactions among rainfall, forest cover changes and surface disturbance. Forest management practices should consider and attempt to minimize disturbance during each plantation stage to control runoff response.