Investigation of direct runoff in the intensive farming system of upstream Merawu watershed, Indonesia

Abstract

Merawu watershed is located at Banjarnegara district and categorized as degraded watershed in the Serayu river basin. Upstream area in the Merawu watershed is a mountainous area of 1,500 m a.s.l., with steep slopes and high rainfall intensity. Upstream Merawu has an important function as recharge area, protect the downstream and water supply for the Merica reservoir. Forest conversion to intensive farming practices have produced large portion of erosion, surface runoff and water pollutant. Understanding the surface runoff changes in the forest conversion to intensive farming practices is important. Investigations of direct runoff in the intensive farming system in upstream area of Merawu watershed were observed using two small catchment experiments. Catchment for intensive farming system was compared to non-disturbed catchment of Pine forest. Surface disturbances associated with soil tillage, fertilization, pesticides and mulching during 2-3 months of planting reduced the soil capacity to control rainfall. During 1-year investigation, total direct runoff (DRO) in intensive farming catchment was 360.05 mm or 34.4% of rainfall or 1.63 times higher than that in the Pine forest catchment. Unit hydrograph analysis found the direct runoff coefficient was 9.4% or 1.7 times higher than that in the Pine forest catchment. This study found the important function of canopy interception, forest floor interception, soil management and infiltration to control the direct runoff in the catchment.