Impact of forest land cover on runoff, erosion and sedimentation in the Karai Watershed, Simalungun Regency, North Sumatra Province, Indonesia

Abstract

Development activities in the  Karai Watershed, in upstream area, are intensive. The activities tend to decrease the land abilities in absorbing water and protecting surface soil for erosion, which finally affect the rise of   vegetation  damage,  soil damage,  surface run-off and erosion The method of taking samples and analyzing environmental damage were conducted by purposive sampling. Data from laboratory tests of soil physical, chemical and biological properties were analyzed by statistical tests. Measurement result shows that the wide of Karai Watershed is 462 km², in which covered forest wide is 115.5 km² (25%) and the wide of non-forest area (garden, dwelling site, road etc) is 346.5 km² (75%). Land Cover for non forest area is the biggest sediment source in Karai Watershed. Based on observation on field and laboratory analysis, it shows that conservation activities in natural forest to garden, road, and dwelling site have caused damages to soil (parameter bulk density and total fungi) and environment with indicators of erosion, sediment materials in Karai River and Karai 7 Project location. Observation result shows that program to reduce erosion and sedimentation could be implemented by integrated management program of Karai Watershed with priorities to develop mixed garden and agroforestry.