The Nana Kosi watershed is an area of homogeneous bedrock, undulating terrain, and a cool temperate climate where the removal of forest cover and agricultural activities have greatly accelerated the rates of erosion. This reconnaissance study estimates the current erosion rate as 0.09 mm/yr on deforested land and 0.18 mm/yr on agricultural land. By contrast, natural erosion rates vary between 0.02 mm/yr under oak and pine mixed forest and 0.04 mm/yr under pine forest. In the month of heaviest rainfall, suspended and dissolved sediment yields are 7.25-26.0 times higher in the most disturbed agricultural land than in the forest. The geological rate of surface lowering due to channel erosion may be of the order of 0.10 mm/yr.