The sediment output processes for natural rainfall events monitored in three purple soil small watersheds with different
catchment areas,physical characteristics and types of land are used to investigate the sediment behaviors and their spatial dependence.The results show that the variation process of sediment concentration exhibits in three types: waveform,power-
decreasing and parabola-compounded.After the peak runoff rate,sediment concentration decreases and variation amplitude reduces.The sediment flow output is significantly affected by the spatial scale and type of storm.The erosion of even-distributed type rainfall results in waveform hydrograph of sediment flow with low concentration and increases with the area of
watershed.Whereas,following the increase of watershed area,under the action of intermittent-type rainfall the sediment hydrograph transits from parabola-compounded type into power-decreasing type.The sediment hydrograph under the erosion of mid and deluge rainfall exhibits power-decreasing type and no significant spatial dependence is found.