ABTRACT: Sediment data were analyzed to determine grain-size dependant factors affecting sediment transport in a low-ordered, ephemeral watershed. Sediment and fl ow samples were collected during 22 fl ow events at the outlet of a 4·53 ha sub-watershed within the Walnut Gulch Experimental Watershed in south-eastern Arizona. Measured concentrations ranged from 4191 to 115 045 mg l −1 and included grain sizes up to 8·0 mm in diameter. Two grain-size dependent transport patterns were observed, that of the fi ner grain-size fraction (approximately < 0·25 mm) and that of a coarser grain-size fraction (approximately ≥ 0·25 mm). The concentration of the fi ne fraction decreased with fl ow duration, peaking near the beginning of a fl ow event and declining thereafter. The concentration of the fi ne fraction showed slight trends with season and recovery period. The concentration of the coarse fraction displayed a slight negative trend with instantaneous discharge and was not correlated with event duration. These patterns typically produced a condition where the majority of the fi ne fraction of the sediment yield was evacuated out of the watershed before the hydrograph peak while the majority of the coarser sediment was evacuated during the falling limb of the hydrograph. Each grain-size dependent transport pattern was likely infl uenced by the source of the associated sediment. At the fl ow event time scale, the fi nes were primarily wash load, supplied from the hillslopes and the coarser grains were entrained from the channel bed. Because transport patterns differ based on grain size, attempts to defi ne the total sediment concentration and sediment yield by the behavior of a single grain-size fraction may lead to erroneous results, especially when a large range of sediment grain sizes are present.