Large wood (LW) plays an integral role in mountain stream ecosystems, exerting a range of effects on sediment transport, stream morphology, and habitat creation. Human activities, including timber harvesting and clearing of land for agricultural and industrial development, have contributed to a marked decrease in natural sources of LW and a subsequent decrease in salmon populations, which is thought to be driven in part by decreases in juvenile salmon overwintering habitat. We quantified geomorphic and hydrologic changes in seven LW addition sites in Mill Creek, a small basin in the Oregon Coast range, to determine the effect of channel size on the amount of juvenile salmon habitat created. Volumetric change and duration of floodplain inundation increased with increasing drainage area, from 11 m3 to 81 m3 for sites inundated from 0.9 to 4.1 days per year. Tradeoffs may exist, however, between channel size and the speed and duration of restoration outcomes. Larger sites respond more quickly to LW addition, but changes in smaller sites may be more enduring due to relatively lower wood mobility at these sites. The formation of secondary channels observed in these smaller sites will also likely provide valuable juvenile salmon habitat.