A relation for estimating changes in the condition of riparian vegetation as a function of stream power was developed for stream channels in central Arizona. Flood and vegetation data were collected from 13 flows at 11 sites. Stream power was computed at cross sections and plotted against the average height of vegetation for each flow. The effect of the flow - no effect, little effect, laid over, or removed - on the riparian vegetation is related to stream power and vegetation height. As vegetation height increases, the magnitude of stream power needed to affect the vegetation also increases. Stream power of about 72 Newton-meters per second per meter squared is needed to lay over 1-meter-high vegetation, and stream power of about 580 Newton-meters per second per meter squared is needed to lay over 5.5-meter-high vegetation. This relation can be used to estimate vegetation conditions at the time of peak floodflow.