Seasonal and short-term changes in the hydraulics and morphology of outwash distributaries on the southeast coast of Iceland were studied in April and July, 1973. In summer, when the meltwater discharge is normally at a maximum, high current velocities occur in the distributary mouths, prohibiting saltwater intrusions. Hourly variations in flow are caused by tidal-induced changes in the water surface slope. At low tide, the surface slope is the greatest, and the current, suspended sediment load and discharge are at a maximum. A current of 3.3 m/s and a suspended sediment concentration of 5.1 g/l were measured at low tide in July, 1973. As the tide rises, the surface slope is lowered and the discharge is reduced, causing meltwater to become dammed behind a barrier spit system that forms the seaward boundary of the sandur. The distributaries migrate frequently due to fluctuations in the meltwater discharge. During periods of low discharge, wave power dominates over stream power and the distributaries are deflected in the direction of net longshore transport. Stream power increases with higher meltwater discharge, causing the distributaries to erode a more direct course through the barriers.