The Yellow River delta is dynamic because the river carries a heavy sediment load and serious siltation occurs in the area. Massive sediment transport brings fertile soil to the river mouth leading to its expansion by 20Β±25 km 2 per year. The dramatic reduction in runoff and sediment in the delta due to increasing water demand has extended the period of flow cutoff. The river changes its delta channel about once every ten years. The channel shifts affect the upstream flood stages. Since the river shifted to the present delta channel in 1976, the shape of the delta has changed remarkably. Sediment-laden flow has been building channels by depositing sediment in low velocity areas, and has extended the river mouth into the sea for more than 40 km. The velocity of sea currents is enhanced by the growth of the river mouth spit at a rate of 1 m s Γ1 per 10-km extension, which results in high capacity of sea currents carrying sediment away from the mouth. The new river mouth area was silted up by 14 m and the old river mouth area was eroded by 5 m. Siltation takes place in the low flow season and scouring occurs in the flood season; scouring occurs during the rising limb of a flood and siltation occurs during the receding limb of a flood. The roughness of the river changes largely following the increase in discharge. The minimum Manning roughness occurs at non-siltation and non-erosion discharge. Tidal influence in the river is restricted to a section extending over only a few kilometres. Unlike in many other coastal areas, the river water with its high sediment concentration develops into density current and flows underneath the seawater during flood. This mechanism contributes to sediment transportation in the delta.