Dynamic characteristics of the Yellow River mouth

The Yellow River delta is dynamic because the river carries a heavy sedimen t load and serious siltation occurs in the area. Massive sediment transport brings fertile soil to the river mouth leading to its expansion by 20-25 k m(2) per year. The dramatic reduction in runoff and sediment in the delta d ue to increasing water demand has extended the period of flow cutoff. The r iver changes its delta channel about once every ten years. The channel shif ts affect the upstream flood stages. Since the river shifted to the present delta channel in 1976, the shape of the delta has changed remarkably. Sedi ment-laden flow has been building channels by depositing sediment in low ve locity areas, and has extended the river mouth into the sea for more than 4 0 km. The velocity of sea currents is enhanced by the growth of the river m outh spit at a rate of 1 m s(-1) per 10-km extension, which results in high capacity of sea currents carrying sediment away from the mouth. The new ri ver mouth area was silted up by 14 m and the old river mouth area was erode d 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 Mann ing roughness occurs at non-siltation and non-erosion discharge. Tidal infl uence in the river is restricted to a section extending over only a few kil ometres. Unlike in many other coastal areas, the river water with its high sediment concentration develops into density current and flows underneath t he seawater during flood. This mechanism contributes to sediment transporta tion in the delta. Copyright (C) 2000 John Wiley & Sons, Ltd.