黄河三角洲发育是河口区河流动力及陆域物质通量与海洋动力及海域物质通量相互作用的产物 ,三角洲造陆速率取决于上述两方面的对比关系。当上述两方面处于平衡时 ,三角洲造陆处于临界状态 ,即净造陆速率为零 ,与之相联系的入海泥沙量和径流量可视为黄河三角洲造陆过程的临界水沙条件。运用经验统计方法估算出 :当入海年沙量Qs为 2 78亿t/a、入海年水量Qw为 76 7亿m3时 ,或者当关系式 3 1934Qs+ 0 0 85 6Qw=17 94得到满足时 ,黄河三角洲造陆过程处于临界平衡状态。在黄河流域的环境管理中 ,应将上述两项临界值作为约束条件。黄河流域生态用水量的内涵应予以扩展 ,维持三角洲造陆平衡所必须的入海径流量 ,应作为黄河流域的生态用水量。

The Yellow River is the most famous heavily sediment laden river of the world, its land accretion process is sensitive to influencing factors such as the changing precipitation and human activities. Thus, the Yellow River Delta provides an ideal site to study the delta development under the land ocean interactions. The development of Yellow River Delta can be regarded as the outcome of interactions between the river and marine dynamics and of interactions between the river and tide transported material fluxes. The rate of land accretion is controlled by these interactions. When the above two aspects are in equilibrium, the land accretion process of delta may be thought under the critical conditions, and the river supplied water and sediment quantities may be considered as thresholds of runoff and sediment for land accretion. By comparison between the sea charts and remotely sensed images made in different periods, the annual area of land accretion has been obtained. To identify the water and sediment thresholds for delta development, two regression equations have been established between land accretion rate and water and sediment quantities into the river mouth, based on the data from the Yellow River Delta in the period of 1955 1989. From these relationships, the threshold of river supplied sediment quantity for land accretion has been estimated as 2.78 10 8 t, and the threshold of runoff as 76.7 10 8 m 3 ; under these sediment and water supplies, the Yellow River Delta may be in equilibrium in an average sense. In other words, if the annual sediment quantity is less than 2.78 10 8 t, and the annual runoff less than 76.7 10 8 m 3 , the delta might be eroded and the land would be lost, and thus the environmental security of the delta might be seriously affected. For a better management of the environment of the Yellow River, these thresholds should be taken as one of the constraints. The meaning of ecologically needed water use in the Yellow River should be extended, in order to include the water quantity that is required for maintaining the balance of land accretion in the delta.