现代黄河水下三角洲的地貌特征及演化

本文主要根据黄河水利委员会多年固定断面的测量资料和海洋地质研究所1988年两个航次调查结果,结合黄河水沙资料的分析,对水下三角洲的地貌特征、地貌演化及形成机制进行了论述,尤其对三角洲前缘的地貌演化趋势进行了较详细地阐述。

GEOMORPHIC FEATURES AND EVOLUTION OFTHE SUBMERGED DELTA OF THE MODERNYELLOW RIVER

The Yellow River Delta is formed as a result of the accumulation of sediment transported by Yellow River from the Loess Plateau. This paper is based on previous studies and investigation data in 1988, to try to make clear morphological features and evolution of the submerged Yellow River Delta. The mean annual silt discharge of the Yellow River is about a billion tons and runoff about 40 billion m3. The silt and water have been greatly lessened in recent years due to the conservancy engineering. The former became 0.44 billion tons and latter 19.5 billion m3 each year during 1986-1991. Morphological features of the submerged Yellow River Delta are divided into the following types, delta front(consisting of mouth bar and distal bar), prodelta and mud bay. The mouth bar is the growing point of the Yellow River Delta. Its stability has a direct effect on stability of the river mouth and life-time of the channel. The slope of the mouth bar is very steep. In its lower part, there is a complex topography and a large unstability, facilitating the resuspension of sediments. And the strong tidal current at the front edge of the bar, can help transport the sediments. River water can push aside sea water, flow 8-10km into the sea from river mouth and form scour structure on the sea bottom during the flood period. River mouth has occasional swings, which often form erosional surface on certain sections. This is an important geological phenomenon attention should be paid to when studing depositional model of the Yellow River Delta. Data of geomorphological evolution indicate that the lateral distance of transported silt is 16-20km in width. Artificial measures must be adopted if there is a need to increase diffuse range. We have known from geomorphological studies that the advancing rate of mouth bar can directly influence the gradient of the lower river channel, therefore, mouth bar should be harnessed first before the river mouth is harnessed.