Analysis On The Water And Sediment Variation In Yellow River And Its Influence On The Change Of Yellow River Delta

The Yellow River is the second largest river in China and is also one of the world?s most sandy rivers.This situation has seriously affected the ecological environment and the production and life of the people in the Yellow River basin.Since the founding of the People's Republic of China,the party and the state had attached great importance to the treatment of the Yellow River.Due to a series of engineering construction and the influence of natural factors,the runoff and sediment discharge has been a dramatic change in recent decades,especially the amount of sediment flux lost,which has taken place a series of great changes in the Yellow River delta form and area in recent decades.This study analyzed the relationship between the change of water and sediment and the change of the Yellow River delta under the influence of the major events in the Yellow River basin in recent decades,which is based on the measured rainfall data of main weather stations in the Loess Plateau,runoff and sediment discharge data of hydrological station in the Yellow River and remote sensing data of the Yellow River delta area.The results are as follows:1.The annual runoff and sediment discharge of the main stream in the Yellow River is a significantly declining trend except for Tangnaihai hydrological station.Mann-Kendall statistics of runoff and sediment discharge at Tangnaihai hydrological station are-0.95 and-1.36 respectively,which is not reaching significance level.Mann-Kendall statistics of runoff and sediment discharge at other hydrological station are-6~-4 and-8~-5,which is reaching significance level.The change point of annual runoff and sediment discharge are concentrated in the mid-1980s and the late 1990s.2.The average annual rainfall is 422.4mm in the Loess Plateau area,which were not significant change trend.Runoff and sediment discharge significant downward trend in the Loess Plateau and the time of change point is in 1985 and 1999respectively.The effect of rainfall on the runoff and sediment discharge in the The Loess plateau was 31.1%and 14.2%.The effect of human activities on the runoff and sediment discharge in the the Loess plateau was 68.9%and 85.8%.3.There is a significant correlation between the land-forming speed of the Yellow River Estuary and sediment flux of the Yellow River.Pearson correlation analysis results showed that the correlation coefficient is 0.399(P<0.05).4.The area of the Yellow River Delta has changed from increasing to decreasing and the turning point was in 1998.The turning point is basically the same as sediment discharge turning point in the Yellow River.Under the dual influence of natural factors and human activities,the decline of the Yellow River sediment discharge has led to a gradual decline in the land-forming speed in the Yellow River Estuary.The area of the Yellow River Delta showed a general decline after 1998,and it is basically consistent with the time of sediment discharge change point in 1996 in the Yellow River.5.Coastal zone protection projects has reduced the rate of erosion in the North River Bank.In 1978,the area of the North River Bank was 482.7 km~2.By 1987,the area of the North River Bank was reduced to 325.58 km~2,with an average annual decrease of 17.46km~2.After Coastal zone protection projects,the area of North River Bank in 2016 was 222.92 km~2,with an average annual decrease of 3.54km2 from1987 to 2016.The erosion rate of North River Bank is obviously slowing down.6.A series of river improvement works and the water and sediment regulation project in the lower reaches of the Yellow River still cannot change the decreasing trend of land area in the Yellow River Delta and the trend of slowing land area growth in the Yellow River Estuary.Due to a series of soil and water conservation and ecological restoration projects in the Loess Plateau,the total amount of sediment was reduced at the source.River improvement works such as t the water and sediment regulation project in the lower reaches project can only temporarily increase the sediment flux in the Yellow River,but it cannot fundamentally change the land area decreasing trend in the Yellow River Delta and the trend of slowing land area growth in the Yellow River Estuary.Since the total amount of runoff and sediment discharge has been greatly reduced from the source in the Yellow River,the area of the Yellow River Estuary will tend to decrease in the future.