Study On The Variation Of Sediment Load In Weihe River And Its Driving Factors

Due to climate change and human activities,runoff and sediment load showed evident changes in many rivers around the world.This study collected the annual sediment load at 15hydrological stations,climate variables at 64 meteorological stations,vegetation cover,land use,and digital elevation model in the Weihe River basin.The Mann-Kendall trend test,ordered clustering method and Pearson correlation coefficient method are used.The method of partial least squares regression is used to analyze the temporal and spatial evolution of sediment load in the basin and interval scales,to explore the changing characteristics of the driving factors of sediment load change,to extract the driving factors affecting the sediment load in the interval,and to establish the sediment load-key indicator relationship model.The main findings can be summarized as following:（1）Temporal and spatial variation of sediment load in the basinThe sediment load volume in the Weihe River Basin from 1961 to 2015 showed a significant decrease.The average sediment load volume of the main stream of the Weihe River,the Weihe River and the Beiluo River were 90,188,and 60 million t/a,respectively.The sediment load in the basin occurred twice in 1978 and 1996,and the Fengsha section and the Pingsha section were experienced.In the three periods of the dry sand section,it is now in the dry season;the amount of sediment coming from the hydrological stations in the main stream of the Weihe River,the Weihe River and the Beiluo River has decreased significantly;most of the hydrological stations’annual sediment load sequence mutations occurred in the 1970s and 1990s.In the 1970s,they entered a stable sediment load period and entered the low sediment load period in the 1990s.The sediment load in some areas of the Weihe River Basin showed a significant decrease.In most areas of the Weihe River,the amount of sand has decreased year by year,and most of the intervals have been mutated.The sediment load modulus in the upper and middle reaches of the basin is relatively large.After2000,the sediment load modulus in 12 subcatchments is less than 5000t/（km²·a）.（2）Driving factors of sediment load in river basinDuring the study period,the driving factors of sediment load changed significantly.The precipitation in the Weihe River Basin and its various areas showed a decreasing trend.The rainfall indicators in each interval showed a certain time and spatial variation.From 1981 to2015,the vegetation coverage of the Weihe River Basin increased,and the vegetation coverage of the Weihe River Basin showed a favorable trend,with the mainstream of the Weihe River.Compared with the mainstream of the Weihe River and the Jinghe River,the vegetation coverage in the Beiluohe area is better,and the area covered by high vegetation is more.The area of grassland,forest land,cultivated land in different periods in the Weihe River Basin are more than 96%.The proportion of grassland,woodland and construction area increases with time,while the cultivated land area decreases.In recent years,water conservancy and conservation projects and ecological measures,such asterraces,silt dams,forests,reservoirs,etc.The changes in sediment load has a profound impact.（3）Correlation analysis between sediment load and potential driving factors in river basinThe sediment load modulus（Sm）in the basin is affected by the driving factors such as rainfall,vegetation,topography and land use,and annual rainfall（P）,vegetation cover index（NDVI）,elevation minimum(H_min),and average slope（S）.The indicators of maximum height difference（Hd）,grassland area specific gravity（GR）,and river network density（Rd）show a good correlation,and establish a relationship model in stages:1981-1996:Sm=0.071P-0.461NDVI-0.129H_{mi n}+0.270S+0.416GR+0.076Hd（R²=0.61）1997-2015:Sm=0.190 P-0.364NDVI-0.183H_min-0.069S+0.408GR+0.425Rd（R²=0.58）...