The Variation Of Runoff And Sediment Load In The Beiluo River Basin And The Driving Factors

The water and sediment situation in the Beiluo River Basin has changed significantly in recent decades,resulting in a series of new problems in Beiluo River Basinthe regional water resources management.It is of great significance to explore the changing rule and driving factors of water and sediment in the Beiluo River Basin for the planning and ecological environment construction of Beiluo River Basin.In this study,Beiluo River Basin was taken as the research area,and the hydrometeorological data and land use remote sensing data of the main tributaries in the Beiluo River basin Basin were collected and sorted out.Through Mann-Kendall trend test,Mann-Kendall mutation test,anomaly accumulation method,wavelet analysis and other methods,the temporal and spatial distribution of runoff and sediment transport and their driving factors in Beiluo River Basin was analyzed,the characteristics and driving factors of water and sediment changes were discussed,and the The contribution of climate change and human activities to water and sediment changes in Beiluo River Basin was quantitatively calculated by the double mass curves and hydrological sensitivity analysis.The main conclusions are as follows:(1)From 1937 to 2018,the runoff and sediment loads of the Beiluo River Basin showed a significant decreasing trend and had obvious periodic changes.The average annual runoff of the Beiluo River Basin from 1937 to 2018 was 7.48×10~8 m~3,and the average annual sediment load from 1956 to 2018 was 0.61×10~8 t.Runoff and sediment transport showed a significant decreasing trend(p=0.01),with abrupt changes of 1994and 1999,respectively,showing obvious cyclical changes of abundance-flatness-dryness.The average annual runoff in the abrupt change period was 5.88×10~8m~3,which decreased by 27.76%compared with the reference period.The average annual sediment load in the change period was 1.20×108 t,which decreased by 85.43%than that in the reference period.The annual average runoff has periodic changes of 5a,14a,34a and 54a scales,and the periodic changes of 54a scale occupied the main period.(2)The characteristics of incoming water and sediment in different hydrological intervals in the Beiluo River basin were obviously different.The sources of water and sediment into the intervals were come from different regions.Most of the water and sediment inflow in hydrological regionalization mainly concentrated around 1970 and suddenly changed around 2000,and the water and sediment inflow in the upper reaches had obvious characteristics of abundant,flat and dry stages.The loess hilly and gully area in the upper reaches of the Beiluo River was the main sediment-producing area,and the loess hilly forest area in the lower reaches was the main water-producing area.(3)The main driving factors that affecting the change of water and sediment in the Beiluo River Basin are were precipitation,air temperature,land use,and soil and water conservation measures,etc.There was no obvious change trend of precipitation in the Beiluo River Basin over the study period.The average annual temperature showed a significant increasing trend(p=0.01),and suddenly changed in 1986.From 1990 to 2015,the area of woodland and construction land in the basin continued to increase,while the area of cultivated land and water continued to decrease.The area of grassland fluctuated.Grassland,cultivated land and woodland were the main land use types of the basin.From1970 to 2006,the area of soil and water conservation measures in the Beiluo River Basin increased from 125 km~2 to 8201 km~2,with an average annual water runoff reduction of265×10~8m~3 and an average annual sediment reduction of 14×10~8 t.(4)Human activities were the main driving factors of water and sediment reduction in the Beiluo River Basin.For the runoff and sediment reduction,the contribution rate of human activities accounted for more than 90%.In the two change periods(1971-1994and 1995-2018,respectively)calculated by double mass curves,while it was 90.98%calculated by the water balance equations.For sediment reduction,human activities contributed 100.4%.