Simulation Study On The Characteristics Of Water And Sediment Change In Dali River Basin

The Loess Plateau is one of the most severely polluted areas in the world and the most vulnerable to ecological environment.Since the 1970s,China has carried out extensive soil erosion control measures and ecological engineering construction in the middle reaches of the Yellow River.These measures have made the basin under the pad.The surface has undergone great changes.A large number of research results show that the runoff and sediment in the Yellow River Basin show a significant decreasing trend.The general study believes that the combination of climate change and human activities makes the water and sediment change in the basin.This paper selects the Dali River Basin as a study.The object firstly judges the contribution of precipitation change and human activities to runoff and sediment,analyzes the annual and interannual variation characteristics of water and sediment at the river basin exit station(Jude Station),and then uses the semi-distributed semi-set hydrological model SWAT in the Dali River Basin.A model that meets the actual situation of the river basin is established to quantitatively analyze the causes of water and sediment changes in the basin.The analysis mainly includes different rainfall scenarios,different land use scenarios,and changes in water and sediment under silt dam scenarios.The main findings are as follows:(1)Through the analysis of hydrological factors in the basin,it can be seen that the distribution of rainfall,runoff and sediment transport in the basin is extremely uneven during the year,mainly concentrated in June-September,and the annual runoff and sediment transport volume show a significant decrease trend,and Significantly passed the 0.01 test,and the rainfall showed an increasing trend,but the change was not significant.The runoff and sediment transport of the Suide station(export station)were abruptly changed from 1971 to 1972;when the contribution was calculated using the double cumulative curve method It is concluded that the contribution of rainfall change to runoff and sediment loss is 23.21%and 7.14%,respectively.The contribution of human activities to runoff and sediment loss is 76.79%and 92.86%,respectively.The main reason for the significant decrease in runoff and sediment transport in the Dali River Basin from 1960 to 2015.(2)Taking the actual situation of the Dali River Basin as a reference,using the existing measured data and digital data of the basin to construct a database that can truly reflect the actual situation of the Dali River Basin,and the rate of 1991-1993 as a model is regular,1994~2000 As the verification period of the model,the semi-distributed semi-set total SWAT hydrological model was used to operate in the Dali River Basin.The model was validated and verified by SWAT-CUP.It is concluded that the decision coefficient R2 and the Nash coeff-icient NS of the periodic flow rate(1991-1993)are 0.73 and 0.70,respectively,and the R2 and NS of the sediment transport are 0.80 and 0.64,respectively.(1994-2000)R2 and NS of runoff are 0.84 and 0.82,respectively,and R2 and NS of sediment transport are 0.83 and 0.82 respectively.The NS and R2 in this simulation output can meet the accuracy requirements of the model,so SWAT is used.The model derives the water and sediment values of the Dali River basin on the space-time scale,which can be applied to the actual analysis process.(3)Using the SWAT model to divide the Dali river basin into 91 sub-basins,and the output of 91 sub-basins from 1991 to 2000(10 years)as the basic data,analyze the spatial and temporal distribution of rainfall,evaporation and surface runoff from 1991-2000.Analyze the convergence process of runoff,sediment transport and runoff erosion power in the basin,as well as the spatial and temporal distribution of runoff modulus,sediment transport modulus and runoff erosion power over the entire basin.The study shows the average annual rainfall from 1991 to 2000.The amount is mainly concentrated in the southeast and west of the basin.The evapotranspiration is also concentrated in the southeast and west of the Dali River Basin.The surface runoff of the basin is mainly concentrated in the lower reaches of the basin.The runoff modulus,sediment transport modulus,and runoff erosion power are upstream.As the whole downstream increases,the runoff modulus and sediment transport modulus of the tributary are smaller than the dry flow,but the runoff erosion power of the tributary is greater than the dry flow.(4)Quantitative analysis of the causes of water and sediment changes in the Dali River Basin,using the functions of the SWAT model to simulate the situation,analyze the impact of precipitation and ecological construction on runoff and sediment transport in the basin,and analyze that:daily rainfall increases 10%,the flow rate and sediment transport increased by 26.72%and 25.39%respectively,and the daily rainfall decreased by 10%,the flow and sediment transport decreased by 23.28%and 21.77%respectively;15° and above were both forest and grassland.The water and sediment values will all reduce sand.When the whole basin is cultivated,the water and sediment at the exit of the basin will increase.When the basin is all forests and grasslands,the water and sediment at the exit of the basin will be reduced.The effect of reducing water and sediment in the forest is greater than that of the grassland.The effect of reducing water and reducing sand,the presence of silt dam will reduce the flow and sediment transport,and the effect of reducing sand is better than the effect of reducing water.