The Impacts Of Rainfall And Landuse On Runoff And Sediment Change In Dali River Basin

In recent years,due to the severe climate change and the impact of human activities,the temporal and spatial distribution characteristics of runoff and sediments in the basin have undergone tremendous changes.The Dali River Basin is an important tributary of the Wuding River.In recent years,the runoff and sediment changes in the basin have been severe.Analyzing the impact of rainfall and land use on runoff and sediment change in different time scales in Dali River Basin,which provides scientific basis for rational allocation of water and sediment resources,soil erosion control and land use planning in the basin.Based on this,the rainfall,flood and sediment data measured in Dali River Basin,land use data and basin DEM data are used to quantitatively assess the influence of rainfall and land use change on runoff and sediment change at the annual and sub-flood scales on the basis of analysis of annual rainfall,runoff and sediment change trend,identification of catastrophe points and analysis of quantitative change,transfer speed and transfer type change of land use types in Dali River Basin.The main research contents and achievements are as follows:(1)The temporal and spatial variations of rainfall,runoff,and sediment in Dali River Basin were systematically analyzed.Based on the measured rainfall,runoff,and sediment data in the study area,the rainfall,runoff and sediment transport in the Dali River Basin were analyzed by linear regression,Mann-Kendall trend catastrophe test,anomalous cumulative curve method and wavelet analysis.The results showed that the annual rainfall change trend was not significant,and the annual runoff and sediment transport decreased significantly,with the catastrophic year 1971.The main periods of annual rainfall,annual runoff and annual sediment transport are 17 a,13a and 18 a,respectively.The average rainfall in the flood season for many years is generally low in the central part and high in the East and west.Compared with 1980-1990,the average annual rainfall and rainfall duration in 2006-2015 increased,while the peak discharge,runoff depth,sediment transport and sediment concentration decreased.From 1980 to 1990,the spatial distribution of sub-average rainfall in the basin was high in the East and low in the west.From 2006 to 2015,the distribution of sub-average rainfall in the basin was more in the middle and less in the East and west.(2)The land use evolution of Dali River Basin was analyzed.Based on the land use data of five periods in the study area,the quantitative change,transfer speed and transfer type of land use were analyzed to understand the process and characteristics of land use change in the study area in recent years.The results showed that the main land use change in Dali River Basin from 1990 to 2010 was the reduction of cultivated land and grassland,which mainly transformed into forest land.On the whole,the area of forest land changed greatly.(3)The HEC-HMS hydrological model of Dali River Basin was constructed.Based on the observed rainfall and flood data,land use and soil data,the HEC-HMS model was used to simulate the flood in different land use periods in Dali River Basin,and the rationality of the model parameters was calibrated and verified.The results show that the prediction accuracy of the two periods is grade B,and the HEC-HMS model is suitable for the Dali River Basin.(4)The impacts of rainfall and human activities on runoff and sediment change on an annual scale were quantitatively assessed.The base period and the change period are delineated by the catastrophe year.The double cumulative curve method is used to quantitatively evaluate the contribution rate of rainfall and human activities to the change of annual runoff and annual sediment transport.The results show that the human activities have an increasing influence on the runoff and sediment change in the Dali River Basin.Compared with rainfall,the impact of human activities on the reduction of runoff and sediment in the basin change period is dominant.(5)The effects of rainfall and land use on runoff change at sub-scale were quantitatively assessed.Based on the HEC-HMS model of Dali River Basin,the effects of rainfall and land use on runoff change in different scenarios on field scale were analyzed.The results showed that during 1980-2015,the increase of average rainfall and the decrease of cultivated land,grassland and woodland caused the decrease of peak discharge and runoff depth by 30.85% and 18.49% respectively.(6)The effects of rainfall and land use on sediment change at field scale were quantitatively assessed.Based on the land use data and measured rainfall and sediment data of Dali River Basin,the sediment change and its contribution to sediment change under different rainfall and land use scenarios were quantitatively assessed by using multivariate linear statistical model analysis method.The results showed that during 1980-2015,the sediment transport and sediment concentration decreased by 50.98% and 42.56% on average due to the combined changes of the average precipitation of field floods and the decrease of cultivated land,grassland and woodland.