Study On The Trend Of Water And Sediment And The Model Of Sediment Transport In Typical Drainage Area Of Three Gorges Reservoir Area

The Three Gorges reservoir area is a major prevention and control area for soil erosion in China and belongs to one of the four major water and soil loss areas in the upper reaches of the Yangtze River.For many years,the sediment problem has always been one of the focus issues of the society.It is important to find out the sediment volume of the Three Gorges reservoir and forecast it.This is an important research direction to effectively solve the sediment problem in the reservoir area.The paper focused on the rainfall,runoff,and sediment transport hydrological sequences in the three typical drainage basins of Long River,Xiangxi River,and Modao Creek in the Three Gorges Reservoir Area from 1960 to 2010,and carried out the following research: analyzed the rainfall in three typical drainage basins.Runoff and sediment transport trends,abrupt changes,and seasonal variations.The linear regression,the Theil-Sen's slope estimation,the Mann-Kendall non-parametric statistical test,and the five-year sliding average method were used to analyze the trend of water and sediment changes.The Mann-Kendall mutation point detection method and the sliding t test method were used for the mutation analysis.The analysis of sexual characteristics uses wavelet analysis.At the same time,a double cumulative curve method was used to quantitatively study the contribution of human activities to the runoff and sediment transport in the river basin.Based on the analysis of the main influencing factors affecting sediment delivery in the basin,a multi-regression model for storm sediment transport was established.The main conclusions are as follows:(1)In the past 50 years,the precipitation,runoff,and sediment transport in Longhe,Xiangxi,and Modao Creek have all decreased,but the reduction in sediment transport has been the most significant.(2)The Mann-Kendall test and sliding t test were used to analyze the abrupt changes in rainfall and runoff in recent years in the Longhe,Xiangxi,and Modaoxi basins.The results show that during the period from 1960 to 2010,the rainfall abrupt change occurred in the Long River Basin in 1999,and the abrupt change in the runoff occurred in 2004.There was no obvious abrupt change in the sediment discharge;the abrupt changes in the rainfall and runoff in the Xiangxi River Basin In 1991 and 1985,there were two abrupt changes in the amount of sediment transported,in 1990 and 2000.The abrupt changes in rainfall in the Long River Basin and Xiangxi River Basin did not result in abrupt changes in runoff.The abrupt changes in rainfall and runoff in the Modaoxi River Basin occurred in 2005 and 2004,respectively,and the abrupt changes in rainfall and runoff were basically the same.Sudden changes in sediment transport occurred in 1995.(3)The wavelet analysis method was used to analyze the periodic characteristics of rainfall,runoff and sediment transport in the Longhe,Xiangxi and Modaoxi river basins.The results show that for the same catchment,the main periods of rainfall,runoff,and sediment transport in the catchment are generally the same,and there are 12 to 13 years,6 to 7 years,and 2 years of main periods for the flow and sediment changes in the Longhe River Basin;Xiangxi River There are main periods of 10 years,6 to 8 years,and 2 years in the water and sediment changes in the basin.There are 11 to 13 years,5 to 7 years,and 2 years of main cycles in the Modao Creek basin.The changes of water and sand under the significant cycles of the three watersheds indicate that the rainfall,runoff,and sediment transport have a good correlation in the significant cycle,and the change of the runoff in the watershed depends almost entirely on the change in rainfall.Affected by changes in rainfall,it is also affected by human activities.(4)Using the double-accumulation curve method,the contribution rates of human activities to runoff changes and sediment transport changes in the river basins in the Longhe,Xiangxi,and Modaoxi basins were analyzed.It is revealed that the contribution of human activities to the reduction of sediment discharge in river basins increases with time,while the contribution rate to the changes of runoff in the basin is not significant.(5)A mathematical relationship was established between the annual precipitation in the catchment and the annual rainfall in the flood season,and the annual sediment yield in the catchment was calculated using the annual runoff in the catchment and the runoff during the flood season.The results showed that the correlation coefficient passed the significance of 0.01.The horizontal test,but the use of watershed runoff to estimate the amount of sediment in the river basin is better than the result of using the rainfall to estimate the amount of sediment in the river basin.A multi-regression model was established for estimating the amount of sediment in a river basin using the sub-basin rainfall,sub-peak modulus,and secondary runoff depth.The actual measured values were compared with the calculated values.The results show that the model can predict the basin sub-stream losses better.The amount of sand,and the accuracy is higher than the runoff erosion power model.