| The Malian River Basin is located in the soil erosion area of the Loess Plateau in the middle and upper reaches of the Yellow River.Studying the changes in water and sediment in this basin is of great significance for the ecological environment protection of the Yellow River Basin.This article takes the Malian River Basin as the research area and simulates the impact of the"Gully Consolidation and Highland Protect"（GCHP）project on runoff and sediment based on the SWAT model.Based on this,the CMIP6 climate model is used to set up future climate change scenarios,predict the future hydrological response of the basin,and explore the trend of future water and sediment changes in the GCHP project area.The main conclusions are as follows:（1）From 1961 to 2018,the precipitation in the Malian River Basin decreased slightly,the temperature increased significantly.The runoff decreased,and the sediment transport decreased significantly.The runoff suddenly changed in 2003,and the sediment discharge suddenly changed in 2006.Runoff and precipitation have good correlation and consistency.The contribution rates of precipitation to the reduction of runoff and sediment transport were 29.61%and 31.51%,respectively,indicating that precipitation has a significant impact on runoff and sediment transport.（2）The SWAT model was used to simulate the runoff and sediment discharge in the Malian River basin.The evaluation indicators R2 and Ens of the runoff and sediment discharge during the regular and validation periods were both greater than 0.75.The observed and simulated values had a good fit and a consistent trend.Therefore,SWAT model has good applicability in simulating runoff and sediment changes in the Malian River basin.（3）The GCHP project can effectively reduce runoff and sediment transport,which is beneficial for alleviating soil erosion in the Loess Plateau and gully areas within a certain period of time.The numerical simulation results indicate that the ditch head landfill project has the most significant water and sediment reduction effect after one year of implementation,with a water reduction rate of over 10%and a sediment reduction rate of over 15%in the simulated ditch head area.However,as the time scale increases（around 3 years）,the water reduction rate decreases to 7.5%,and the sediment reduction rate decreases to 13.8%,indicating that by this time,the buried gully head has been severely eroded.Therefore,timely maintenance of the landfill project is necessary,otherwise its water and sediment reduction effect will be significantly reduced.On site monitoring found that sub watersheds with good vegetation coverage have significantly lower sediment yield.（4）The simulation found that with the increase of time scale,the water and sediment reduction effects of the GCHP project（gully head landfill）showed a gradual downward trend under different climate change scenarios（SSP126,SSP245,SSP370,and SSP585）.After the implementation of the landfill project,the inner diameter flow and sediment transport have significantly decreased within 10 years,with a water reduction rate of over 4%and a sediment reduction rate of over 10%at the simulated ditch head.However,with the increase of time scale（>10 years）,the protective ability of landfill engineering on the plateau surface weakens,and the water and sediment reduction rate significantly decreases.According to the numerical simulation results,it is predicted that without manual intervention,the ditch head landfill project will lose its water and sediment reduction effect after approximately 26 years.To ensure that the ditch head landfill project can continue to play a role in reducing water and sediment,it is recommended to maintain and repair the drainage project,and carry out necessary ecological management of the landfill area. |
