Study On Soil And Water Conservation Effects Of Typical Small Watershed In Mountainous Area Of Central Shandong Based On SWAT Model

In recent years,rapid economic development and irrational land use,such as large-scale industrial and agricultural development,have led to the migration and loss of a large amount of soil along with surface runoff,which has brought great challenges to the management and restoration of soil erosion.The state has put forward such concepts as "ecological civilization","clear waters and lush mountains are invaluable assets" and "mountains,rivers,forests,fields,lakes,grass and sand".Soil and water conservation with the prevention and control of soil erosion as the core is one of China’s basic state policies and the central task and goal of ecological environment protection and construction.It has become a trend to carry out systematic multi-factor comprehensive research on relatively independent small watersheds.Therefore,it is very necessary to study the rainfall pattern and simulate runoff and sediment in Qilongwan small watershed,which can not only further understand the current situation of soil and water loss in this region,but also provide reference and basis for the prevention and control of soil and water loss in this region and the dynamic monitoring of soil and water loss.This has theoretical support and practical significance for the comprehensive management and construction of small watershed in the middle mountainous area of Shandong province.Aiming at the problem of soil and water loss in Qilongwan Watershed,a typical small watershed in central Shandong Province,based on the rainfall monitoring data from 2008 to2019,this paper discusses the relationship between rainfall and flow in this region,and builds SWAT model to simulate Qilongwan Watershed.The adaptability of the model was evaluated,and different land use scenarios were set up to simulate sediment production and loss under different land use scenarios,so as to further reflect the effect of soil and water conservation in Qilongwan small watershed.Finally,a series of suggestions and plans for small watershed were put forward,and the following conclusions were drawn:(1)Based on the daily rainfall data from 2008 to 2019,the monthly and seasonal distribution characteristics of rainfall were analyzed,and the distribution rules of inter-annual rainfall and inter-annual erosive rainfall were discussed.The rainfall months are mainly concentrated in June to August,and the precipitation in the other months is relatively small,and the distribution of rainfall is uneven.The rainfall months change significantly,and show obvious seasonal differences,most of the rainfall is concentrated in summer.The fitting relationship between water level and discharge is extremely significant,and the fitting curve can be used to estimate discharge.The analysis of key rainfall shows that there is a corresponding relationship between rainfall and discharge.With the gradual decrease of rainfall,the change of discharge showed an overall trend of rising first and then decreasing,and the flood peak of discharge mostly appeared within 3-12 h after the flood peak of rainfall,and the lag effect was obvious.(2)Combined with SWAT model,the spatial and attribute database of Qilongwan watershed in Laiwu was constructed.The basin is divided into 26 sub-basins and 115 hydrological response units.The dynamic changes of runoff in this region are simulated and calibrated according to the measured data.The simulation results show that the efficiency coefficient Ens of monthly average runoff simulation is 0.66,and the linear regression coefficient R2 of measured and simulated runoff is 0.92.Ens of monthly average runoff simulation efficiency coefficient in the inspection period is 0.56,and R2 of linear regression between measured value and simulated value is 0.97.This indicates that THE SWAT model can be applied to the simulation operation of sediment yield and abortion in Qilongwan watershed,and the simulation effect is good,which can provide support for the effective and accurate simulation operation of different scenarios for the basin in this region.(3)Using the SWAT model,by setting various change scenarios such as the current conditions and extreme land use of the Qilongwan small watershed,the hydrological indicators such as runoff and sediment content changes were simulated and studied.The results show that there is a certain correlation between runoff and sediment.The variation law of sediment yield is basically the same as that of runoff.Both are affected by rainfall.Seasonal changes are obvious.The difference in runoff and sediment yield of each extreme land use type is the most significant in July.The size of annual flow was as follows: scenario 1(arable land)> current situation >Scenario 3(woodland)> Scenario 2(orchard)> Scenario 4(grassland),and the size of annual sediment yield is scenario 1(arable land)> current situation > Scenario 3(woodland)> Scenario2(orchard)> Scenario 4(grassland).When the land type is mostly cultivated land,the annual average monthly production flow is as high as 1298.83 mm,and the sand production is 89.24 t.When the land use type is mostly grassland,the multi-year average monthly production flow is the smallest,which is 559.03 mm,and the sand production is 20.42 t.This shows that the surface coverage of cultivated land is sparse,and the interception ability is poor,thus increasing the amount of sediment.Grassland and woodland types have certain functions of water conservation and interception,which can promote the transfer of water in the soil,thereby reducing soil erosion and better improving the effect of soil and water conservation.The study of soil and water loss must be carried out according to the actual situation of the region.The construction of ecological clean small watershed is a further improvement on the basis of the traditional soil and water conservation work and an inevitable requirement of the construction of ecological civilization.Therefore,it is necessary to insist on returning farmland to forest and grassland,carry out land use analysis for different plots,and formulate the most suitable water and soil conservation configuration.Introducing new concepts such as "new normal" and "mountain,water,forest,farmland,lake,grass and sand" life community,advocating the development of efficient ecological agriculture,closely combining the ecological benefits and economic benefits of the basin.To build an innovative eco-clean small watershed technology measure system,focus on the two core elements of ecology and cleanliness,introduce new technologies and methods into practice,organically combine soil erosion,nonpoint source pollution and beautiful new countryside construction through certain technologies and methods,and improve the corresponding management mechanism.Based on the actual situation of regional nature and society,this thesie summarizes and analyzes the rainfall law of Qilongwan watershed,a typical small watershed in central Shandong.Based on SWAT model,the characteristics of runoff and sediment were simulated,and the changes of hydrological and ecological indicators under different land use scenarios were discussed.A series of suggestions on soil and water loss in this region were put forward,so as to provide a constructive reference for the planning and development of this small watershed.