Study On The Effect Of Land Cover And Gully Engineerings On Runoff And Sediment Regulation In Typical Watershed On Loess Plateau

Loess Plateau with heavily soil erosion is limited in water resources and sensitive to hydrological environment,especially,this fragile ecological environment has a deep affect on the harmonious development of social economy,natural resources and eco-environment.At Present,many of massive ecological constructions aimed at soil and water conservation have been executed.Research on typical watershed sedment and runoff and their synergistic changes based on land use change(LUCC) and the building of gully engineerings.It has an important theoretical significance of land use planning and management and environmental constructions in Loess Plateau.This thesis was carried out in Anjiagou watershed in loess hilly-gully region.Based on the methods of GIS&RS technical,landscape ecology,systemic hydrological observation,and the information data of land use of 1987,1997 and 2007,hydrology and meteorology,mathematical statistic methods and so on,this thesis analyzed the land use change and its driving force system,the different heterogeneities of precipitation distribution,and deeply studied the the dynamics response of land use change to sediment and runoff in typical watershed in Loess Plateau.And we studied the benefit of different water and soil conservation measure to block the sand.The conclusions are as follows:In the basin,The inter-annual rainfall distribution of the Basin is uneven,multi-year average precipitation is 414.4mm,the maximum precipitation in 2003 is 536.5 mm,the lowest precipitation in 1997 is only 312.8mm;the distribution of precipitation in the basin during the year is June to September, and the precipitation in July and August accounted for 61.16%of the annual rainfall.the spatial distribution of precipitation is Uneven,surface deviation Cv value of the average coefficient is 0.56. In Different precipitation level year,the frequency of various types of heavy rains are different,the frequency of type A,B heavy rain in normal rain year and in wet years are higher,and the frequency of type C heavy rain in wet year is higherBy the analysis of the correlation of erosion and rainfall factor,the results show that the correlation of erosion and rainfall factor tchanges together,such as k_e,EI₃₀,p,andâ… ,under the conditions of different scales.The correlation of rainfall kinetic energy Ke and erosion is better in all scales.On the basis of three rainfall stations Formation of rainfall kinetic energy data,spatial interpolation through the establishment of Anjiagou Basin in 1987-1997 and 1998-2007 rainfall kinetic energy of the two courts, USLE equation was used to calculate the erosion modulus of the basin,The max-relativity region of rainfall kinetic energy and sediment of opening of the basin is the vicinity of the middle reaches in the basin,gully erosion and sediment yield in the basin occupies an important position,and in opening basin areas,the terrain is relatively flat,especially in recent years,a very good returning farmland to forest(grassland) projects has implemented,so erosion modulus is also smaller,and it is not sensitive to rainfall erosivity.According to the simulated results by SWAT model on the base of yearly step,the simulated mean annually runoff has the best veracity,a correlation coefficient of annual runoff is 86.1%, Nash-Suttcliffe coefficient is 0.79;a correlation coefficient of annual sediment is 70.5%,Nash-Suttcliffe coefficient is 0.62;the veracity of simulated value in yearly step is better than that in monthly step.The veracity of monthly simulated value in rainy season is better than that in dry season.The simulated mean monthly sediment has not good veracity;Three different land cover of 1987,1997 and 2007,land use change scenarios of the basin were simulated with SWAT model,the results show that:Rainfall and land-use change had a great impact on runoff and sediment;The Month of the year with more rainfall,larger amount runoff and sediment was produced.The main land use change in the watershed is the reduction of slop land and forestland area increased,the corresponding changes in hydrological is the reduction of runoff and sediment.by using the method of fixed-a factor(climate or land-use change),contribution affection of land use and climate change to runoff and sediment were obtained.The rainfall scene scenarios result indicated that:with same land use,in rainy season,along with reduction of the rainfall amount,the runoff is influenced by rains,it's variation is large;in the dry season,the runoff does not exist,the runoff is not influenced by rains;the sediment changes along with runoff change,the runoff produced by the centralism rainfall hold massive sands,it produces large amount of sand in July and August,which occupies 60%yearly produces,the variation is larger than the amount of runoff.Therefore,we can see rainfall factor and produces primary influence on runoff and the sand t,and the influence to the silt is bigger than to the runoff.The land use scene scenarios result indicated that the runoff and sediment change scope is declining,when land use occupied 80%area in the basin.With the vegetation cover decreasing from 100%,80%,50%,20%to bare land,the runoff is rising in rainy season,the percent is 73.37%,75.07%,85.27%,87.34%and 90.80%.The scene of Loess Plateau conservation measure of water and soil result indicated that runoff control rate of the silt dam is higher in dry year,in all measures(terraced field,forest and grass,silt dam),it's area is smallest,but it reduces most of the sediment.The theses calculates various single items measure using experience way and SWAT model,and the block sand coefficient of the territory terraced field is modified as 0.80;the blocks the sand coefficient of grass and forest land is modified as 0.52.As for the Anjiagou basin which is such an arid water basin,the ecological construction projects on the Basin should be considered on the point of increasing water yield of the basin.Converting farmland for grassland should be emphasized based on containing the status of certain quantity and quality forestland.