A Analysis Of Slope Algorithms And Its Effects On Soil Erosion Simulation Based On DEM Of Yuanmou Gully

Soil erosion has a great influence on human survival,social stability and economic development.Yuanmou dry-hot valley belongs to fragile ecology regions in the southwest of China.Gully erosion is one of the typical landform of Yuanmou dry-hot valley areas.As a result of the severe soil erosion,ecological environment of this region is deteriorating drastically.A mass of gullies are generated in this region,leading to uncovered land surface in the condition of serious soil erosion.Reviewing the research of predecessors based on the gully of Yuanmou dry-hot valley,we can found that,existing researches concentrated mainly on morphological characteristics of gully,spatial distribution pattern of gully,gully erosion process,the soil properties,vegetation and precipitation characteristics and so on.After the summary,it is found that the study for topographic factors,slope gradient for example,is relatively less.Therefore,the study selects some typical gullies of Yuanmou dry-hot valley with typical morphological characteristics and erosion characteristics as research objects.Then calculating the slope gradient of gullies by four different slope algorithms.Based on different slope algorithms,USPED model is used to simulate the amount of soil erosion and soil deposition respectively.The technology and methodology of GIS,geomorphology,hydrology and statistics are used to analyze the slope gradient difference of four different slope algorithms.The simulated result of USPED model is analyzed comparatively under circumstance of different slope algorithms.The effects of slope algorithms on the simulated results of USPED model are analyzed.The main contents and contributions of this dissertation are summarized as follows:1.In January 2016 and January 2017,based on Yuanmou dry-hot valley,we made a field investigation at Shadicun and Jinleicun Tutujiliang.Gullies of the two areas are clumped distribution,and the main morphological characteristics,soil properties,vegetation types and erosion characteristics of gullies were observed and recorded.With the purpose of selecting some gullies with typical morphological characteristics and erosional characteristics to study,finally,four typical gullies were elected.There were two gullies located in Shadicun,and the other two gullies were located in Tutujiliang among it.The elevation point cloud data of four gullies were measured and acquired by the technology of three-dimensional laser scanner and GPS.In the process of measurement,according to actual terrain features of gullies,gullies were scanned with multi-site and multi-angle by three-dimensional laser scanner to obtained elevation sampling points.2.The elevation point cloud data of sample gullies was handled by the visualization software of RiSCAN PRO,mainly including point cloud registration,vegetated filter,point cloud filter,accuracy rectifying and data thinning.Inverse distance weight interpolation(IDW)was used to generate the DEM of all gullies.Ultimately,four DEMs of typical gullies were obtained.Grid sizes of all DEM were 0.05 m.3.The methods of three-order finite difference(3FD),three-order finite difference weighted by reciprocal of squared distance(3FDWRSD),three-order finite difference weighted by reciprocal distance(3FDWRD)and 5-node second-order finite difference(5N-2FD)are used to calculating slope gradients of four typical gullies.The differences of four slope algorithms are comparatively analyzed.The results show that,the maximum slope gradient,mean slope gradient and standard deviation of 5N-2FD model are higher than other models on the whole.5N-2FD model is more beneficial to describe the local slope characteristics of gully with respect to others.In three slope algorithms on the basis of third-order,3FDWRSD model is more similar to 5N-2FD model than other three-order slope algorithms.4.Based on USPED soil erosion model,the amount of potential erosion and deposition of every gullies is simulated with channel erosion and slope erosion respectively in the condition of different slope algorithms.The result shows that,the simulated potential erosion amount and deposition amount are mainly distributed in the main drainage network of gullies.The total area of erosion is greater than the total area of deposition for all slope algorithms.5.The differences of soil erosion simulated results in the condition of four slope algorithms are discussed.The result shows that,the simulated amount of potential soil erosion and soil deposition in the condition of 5N-2FD model are much higher than other slope algorithms.In terms of soil erosion amount,3FD model has a smaller difference than other third-order models compared with 5N-2FD model.In terms of soil deposition amount,3FDWRSD model has a smaller difference than other third order models compared with 5N-2FD model.For gullies of Tutujiliang,3FDWRSD model is more similar than other third-order models on the whole compared with 5N-2FD model according to coefficients of relative difference.6.Combined comparative analysis results of four different slope algorithms and soil erosion simulated results,3FDWRSD model and 5N-2FD model are similar on the whole by the reference of 5N-2FD model.Slope algorithms with 3FDWRSD model and 5N-2FD model are analyzed quantitatively.The result turns out that,except the gully of TTJ1,for other gullies,the soil erosion simulation results calculated by USPED with 3FDWRSD model and 5N-2FD model have a clear linear relationship because their multiple correlation coefficients are more than 0.8.