A Analysis Of Flow Direction Algorithm And Its Effects On Soil Erosion Simulation Based On DEM Of Loess Gully

Severe soil erosion will cause damage to soil tillage layer and decrease productivity.If a large amount of sediment generated in this process flows into the river,it may cause problems such as stream upflow,siltation of water conservancy projects,and even floods and droughts.Soil and water conservation research and the prevention and control of soil erosion are necessary for the ecological environment,human activities,and social and economic development.The development of soil erosion research and in-depth study on soil erosion prevention and control are significantly exemplary.In soil erosion research,soil erosion model is used as an important method to quantitatively simulate soil erosion and a guiding tool for soil and water conservation practice,and it is continuously developed and updated with the expansion of research,and the results are very significant.Soil erosion simulation and prediction of soil erosion model are related to soil erodibility,gradient,slope length,rainfall,catchment area,vegetation cover and crop management,but whether the difference of flow algorithm will affect the forecast of soil erosion model? Does soil erosion,sedimentation,and numerical differences occur in soil erosion simulations? How to compare and describe quantitatively? Further exploration and discussion is needed.The soil erosion is serious in the Loess Plateau,the main sediment-yielding area in China,where the gully has many developments and features.This study selected the Loess Plateau as the research object,and selected four combinations of loess gullies(dendritic gullies,comb gullies,lattice gullies,parallel gullies)to construct DEM data.And to compare different flow direction algorithms in soil erosion prediction in the similarity,soil erosion and sedimentary eigenvalues,soil erosion and sedimentation area ratio,and soil erosion and sedimentation misclassification probability of the model(Power Stream-based Erosion Deposition,USPED).The main contents and conclusions of the study are as follows:(1)The effects of different combinations of gullies on the catchment area under different flow directions algorithms are explored.In general,the distribution of river network of each combined form gully under a variety of flow direction algorithms presents roughly consistent visual characteristics,but there are differences in the value of catchment area.When the value of regional catchment area is low,the D8 algorithm and the Rho8 algorithm produce small and dense parallel flow paths,while the Dinf algorithm and the MFD algorithm distribute the flow more evenly.However,for each type of gully,the flow direction algorithm has different results for the catchment area.The Rho8 algorithm in the dendritic gully differs most from the D8,Dinf,and MFD algorithms,and the Dinf algorithm and the MFD algorithm have the highest similarity.The influence of the flow direction algorithm in the comb gully on the catchment area is less difference in the calculation of the relative difference coefficient,but it has more difference in the correlation of catchment area.At the same time,similar to dendritic gully,comb gully,lattice gully and parallel gully all show that the catchment area results of Rho8 algorithm are significantly different from the other three flow direction algorithms,and the similarity between Dinf algorithm and MFD algorithm is the highest.The similarity of the catchment area results of the two multi-flow algorithms is also the embodiment of the algorithm mechanism.In general,the four flow directions have similarities in the catchment area results in different combinations of gullies.As far as possible,Rho8 algorithm should not be selected in the flow direction algorithm for calculating the catchment area of loess gully involved in this study.(2)Soil erosion simulation under different flow direction algorithms was conducted based on the USPED model,and the spatial distribution of soil erosion and sediment prediction of gully with different forms was nearly consistent.As the result of the cumulant accumulation is affected by different factors such as the width and size of the flow path,there are differences in the soil erosion simulation situation in terms of small morphology.The differences in soil erosion simulation results are mainly reflected in the numerical value of soil erosion and sediment.(3)Soil erosion simulation results of loess gully can be found in different areas: soil erosion area is larger than sedimentary area;the sum of soil erosion area and deposition area simulated by D8 algorithm is the smallest,while the MFD algorithm is the largest.The D8 algorithm and the Rho8 algorithm have similar ratios of erosion area and deposition area,while the Dinf algorithm is similar to the MFD algorithm.The mean of soil erosion simulation is negative and the mean of sediment is larger than the mean of erosion.The misprision probability of soil erosion simulation also shows that the value of D8 algorithm and Rho8 algorithm is small,that of Dinf algorithm and MFD algorithm is small.The Rho8 algorithm and the Dinf and MFD algorithms have higher soil erosion simulation misclassification probability than the D8 algorithm.(4)The effects of soil erosion simulation brought by the difference of flow direction algorithm were analyzed quantitatively.Simulation results of dendritic gully soil erosion: the overall difference between the similarity upper flow algorithms is small,and the Rho8 algorithm has the lowest similarity with the simulation results of the other three algorithms.The misclassification value of the Rho8 algorithm and the Dinf and MFD flow direction algorithms in the soil erosion misclassification probability is greater than the D8 algorithm and the values of the two algorithms;Dinf algorithm has many differences in the statistics of characteristic values of soil erosion simulation,but they are similar on the whole.The results of soil erosion simulation of comb flow gully multi-flow algorithm are quite different,and the Rho8 algorithm has the lowest similarity with the three flow direction algorithms.The mean soil erosion simulated by the MFD algorithm is quite different,While compared with other flow direction algorithms,Rho8 algorithm has the highest probability of soil erosion misclassification.Simulation results of soil erosion in grid-like gullies: the simulation results of the four flow directions are better in similarity.The numerical values of soil erosion simulation characteristic values,misclassification probability and area ratio are represented by two similar characteristics of D8 algorithm and Rho8 algorithm,Dinf algorithm and MFD algorithm.Simulation results of soil erosion in parallel gully: Compared with D8 algorithm,Rho8 algorithm has lower similarity than Dinf algorithm and MFD algorithm;MFD algorithm shows more differences with other three algorithms in soil erosion simulation eigenvalues.The probability of soil erosion misclassification and the ratio of soil erosion and sediment area are similar in the single flow algorithm and the multi-flow algorithm.In general,the soil erosion simulation results of D8 and Rho8 algorithms,Dinf and MFD algorithms are similar.There are many differences between Dinf algorithm and MFD algorithm in soil erosion simulation eigenvalues.It is not recommended to select Rho8 flow direction algorithm for soil erosion simulation.