Research On Extraction Method Of Erosion Slope Length For Channel Interception

Erosion slope length was a cumulative length based on the principle of erosion deposition,reflecting the impact of hillslope sediment and other materials on the process of erosion,transport and deposition.The results were widely used in the prediction and evaluation of soil erosion and had guiding significance for soil and water conservation.The extraction required the determination of the initial position,intermediate process and deposition position of hillslope material transmission.The initial position was generally fixed as the local highest point on the surface.The calculation of the intermediate process was the cumulative length of slope sediment transmission,which was generally realized by the flow direction algorithm.The sedimentation position mainly considered the open channel and small watershed channel in the terrain.The existing extraction accuracy of erosion slope length was affected by the error of flow direction algorithm and the accuracy of channel extraction,and the spatial distribution accuracy of extraction results still needed to be improved.Therefore,this study started from the key steps of erosion slope length extraction.First,open channel and small watershed channels in the terrain were extracted to determine the channel interception position of erosion slope length.Then,the transmission process of erosion slope length was optimized by modeling analysis,and the extraction method of erosion slope length oriented to channel interception was designed.The main research contents and results were as follows:(1)Research on extraction method of open channelRaster digital elevation data was used to label open channel with clear visual interpretation,and open channel data set for semantic segmentation was constructed.Then,based on the mainstream segmentation model for preliminary training,CGNet was selected as the segmentation model based on the accuracy of the results and the lightweight of the model.In order to further improve the segmentation accuracy,aiming at the information fusion part of CGNet,CBAM attention module was used to enhance the beneficial features,and an AIM-CGNet lightweight segmentation model with 0.66 M model parameters was constructed.The segmentation accuracy of MPA,MIo U and FWIo U reached 94.76%,89.95%and 94.88% respectively in raster digital elevation open channel data set,which were 1.08%,0.42% and 0.74% higher than CGNet,respectively.The method can extract open channel efficiently and accurately.(2)Research on extraction method of of small watershedAiming at the small watershed gully with unclear visual interpretation,a gully extraction method was designed.Firstly,the candidate areas of gully were extracted by using flow simulation method and geometric analysis method.Then,the difference between upstream and downstream of each tributary segment was divided by using contour clustering method,and the location of gully head was determined according to the cluster boundary.Based on the location of gully head,the extracted gully skeleton candidate area was pruned and defined to extract the complete small watershed gully.Compared with FAT method and DNE method,which were more influenced by user experience parameters,the calculation process of the proposed method did not require user input parameters,and the test results of the proposed method were optimal on small sample channel head data in the field.The reliability of the proposed method was 0.667,and the sensitivity was 0.571.The proposed method can realize the effective extraction of small watershed without relying on expert experience parameters.(3)The extraction method of erosion slope length for channel interceptionIn view of the errors in the existing extraction methods of erosion slope length,the source analysis was carried out,and the calculation model was reconstructed on the ideal surface according to the basic definition of erosion slope length.The objective function and constraint conditions of erosion slope length were set up,and the Integration of Topographical Features(ITF)erosion slope length extraction method was proposed based on the differential equation of slope runoff model and its numerical solution.Through simulation experiments on mathematical surfaces,compared with slope length extraction methods based on D8,Dinf,MS and MFD-md flow direction algorithms,the error of ITF algorithm was the smallest,relative root mean square error of the designed flat slope,divergent slope and converging slope were 0.061,0.014 and 0.075,respectively.Fixed-point analysis and statistical results on complex surfaces showed that the ITF algorithm can effectively reduce the overestimation of cumulative slope length(especially on strongly divergent hillslopes).The channel results extracted from open channel and small watershed were taken as the channel interception condition of erosion slope length.In the actual terrain test,the spatial distribution of erosion slope length extracted by ITF algorithm was in good agreement with the morphological details of the surface,which had strong physical interpretation significanceBased on the studies in(1),(2)and(3),an effective channel interception-oriented erosion slope length extraction scheme was proposed,which can take into account different channel lengths and widths.The designed erosion slope length extraction method effectively reduced the calculation error,and the spatial distribution was highly consistent with the terrain details,and the numerical interpretation was clear.It provided effective technical support for soil erosion evaluation and precise control of soil and water conservation.