| The tile-back slope is common in the loess hilly area.The terrain has a natural water and sediment supply channel,which is very likely to cause serious soil erosion,reduce the quality of cultivated land.The scientific issues of how the erosion of matter,energy and morphology evolved during erosion of this special geomorphological featureare still in urgent need of further study.Therefore,this study takes the tile-back shallow sloping slope in the loess hilly and gully area as the research object.Under the condition of artificial rainfall simulation and solid model construction,the photo-three-dimensional reconstruction technique is used to study the erosion pattern of the shallow-ditch system on the tile-back slope.The evolution,the proportion of erosion methods,the contribution rate of erosion and the spatial and temporal distribution;quantify the temporal and spatial changes of erosion indicators during the development of slope channel;explore the interaction between morphological indicators and runoff and sediment yield and flow rate.The main findings are as follows:(1)The erosion process of the entire ephemeral gully system can be divided into two stages:The first stage groove depth is 10-30 cm,and the average depth of the measured groove at this stage varies from 29.3 to 28.4 cm.The second stage groove depthis 30-50 cm,and the average depth of the measured groove at this stage varies from 31.6 to 39 cm.The ephemeral gully groove erosion process is divided into three stages: In the first stage(initial),the channel deep-cutting rate > the gully-wall collapse rate > the ephemeral gully headcut rate;In the second stage(medium term),the gully-wall collapse rate > the channel deep-cutting rate >the ephemeral gully headcut rate;the third stage(late stage),channel deep-cutting rate >ephemeral gully headcut rate >gully-wall collapse rate.(2)Both the gully density and the gully dissection increase with the increase of the rainfall.The width-depth ratio of the 15° and 20° slopes is greater than 3,and the width and depth ratio of the groove of the 25° and 35° slopes less than 1.It shows that the gully-wall collapse erosion of the 15° and 20° slopes is greater than the undercut erosion,andthe 25°and 35° slopesare the opposite.(3)Comparing the calculated sediment with the measured sediment,it is found that the first calculation error is up to 22.75%,then the error is gradually reduced,and the minimum error is 5.4%.The first five events of rainfall calculation error are positivevalue,and the last three fields of rainfall error are negative value.Therefore,3D image reconstruction technology can be applied to soil erosion research.(4)The contribution rate of channel erosion to the total erosion of ephemeral gully system was 72.87%,andthe contribution rate of the ephemeral gully erosion to the total erosion of channel erosion was 49.38%.The erosion area of ephemeral gully groove contributed 44.68%to the total area of gully erosion.(5)It was found that the gully density and the gully dissection degree can be well fittedto the runoff rate as a quadratic function with a coefficient of determination of 0.941 and0.988.The degree of gully dissection can be fitted to the sediment yield very well as a cubic function with a coefficient of determination of 0.955 and 0.976.The average flow velocity is positively correlated with gully density,gully dissection degree and sediment concentration.The determination coefficients are 0.707,0.731 and 0.71,respectively. |
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