基于三维重建技术的坡面细沟侵蚀演变过程研究

作为黄土高原地区沟头溯源侵蚀和水流汇集发源地的梁峁坡面,在强降雨下其产流产沙对沟缘线以下坡面及沟道侵蚀有着重大影响。该研究根据野外实地考查构建5°～35°变坡段实体模型,进行6场间歇性人工模拟降雨试验,并借助基于三维重建技术的PhotoScan软件获取坡面DEM,将其侵蚀演化过程进行图形化、数字化,定性定量揭示其侵蚀形态演变特征。研究表明:1)梁峁坡面细沟侵蚀历经4个阶段:面蚀阶段,即产生一系列呈串珠状分布的侵蚀跌坑,宽度5～9 cm,深度1～4 cm;细沟形成阶段,由面蚀所产生的微小跌坑在径流作用下长、宽、深均不断增大,最大分别达到266、7.6、13.8cm;细沟网形成阶段,细沟出现分叉及联通,有明显流路;小切沟形成阶段,伴随沟壁崩塌、沟壁加宽和沟底下切,最大沟长及最大沟深较细沟形成时增大3倍以上。2)对比次降雨过程基于三维建模所计算侵蚀量与实测侵蚀量,第1场降雨试验因地表疏松颗粒较多导致实测侵蚀量比建模计算侵蚀量大而引起较大偏差(20.82%),其他场次偏差均在10%左右或以下,总体来说,该技术可以较好地应用于侵蚀发育过程的研究。该研究实现侵蚀演变关键过程图形化、数字化,有助于人们定性、定量了解和认识梁峁坡面侵蚀过程,且对于创新侵蚀过程研究方法亦具有实践指导价值。

Evolution process of slope rill erosion based on 3D photo reconstruction technique

Liang-mao slope system is in the loess hilly and gully region. Its accumulated runoff and sediment production has a direct and significant impact on the slope erosion and the channel erosion below the margin line is the origination of headwater erosion and water flow under the act of heavy intensity rainfalls. In this research, we used an advanced research techniques: the three-dimensional reconstruction technology, and intermittent artificial rainfall simulation combining with soil erosion, as well as the theory of river sediment transport to express the erosion processes of slope varying from 5° to 35°. Evolving morphological parameters were used to elucidate hillslope erosion evolutionary rules and specific characteristics quantitatively. In combination with PhotoScan software and ArcGIS, the complex evolution process of soil erosion on variable gradient slope was graphed and digitalized, the evolution characteristics of morphology parameters and the relationship between detachment and morphological indicators were revealed qualitatively and quantitatively. The results showed that the evolution process of rill erosion on the loess liang-mao slope mainly experienced through four stages: The first stage was that the evolution stage from sheet erosion to rill erosion, which was often at a distance at the top of the slope had a series of eroded drop pits with the shape of beadlike and nearly equal spacing at different distances. The width of eroded pits was about 5-9 cm, the depth was about 1-4 cm with an average of 2 cm. The second stage was rill erosion development stage. In this stage, the micro rills were produced from drop pits under the interaction between water scouring and rain drops beating to the slope surface, the maximum length, width, depth and rill density of rills increased to 266, 7.6, 13.8 cm respectively. The third stage was the rill network stage in which bifurcating and merging of rills gradually formed rill network. The last stage was undercutting erosion of rills and widening of the trench walls causing rill network developing in length and depth, and finally, the micro gully erosion presented in the varied gradient slope surface. The maximum depth, length and width of rills and rill density were introduced to quantify development characteristic of rill networks and reflect the erosion intensity in vertical and horizontal direction, they all augmented with the increase of erosion amount. The hillslope gradually developed from flat to complex terrain. The results also showed that the eroded soil amount could be obtained through the value of DEM(digital elevation model) based on 3D reconstruction method before and after the rainfall runoff erosion process followed by, comparison with the actual measured subsurface rainfall erosion amount. The calculation showed that the deviation between the calculated erosion amount and the actual sediment production amount was only 20.82% at the first test, and the results of other tests varied around10%. Therefore, the technology was accurate enough to be applied in this study. The study not only can deepen people''s understanding of the qualitative and quantitative process of soil erosion development, but also have profound academic value and practical guidance value for innovative erosion process research methods and guiding slope and gully treatment guidelines.