Study On The Process Of Landform Evolution Of Slope Farmland In Purple Hill Region Based On UAV High Resolution Image

Tillage erosion and water erosion were two significant soil erosion types in the slope farmland.Tillage erosion would change the microtopography after long period of tillage operations,meanwhile,it would affect the water erosion process by the change of flow velocity,flow surface width,flow depth,and flow temperature.Tillage erosion and water erosion interaction and mutual influence in the slope farmland.The orthophotos and elevation dense cloud data would be generated by unmanned aerial vehicle(UAV)close-range photogrammetry technology.Using high resolution digital elevation models(DEMs)to monitor the topographic evolution before and after tillage experiments and scouring experiments was proved to be a feasible and efficient method.Couple analysis of unmanned aerial vehicle close-range photogrammetry technology and flow hydraulic properties would reveal the soil erosion mechanisms properly.To determinate tillage erosion rate and water erosion rate in purple soil of sloping farmland under different slope gradients,a series of simulated tillage experiments(5-,10-,and 15-operation tillage)were conducted on 5°,10°,and20°sloping farmland.Then a series of scour experiments with water discharge of 60 L/min were carried out under those slopes.First,close-range photogrammetry technology was used to monitor the landform changes of sloping farmland in purple soil before and after experiments,and the best method to generate the high resolution DEMs were adopted by the comparison of schemes.Then the DEMs were used to calculate the net soil loss volume.Meanwhile,erosion pins were used to verify the accuracy of close-range photogrammetry technology by measuring the depth variation of soil layer.At last,the flow velocity,flow surface width,flow depth and water temperature were measured to calculate the runoff hydraulic properties under different slope gradients and tillage intensities.The flow energy consumption and landform change data coupling analysis was used for the slope farmland soil erosion process.Results showed that no significant differences in the DEMs accuracy could be found among various interpolation methods due to the high density of cloud data using unmanned aerial vehicle close-range photogrammetry technology.The close-range photogrammetry technology was reliable and efficient to monitor landform changes and calculate the soil erosion rates.The calculated results of DEMs were similar to those of erosion pins.The average tillage erosion rates of purple soil in cultivated slope farmland were estimated at 69.85,131.45,155.34 t/(hm~2·tillage pass)under 5°,10°and 20°,respectively,using simulated tillage experiments.The tillage erosion rate showed an increase trend with the increase of slope gradient,while the tillage erosion rate showed a decrease trend with the increase of tillage intensity.The average water erosion rates of purple soil in cultivated slope farmland were estimated at 1 892.52,2 961.76,4 405.93t/(hm~2·h)under 5°,10°and 20°,respectively,using scour experiments.Those results indicated that water erosion rate was positively related to the slope gradient.Meanwhile,water erosion rate showed an increasing trend with the increase of tillage intensity,indicating that tillage erosion would accelerate the water erosion.The spatio-temporal variation of hydraulic properties of different parts were not the same under different slope gradients and tillage intensities.The results provided a new technology to monitor the landform change under different slope gradients and tillage intensities,offering technical support and data foundation to soil erosion studies in purple soil of sloping farmland under tillage erosion and water erosion.