Microtopography evolution of artificial digging and analysis of hydraulic characteristics

Artificial digging was accomplished comprehensively in the Loess Plateau region during summer fallow tillage period. In order to elucidate the evolution processes on erosion as well as the flow hydraulic characteristics of its complicated slope surface under the condition of continuous rainfall, this study utilizes 3-D Laser Scanner and ArcGIS. They were employed to investigate the microtopography evolution process and hydraulic characteristics under intermittent simulated rainfall, following which it offers theoretical basis for tillage practices. The results demonstrate the following:① There are three processes which are splash erosion and sheet erosion stage, the formation of rill stage and the developing of rill stage. The rill density, average depth, maximum rill length and depth increased by 1.42, 1.72, 15.57 and 3.18 times as against initial rill forming stage with rainfall. ② The initial surface roughness of artificial digging is 1.706 which decreased linearly to 1.488 with the rainfall. In the process of accumulated rainfall reaching 81 mm, the runoff and sediment yield increased slowly with the decline of roughness, but increased dramatically later. ③ The flow velocity with fluctuation increased after the rill shaping, and the flow advanced from laminar to turbulent flow speedily, but keeping the subcritical flow all the way. Under the effect of surface roughness, the flow resistance comprised of grain resistance, rain resistance and form resistance which decreased with the rainfall duration, where the form resistance took the most significant position during the entire process. The slope surface of artificial digging might have a positive impact on soil and water conservation under the rainfall intensity of 1.5 mm/min when the rainfall is within 80 mm, but it may prone to suffer rill erosion under continuous extreme rainfall.