Hydrodynamic parameters and their relationships of runoff over engineering accumulation slope

Abstract: Engineering accumulation generated during the process of engineering construction has a unique soil composition and complex underlying surface. This sort of deposit is characterized by weaken anti-scourabilty attributed to loose texture, which may result in the runoff conditions easily causing severe soil erosion. Hydrodynamic parameters and their relationships of runoff from steep engineering slope show different characteristics in response to hydrodynamic conditions. A detail study of the hydrodynamic characteristics is a premise and foundation to understand erosion processes on engineering accumulation. For this reason, a field study was conducted for the simulation of erosion process by runoff in order to reveal the mechanisms of erosion by runoff on engineering accumulation slope. Flow patterns and the characteristics of hydrodynamic parameters were investigated by studying runoff velocity, depth, Reynolds number, Froude number, resistance coefficient, flow shear stress, stream power and other relevant parameters and analyzing the spatiotemporal variations of the main hydrodynamic parameters and their relationships. The study area is located in the Changwu Agricultural Ecological Experimental Station on the Loess Plateau (35°14′24.5″N, 107°41′21.24″E). The established plot was 20 m long and 5 m wide, with 0.5 m thickness of soil generated from slope excavation. Weeds and organic residues were cleaned away at beginning. Three slope degrees of 24°, 28° and 32° and 4 flow rates of 30, 40, 50 and 60 L/min, a total of 12 field trials, were designed in this study. Results showed that in the processes of erosion by runoff on the engineering accumulation, dramatic changes of the Reynolds number and resistance coefficient were observed in the upper slope (0-10 m) in 12-30 min after runoff generation. For the Froude number, the dramatic change was found in the lower slope (6-18 m) in 0-18 min after runoff generation. Flow shear stress and stream power abruptly increased in the upper slope (0-10 m) in 12-30 min after runoff generation. In the slope range from 24° to 32 °, velocity increased with slope degree and flow rate and their relationship can be expressed by a binary linear equation. The Reynolds number was positively correlated with the resistance coefficient. The Froude number had an exponentially negative correlation with resistance coefficient. Under the experimental conditions of slope degrees and flow rates, the rill erodibility of engineering accumulation was calculated to be 2.63×10-2 s/m for shear stress and 0.1 s2/m2 for stream power. The critical stream power for rill erosion occurring was 0.8 N/(m·s). A large number of production projects will inevitably lead to a large amount of dregs and thus, a key measure to prevent engineering accumulation should impound runoff timely and effectively. In this paper, we obtained primary location and main periods of slope erosion by the field simulation of erosion on engineering accumulation slope. Meanwhile, fitting the relations of hydrodynamic parameters to soil erosion rate, rill erodibility and critical runoff power can also provide basic parameters for the construction of soil erosion model in engineering accumulation. Limited by the field conditions, the experiment had some shortcomings. For example, selected section was less intensive, time interval for measuring was not precise enough, and the determined values for the spatiotemporal variation of erosion were only a rough range.