| Slope rainfall runoff regulating is the unique and significant method to solve the drought and water shortage and soil erosion problem. This study based on different biological regulating, through field artificial rainfall simulation experiment, comparatively systemic analysised the change law of slope rainfall runoff, soil infiltrations and overland flow hydraulic parameters. The main conclusion of this paper as following:1. Biological measures are closely related to slope rainfall-runoff threshold.Biological measures enhance the difficulity of runoff yield and increase the slope rainfall-runoff threshold. The results show that, the rainfall-runoff thresholds received by linear regression method for each slope were as following: bare slope 9.4mm, ryegrass 23.6mm, purple medic 19.5mm and spring wheat 15.8mm respectively. After considering the rainfall intensity, vegetation coverage and the antecedent soil water content, the rainfall runoff thresholds became bare slope 13.4mm, ryegrass 23.7mm, purple medic 18.8mm and spring wheat 19.7mm respectively.2. Biological measures could increase significantly the capacity of soil infiltration.The results show that,the stable infiltration rate of bare land is least, with the average of 0.3862mm/min, while compared to bare slope, these of ryegrass, spring wheat, purple medic were raised by 90.9%,69.5% and 61.1%. The soil stable infiltration rate increased firstly and then decreased with the increase of rainfall intensity and slope degree; there exists an "critical rainfall intensity"and "critical slope" value. The critical rainfall intensity values of each slope were: ryegrass 2.52mm/min, spring wheat 2.10mm/min, purple medic 1.97mm/minand bare slope1.57mm/min; critical slope degree of each slope were ryegrass 11.87°, spring wheat 12.13°,purple medic 11.63°,bare slope 9.44°.Vegetation coverage can raise the soil stable infiltration rate, before reached the critical vegetation coverage (ryegrass 67%,spring wheat 57% and purple medic51%), increase rate of stable infiltration rate went up quickly with the increase of vegetation coverage, after reaching the critical value, increase rate reduced and towards to stability.3. Biological measures could postpone significantly the time of runoff yield and decrease the runoff intensity mean. The results show that, the time of runoff yield and the runoff intensity mean were the following respectively: ryegrass 12.28min, spring wheat 8.53min, purple medic 5.68min, bare land 3.33min and ryegrass 0.3003mm/min, spring wheat 0.4735mm/min, purplr medic 0.4695mm/min, bare land 0.6639mm/min.And the variance analysis indicate that effects of different biological on the time of runoff yield and the runoff intensity mean reach the highly significant level (Prob=0.01).There are the significant linear relationship between the runoff intensity mean and rainfall intensity, slope gradient, antecedent soil water content.The impact of antecedent soil water content on the runoff intensity mean is the biggest (The runoff intensity mean will increase: bare land 5.0208,purple medic 3.0309,spring wheat 2.3083 and ryegrass 2.3032 units, when antecedent soil water content rise 1 unit);the following is rainfall intensity (The runoff intensity mean will increase: bare land 0.7163,purple medic 0.4891,spring wheat 0.4259 and ryegrass 0.3610 units, when rainfall intensity rise 1 unit);and the impact of slope gradient on the runoff intensity mean is least(The runoff intensity mean will increase: bare land 0.0689,purple medic 0.0479,spring wheat 0.0319 and ryegrass 0.0336 units, when antecedent soil water content rise 1 unit).The runoff intensity mean decrease with the increasing of vegetation coverage by negative exponent way, but the reduced rate minish continually. Before the value of vegetation coverage: purple medic 51.62%,spring wheat 62.16% and ryegrass 72.72%,the reduced rate of the runoff intensity mean decrease quickly. However, after this vegetation coverage, the reduced rate is fast decreasing for corresponding slope.4. There are significant effects of biological measures on mechanical parameters of the overland flow. The results show that, the mean flow velocity and the mean water depth of bare land, purple medic ,spring wheat and ryegrass are respectively: 3.98cm/s,2.46cm/s,2.25cm/s,1.90cm/s and0.34mm,0.42mm,0.51mm,0.82mm.And the mean Froude number and the mean Manning roughness coefficient of bare land, purple medic ,spring wheat and ryegrass are respectively: 0.71,0.36,0.22,0.17 and 0.05,0.11,0.20,0.28.In addition, variance analysis show that, the influence degree of biological measures on Froude number and Manning roughness coefficient reach the significant level(Prob=0.01).There are the power function relations between flow velocity, water depth, Reynolds number, drag coefficient and rainfall intensity, slope gradient, and the exponential function relationship with vegetation coverage. In this paper, Reynolds number range from 1.88 to 36.38, and Froude number are between 0.026 and 1.346.Furthermore,most of Froude number are less than 1.According to the general rule of open-channel flow, the state of most rainfall events are slow stratified flow.
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