Experimental Study On The Characteristics Of Grassland Runoff And The Effect Of Runoff Reduction

With the development of modernization,China is faced with problems such as water resources pollution,water resources shortage and urban waterlogging.So the sponge city construction came into being.The grass plays an important role in low impact development methods,such as rain garden,ecological wetland or green roof and other measures.The grass can greatly store and regulate rainfall runoff,increase the rainwater infiltration,reduce runoff,which can alleviate the corresponding problems of water resources to a certain extent and reduce the risk of city waterlogging.Therefore,it is of great significance to study the influence of different factors on the flow and infiltration of typical grassland.It will be better for us to understand the hydrological effect of grassland and to take advantage of the effect of runoff reducing in lawn green space.In this study,the purple soil was used as the tested soil,and simulated rainfall experiments were conducted.The effects of different rainfall intensities(0.38,0.75,1.1mm/min),slopes(5,10,15,20)and vegetation coverage(0%,25%,50%,75%,100%)on the runoff and infiltration of the slope were studied.The difference of runoff between grassland and bare land is obtained,and the reduction and delaying of runoff on different slopes are obtained.The main conclusions are as follows:(1)No matter the bare land or the meadow,the initial runoff time is negatively correlated with rainfall intensity and slope.When the slope is a constant,there is a power function relationship between the initial runoff time and rainfall intensity in bare land.Under the condition of grassland,there is an obviously logarithmic function relationship between the initial runoff time and the gradient,and it decreases linearly with the increase of rain intensity.Under the same rainfall intensity and gradient,the initial runoff time of grassland is lagging behind that of bare land.With the increase of rainfall intensity and slope,the delay value of grassland's initial runoff generation time decreases.Under the condition of0.38mm/min and 5 degrees,the time for the initial runoff production to delay is the longest,reaching 12.95min.When the rain intensity is 1.1mm/min and 20 degrees,the delay time of the initial runoff time is the shortest,which only delays 1.18min.(2)No matter what intensity of rain,slope and vegetation coverage,the trend of runoff on the slope is basically the same with the rainfall duration.It can be divided into four stages:the initial runoff stage,the rapid increase stage,the slow increase stage and the stable stage.No matter grassland or bare land,when the slope is certain,the stable runoff intensity of slope increases with the increase of rainfall intensity.In the bare land,under a certain rainfall intensity,a parabolic relationship between slope stable runoff intensity R and slope?is R=?~2+b??+c.The stable runoff intensity of grassland is more complicated with the change of slope.Under 0.38mm/min and 0.75mm/min,the stable runoff intensity increases first and then decreases with the increase of slope.When the rainfall intensity is 1.1mm/min,the peak runoff of grassland decreases with the increase of slope.In the same rainfall intensity,along with the slope increases,the difference of peak flow between the grassland and bare is more complex.When the rainfall intensity is 0.38mm/min,the difference of peak flow between the grassland and bare decreases with the increase of slope,the effect of weakening the peak flow rate decreases;when the rainfall intensity is0.75mm/min,stable runoff rate is little different with the slope change;1.1mm/min,the peak flow gap between the grass and bare land firstly increases and then decreases with the increase of the slope.Under the same slope condition,the gap between the peak flow rate of the grassland and the bare land increases with the increase of the rainfall intensity.In the process of rainfall,the cumulative runoff and rainfall duration showed obvious linear function relationship.And in the same slope conditions,the growth rate of cumulative runoff differences each other because of different rainfall intensities.Under the same conditions,the speed of runoff growth rate on bare slope is higher than that of grassland.In both bare land and grassland,the runoff volume increased significantly with the increase of rainfall intensity,but the runoff of grassland is less than that of bare land under the same conditions.The decrease of runoff is increased with the increase of rainfall intensity according to the total amount runoff of bare land runoff and grassland.(3)Whether the grassland or bare land,when the slope is constant,the stable infiltration rate increases with the increase of rainfall intensity.In the grassland,when the rainfall intensity is 0.38mm/min or 0.75mm/min,the infiltration rate decreases firstly and then increases with the increase of the slope;in 1.1mm/min rainfall intensity,stable infiltration rate increases with the increase of slope,but the increase with the slope changes little.Under bare land,the stable infiltration rate will decrease first and then increase with the increase of the slope.The sod can increase the infiltration rate.When the slope is certain,the difference of stable infiltration rate between the two kinds of lands increases with the increase of rainfall intensity,but the increase is different at different slopes.When the rainfall intensity is certain,the difference of infiltration rate between the grassland and the bare land is more complicated with the gradient.When the rain intensity is 0.38mm/min,the difference value between the grassland and the bare land is decreased with the increase of the slope;when0.75mm/min,the difference value of the steady infiltration rate increases with the increase of the slope;while the rain intensity is 1.1mm/min,the difference of the steady infiltration rate increases first and then decreases.(4)When the rainfall intensity is certain,the initial runoff time increases with the increase of the coverage.That is,the initial runoff time of the bareland is shortest,the initial runoff time is the longest under the condition of full cover.The steady runoff intensity decreases with the increase of vegetation coverage,and there is a linear function between them.The infiltration process of different coverage gradient is basically the same as time,which is divided into initial infiltration,rapid growth,slow growth and stable stage.The flow rate under a certain rainfall intensity decreases with the increase of cover coverage,and the cumulative runoff changes linearly with time,and its growth rate is proportional to the intensity of rain.Under certain rainfall intensity,the slope stability is increased with the increase of vegetation coverage.