Experimental Study Of Reduction On Typical Urban Lawn Green Surface Runoff

City lawn can effectively alleviate the city waterlogging disaster, alleviate the pressure of city drainage pipe network through its function of interception, reducing surface runoff. In order to study the runoff process of two kinds of green space and analyze the effect of green space on storm runoff reducing at different vegetation coverage(0%、90%)、different rainfall density (30、60、90mm/h) and different slope degree (5°、10°、20°) by using artificial simulated rainfall device, this paper sat the representative green space in the south and the north of China as the study object and the bare land as CK, which aimed at to relieve urban waterlogging disasters and alleviate pressure on urban drainage network, and sponge urban construction to provide theoretical and technical support. The main results are as follows:Two kinds of grassland runoff process law is similar, runoff began to produce after a period of time raining, runoff rate increased as the rainfall continue, and finally tend to be stable. The initial runoff generation time range from 2’05"to 54"00", there is a peak flow with the increasing of runoff producing rate, the runoff rate is stable at 182-1200 mL/min after the peak flow rate is reached..Initial runoff-yielding time:Grassland, bare land initial runoff-yielding time shortened with increasing of rainfall intensity and slope. Cynodon dactylon (L.) Pers grass land (which referred to as C land) initial runoff-yielding time from 54’00"(30 mm/h,5°) shortened to 13’30"(90 mm/h,20°) and its bare land from 49’58"(30 mm/h,5°) shortened to 2’18"(90 mm/h,20°); Festuca elata Keng ex E. Alexeev grass land (which referred to as F land) initial runoff-yielding time from 1h24’(30 mm/h、5°) shortened to 20’51"(90 mm/h、20°) and its bare land from 45’24"(30 mm/h、5°) shortened to2’05"(90 mm/h、10°).Peak current time advanced with the increase of rainfall intensity and slope, the maximum was shortened 75 min and shortened 37.5 min averagely. Compared with bare land, grassland has a good delay function, C land averagely need 44 minutes peak current time more than its bare land, F land averagely need 31 minutes peak current time more than its bare land; The delayed effect of grassland on the peak current time was better in the case of smaller rainfall intensity and slow slope.Bare land peak flow under the level of 0.05 was significantly higher than that of grassland; The peak flow of grassland and its bare land increased gradually with the slope and rainfall intensity increased, C land range for 203-750 mL/min and its bare land range for 380-1200 ml/min, F land range for 182-871 ml/min, its bare land range for 361-1070 ml/min.The total runoff volume of the two types of grassland increased significantly with the increase of rainfall intensity and slope. C land total runoff volume from 22.58 L(30 mm/h、 5°)up to 33.77L(90mm/h、20°), the increase rate was 49.56%, while F land from 6.96 L(30 mm/b、5°)up to 30.54 L(90 mm/h、20°), the increase rate was 80.07%; The influence correlation degree of rainfall intensity and slope on the two types of grassland runoff was 0.61、0.60 and0.62、0.51 respectively by the ways of grey relational grade analysis, which means the effect of rainfall intensity on the total volume of grassland was greater than slope.The effect of grassland on runoff reduction was significant; The C land maximum can reduce runoff coefficient 59.02% and averagely reduce 47.54%, F land maximum can reduce runoff coefficient 64.18%and averagely reduce 56.90%; The reduction rate of total runoff is decreased with the increase of rainfall intensity and slope gradient, which decreased as a power function. Runoff reduction rate of C land up to 59.04%(30 mm/h、 5°), the average reduction of total runoff was 47.76%, The maximum runoff reduction rate of F land was 63.41%, minimum was 47.13%. The regression equation about reduction rate and slope and rainfall intensity of two grassland were analyzed, the simulated values of the reduction rates are close to the measured values under this experimental conditions and the absolute error is less than 10%.Nash-Sutcliffe efficiency coefficient of two model equation is 0.69 and 0.18. Cynodon dactylon (Linn.) Pers lawn and Festuca elata Keng ex E. Alexeev lawn can respectively reducing the runoff volume at 47.92%～67.50% and 55.04%-68.16% for 60 minutes on behalf of Station in Beijing between 1941～2010 years.