| With the development of urbanization and the increase of human activities, a large number of natural ground was replaced by the rigid pavement surface, which caused the increasing proportion of impervious surface. In our country, rainwater was regarded as a kind of "waste water" in most cities and adopted the way of “fast row quick-release” to discharge. Even in some developed cities, municipal engineering design, construction and management was still limited in traditional, focusing only on flood control and drainage and with a simple direct platoon. The expansion of the city leads to a series of problems, such as frequent flood disasters, serious water pollution, rainwater resource loss, the shortage of water resources and the ecological environment deterioration. Today, the concept of sustainable development had been widespread into every areas, and how to effectively collect and use rainwater attract more and more people's attention.Based on the concept of “low impact development” and combined with the requirements of the ecological construction of green building, the ladder type green space was improved on the basis of preliminary experiment. Through monitoring the rainfall of the test ground, the article mainly discussed the variation of rainfall runoff pollutant with rainfall duration, the EMC values of runoff pollutants and their correlation, the control effect of the test equipment on runoff pollutants, the volume of runoff reduction and flood peak delay. At the same time, the design calculation method of the improved ladder green under different targets was proposed. The main conclusions were as follows:(1) Based on monitoring the inflow water quality of the test device,which indicated that the pollutant concentration of early stage inlet is highest, and the concentration of SS, COD, TP, TN, NH4+-N, NO3--N were 52.64mg/L~176.91mg/L, 55.72mg/L~152.97 mg/L, 0.30mg/L~1.61mg/L, 0.48mg/L~2.89mg/L and 0.34mg/L~1.27mg/L, 0.16 mg/L~ 0.77mg/L respectively. The pollutant concentration gradually decreased with the extension of duration of rainfall. At the end of the rainfall, the concentration of SS, COD, TP, TN, NH4+-N, NO3--N were 14.18mg/L~47.64mg/L, 10.72mg/L~32.88mg/L, 0.08mg/L~0.33mg/L,0.26mg/L~0.94mg/L,0.11mg/L~0.36mg/L,0.03mg/L~0.16mg/L. Compared with the surface water environmental quality standard(GB3838-2002), NH4+-N can always reach the water standards of grade IV, SS, COD, TP, TN are influenced by the type of rainfall, rainfall intensity, pre drought degree and the concentration range fluctuated greatly. The EMC values of SS, COD, TP, TN, NH4+-N, NO3--N were 28.16 mg/L ~106.37 mg/L?32.40 mg/L ~96.92 mg/L?0.20 mg/L ~0.92 mg/L?0.31 mg/L ~1.24 mg/L?0.20 mg/L ~0.72 mg/L?0.07 mg/L ~0.40 mg/L, which indicated that the diameter water quality generally is lower than that of table water environment class V standards. The correlation analysis showed that COD, TP, TN, NH4+-N, NO3--N and SS had good correlation, which indicated that runoff pollutant mainly existed in the form of particle adsorption.(2) The analysis of overflow and penetration water quality showed that the overflow water of the test device had a certain effect on the removal of COD and SS, but the water quality was generally not satisfied with the standard of the landscape water reuse. The overflow removal of TP and the nitrogen rate was lower. The penetration water quality was better and the concentration of SS, COD, TP, TN, NH4+-N, NO3--N were 6.88mg/L~9.22mg/L, 647mg/L~25.85mg/L, 0.10mg/L~0.24mg/L, 0.16mg/L~0.40mg/L, 0.06mg/L~0.19mg/L, 0.04mg/L~0.21mg/L. The removal rate of each pollutant were 79.4%~91.5%, 69.4%~83.8%, 52.8%~73.2%, 46.1%~68.9%, 50.6%~73.5%, 33.8%~46.8%. The COD of penetration water does not meet the standard of water reuse in landscape when the influent concentration is high. The final concentration of SS, TP, nitrogen can meet "urban wastewater reclamation and reuse of landscape and environmental water quality"(GB/T1981-2002) water quality requirements for ornamental landscape environment.(3) The study on the control effect of runoff amount was as following, the test device for rainfall runoff flood peak has a certain delay. The delay time is between 7min and 17 min. Test device for the rainfall peak reductions is 52.23%~74.51%, which is impacted by the rainfall return period and the prophase rainfall. When the rainfall return period is greater, the peak runoff is larger and the peak flow reduction rate is smaller; when the pre drought degree is higher, the peak flow reduction rate is higher. The test device for reducing the runoff volume reduction rate is from 43.23% to 100%. The reduction of rainfall runoff water and flood peak were influenced by the prophase drought days, heavy rain intensity, the type of the rain. The smaller the rainfall intensity, the longer the sunny days, the more the corresponding water retention.(4) Under different service area and different return periods, the test device can completely dissolve the return period of 0.25 a, service area ratio is 1:3 stormwater runoff. When the return period is 0.33 a, 0.5a, the test device can utilize service area 1:2 stormwater runoff. When the return period of 1a, 2a, 3a, the test device can be completely consumed service area ratio 1:1stormwater runoff.(5) The ladder type green design principles was described from the pre treatment facilities, design objectives, design size and structure of the depth. At the same time, the different target modified type ladder green design method was put forward, and the detailed design of ladder type green calculation method was gaven in the goal of design rainfall, runoff flow volume reduction rate, peak runoff extension rate. In view of the problems existing in the operation of ladder type green space, the matters needing attention during maintenance and management, and the concrete treatment measures and the inspection cycle were put forward.Based on the the study of the step green land controlling the rainfall runoff water showed that step green land has great effect in controlling runoff pollution, time delay of flood peak and cut water, and suggest to expand the scale of the test equipment, monitor the control effect of the water quality and quantity to prepare for the popularization and application. |
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