Study On Rainwater Retention Effect And Pollutant Leaching Characteristics Of Green Roof

In order to quantitatively evaluate the differences of rainwater retention effect and pollutant leaching of green roof facilities with improved soil matrix structure in China,nine green roof model devices(No.GR1-GR7)with length,width and height of 1m ×1m × 0.15 m were constructed.The four indexes of rainwater retention efficiency,retention time,peak lag time and peak discharge reduction,as well as the changes of total nitrogen,nitrate nitrogen,nitrite nitrogen,ammonia nitrogen,total phosphorus,COD and turbidity in each unit were measured by means of the combination of indoor simulated rainfall and outdoor natural rainfall monitoring.The results of research show that: GR1 has excellent rainwater retention time and peak lag time capacity,and good effluent water quality,and does not have high pollutant leaching risk.However,due to the lack of nutrients,plant growth is poor.GR2 and GR3 have better rainwater retention capacity,but their early outflow has higher concentration of nitrogen,phosphorus and COD leaching risk.GR4 and GR5 also have better rainwater retention capacity in general,and the discharge nitrogen and phosphorus pollutant concentrations are low.GR6 not only has poor rainwater retention capacity,but also has high leaching risk of nitrogen,phosphorus and COD.GR7 may have poor plant growth in the early stage due to the addition proportion of biological organic fertilizer in the improved soil,but it tends to get better in the later stage as the experiment goes on.Research results indicate that it is not comprehensive to evaluate the rainwater regulation performance of green roof facilities only from a single index such as rainwater retention effect or pollutant emission characteristics.Some green roofs have better rainwater retention effect,but there may be serious pollutant leakage problem(GR2,GR3).Some green roofs have the advantage of low pollutant concentration,but they also have disadvantages such as backward plant growth and development and insufficient rainwater retention capacity(GR1).The main reason for the contradiction is that the proportion of nutrients added in the improved soil is not appropriate.The method of comprehensively evaluating the rainwater regulation performance of green roofs based on model tests should be the first to apply green roof facilities on a large scale,so as to avoid the non-point source pollution problems that may be brought by green roofs and maximize the advantages of rainwater runoff regulation in the region.