| Extreme rainfall events are becoming more and more frequent under the background of global warming.However,the rapid urbanization process leading to inadequate construction of urban drainage system which gave rise to serious urban flooding.In order to alleviate the disaster caused by rain,many solutions have been put forward at home and abroad.Green roofs are highly regarded as one of the ways of runoff controlling.Based on the experience of green roof construction,a new type of green roof(container green roof)is proposed.This type of green roof adopts light container to replace the waterproof layer of conventional green roof,which has certain innovation and breakthrough.Based on the influencing factors of green roof runoff,the green roof system is constructed in this paper.The influence of substrate type,substrate thickness and rainfall intensity on roof runoff was discussed by controlling experiment.This paper discusses the correlation between the thickness of water storage layer and the thickness of substrate and the water holding capacity of green roof.Relevant conclusions are as follows:(1)Different substrate types have different processing capacities for runoff.Through the experimental comparison between silicate mixed matrix(peat soil: pumice =3:1)and high-temperature combustion oxide mixed matrix(peat soil: slag =3:1),it was found that when the rainfall intensity was 0.3mm /min and the substrate thickness was 300 mm,the runoff formation time of silicate mixed matrix was 255 min and the runoff peak arrival time was 310 min.In addition,the formation time(230 min)of high-temperature combustion oxide mixture matrix was delayed by 9.8%,and the arrival time of peak runoff(280 min)was delayed by 9.6%.Silicate mixture matrix was more suitable for green roof runoff treatment than high-temperature combustion oxide mixture matrix.(2)Based on the rainfall characteristics of rainfall simulation experiments in Shanghai,the relationship between subtrate thickness and runoff formation time was explored.It is found that the thickness of substrate is non-linearly related to runoff formation.Considering the load requirements and cost of green roof construction,the optimal substrate thickness for container green roof construction was determined to be 300 mm.(3)There was a negative correlation between rainfall intensity and runoff formation time.When the experimental rainfall intensity was 0.3-0.9mm /min,the runoff formation time was about 140-230 min.When the experimental rainfall intensity was between 1.05 mm/min and1.35 mm/min,the runoff formation time was sharply shortened.Even that the runoff retardation effect was not obvious.(4)Through the determination of Volume Moisture Content(VWC)of green roof,it can be concluded from the experiment that the moisture holding capacity of green roof depends on the water storage layer and matrix layer,and the thicker the water storage layer and matrix layer of green roof,the stronger the Moisture holding capacity of green roof.(5)the Preliminary Hazard Analysis(PHA)was applied to evaluate the safety and stability of the green roof embodiment in jinkai municipal administration of Shanghai.Through continuous observation,the runoff treatment capacity of green roof and the drought resistance of inter-rain period were compared and evaluated.It is proved that container green roof has better resistance and tolerance than conventional green roof under natural conditions. |
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