| Recently the government of Shanghai city promotes the construction of green roofs, especially after the 2010 World Expo in Shanghai which had made great progress on the green roof technologies. At present, the related researches on green roof mainly focused on its applicability, construction technologies, and comprehensive evaluation systems for qualitative research, plant selection and maintenance. The existing researches showed that the matrix layer of green roofs could store and purify rainwater to some extent. While, the effects of the extensive green roof media on rainwater detention and purification have not been adequately quantified in Shanghai district. In this thesis, based on the present situation of green roofs and characteristics of atmospheric precipitation in Shanghai, the influences of extensive green roof matrix layer on stormwater retention and purification were quantitatively analyzed in Shanghai to optimize the thickness and compositions of substrate and water retention agent(sodium polyacrylate) dosage for extensive green roof construction through orthogonal test. The results were as followed:(1) The extensive green roof in Shanghai could remarkably detent the stormwater. Rainwater was totally kept in green roof when the rainfall intensity was less than 5mm/12 h. While rainwater detention storage reached 63.54% even in the case of heavy rain which was 49mm/12 h. The initial runoff could be retarded up to 34 min.(2) The stormwater could be remarkably purified by the extensive green roof. In case of heavy rain, up to 92.78% of ammonia in stormwater was removed by the expand green roof stormwater. The average concentration of ammonia in runoff was reduced to 0.45 mg/L which was far below 5 mg/L, the average concentration in rain, and better than the class II standard of surface water. Pb in stormwater was removed as high as 98.81%. The runoff reached the surface water class I standard, far lower than the average concentration of 260 μg/L. As high as 94.55% Zn was removed from the stormwater. Zn in runoff was reduced to the average concentration of 0.02 μg/L, reached the surface water class I standard, far better than the rain the average concentration of 60 μg/L.(3) The effect of media depth on stormwater retention of extensive green roof in Shanghai was the greatest among those of the three factors. As the media depth was 300 mm, the average stormwater detention and retention rate reached 57.52%, and average initial runoff yielding time was postponed 80 min. The effect of sodium polyacrylate on stormwater retention of extensive green roof in Shanghai was just after that of media depth. As the sodium polyacrylate was 4 g/L, the effect of stormwater detention was the best among the three levels of sodium polyacrylate and average postponed initial runoff yielding time was the longest. The media proportion had the minimal effect on stormwater retention of extensive green roof in Shanghai. As the media proportion of loam: perlite: cocopeat was 1:1:2, the effect on stormwater retention was the greatest. As the media proportion of loam: perlite: cocopeat was 1:2:1, the average delayed initial runoff yielding time was the longest.(4) The effect of media depth on stormwater purification of extensive green roof in Shanghai was the greatest among those of the three factors. As the media depth was 300 mm, the effect on stormwater purification was the best, and 91.19% NH4+, 98.81% Pb and 94.55% Zn were removed. The effect of sodium polyacrylate on stormwater purification was after that of media depth. As the sodium polyacrylate was 4 g /L, the effect on purification of Pb was the best. As the sodium polyacrylate was 2 g/L, the effect on purification of NH4+ and Zn were the best. The media proportion had the minimal effect on stormwater purification. As the media proportion of loam: perlite: cocopeat was 1:1:2, the effect on purification of NH4+ was greatest. As the media proportion of loam: perlite: cocopeat was 1:2:1, the effect on purification of Pb and Zn were greatest. |
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