Experimental Study on the Retention and Interception Effect of an Extensive Green Roof (GR) with a Substrate Layer Modified with Kaolin

Chen Xu,Zaohong Liu,Guanjun Cai,Jian Zhan

doi:10.3390/w12082151

Abstract

Extensive green roofs (GRs) often appear as pollution sources during actual rainfall events; therefore, it is necessary to study the control of nutrient leaching in the substrate layer. In this study, four extensive GR experimental devices are built: two with artificial granular structure substrate layers improved with kaolin as a binder, one with a commercial substrate layer, and one with a standard roof (SR). Based on the simulated rainfall conditions in different local recurrence periods, the delayed outflow time, rainfall retention rate, event mean concentration (EMC), and cumulative pollutant quality of NH4+, NO3−, NO2−, and PO43− in the effluents were measured and evaluated. The results of the study indicate that under simulated rainfall in all the experimental design recurrence periods, the kaolin-modified substrate layer does not exhibit a more significant retention capacity than the commercial substrate. However, it does show some suppression of the leaching effect of NO3− and PO43− in the runoff. The reduction rate of cumulative NO3− quality is 6.56%, and PO43− is 10.54%. In future practical engineering and related research, attention should be paid to the influence of the type and addition amount of the substrate layer modifier on the stability of the granular structure to prevent nutrient loss caused by soil erosion.

Highlights

With the rapid development of global urbanization, the hardening rate of underlying urban areas has increased, leading to frequent cases of urban waterlogging and non-point source pollution
GR3 shows a stronger ability to intercept NO3−. This shows that the artificial granular structure made with kaolin has some ability to control nutrient leaching from the green roofs (GRs) substrate layer; this agrees with the results reported by Zhang
(3) Future relevant research should focus on the effect of the type and amount of addition of the substrate layer modifier on the stability of the granular structure on the interception effect of rainfall runoff

Summary

Introduction

With the rapid development of global urbanization, the hardening rate of underlying urban areas has increased, leading to frequent cases of urban waterlogging and non-point source pollution. As one of the important low-impact development measures, green roofs (GRs) can effectively address the problem of rainwater management as long as they make full use of the existing roof space, which has generated extensive research by domestic and foreign experts [1,2,3,4,5]. Shafique et al evaluated the performance of GRs in highly urbanized areas of Seoul, South Korea [6]. The results showed that GRs could reduce runoff by 10% to 60% under different rainfall intensities. Gao et al used MATLAB to develop the Illinois urban hydrologic model-green roof (IUHM-GR) combination model [7]. The simulation results showed that GRs have a good effect on rainwater retention and could effectively reduce the total amount and peak value of rainwater runoff. Dimitar et al experimentally showed that PH, TP, NO3 − , and Cl− in the effluent quality of GRs were better than that of impervious surfaces [8]

Methods

Results

Conclusion