The Influence of Hydrologic Parameters on the Hydraulic Efficiency of an Extensive Green Roof in Mediterranean Area

Giuseppina Garofalo,Francesca Principato,Stefania Palermo,Patrizia Piro,Theodoros Theodosiou

doi:10.3390/w8020044

Giuseppina Garofalo, Francesca Principato + Show 3 more

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https://doi.org/10.3390/w8020044

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Abstract

In an urban environment, green roofs represent a sustainable solution for mitigating stormwater volumes and hydrograph peaks. So far, many literature studies have investigated the hydraulic efficiency and the subsurface runoff coefficient of green roofs, showing their strong variability according to several factors, including the characteristics of storm events. Furthermore, only few studies have focused on the hydraulic efficiency of green roofs under Mediterranean climate conditions and defined the influencing hydrological parameters on the subsurface runoff coefficient. Nevertheless, for designing purposes, it is crucial to properly assess the subsurface runoff coefficient of a given green roof under specific climate conditions and its influencing factors. This study intends to, firstly, evaluate the subsurface runoff coefficient at daily and event-time scales for a given green roof, through a conceptual model implemented in SWMM. The model was loaded with both daily and 1-min rainfall data from two Mediterranean climate sites, one in Thessaloniki, Greece and one in Cosenza, Italy, respectively. Then, the most influencing hydrological parameters were examined through a statistical regression analysis. The findings show that the daily subsurface runoff coefficient is 0.70 for both sites, while the event-based one is 0.79 with a standard deviation of 0.23 for the site in Cosenza, Italy. The multiple linear regression analysis revealed that the influencing parameters are the rainfall intensity and antecedent dry weather period with a confidence level of 95%. This study demonstrated that, due to the high variability of the subsurface runoff coefficient, the use of a unique value for design purposes is inappropriate and that a preliminary estimation could be obtained as a function of the total rainfall depth and the antecedent dry weather period by using the validated multi-regression relationship which is site specific.

Highlights

In an urban environment, the ongoing surface sealing due to the development of built-up areas and motorways have produced a constant loss of natural areas
The results showed that for small rainfall events, the green roof was able to reduce the stormwater through the interception by the plants, while for the higher events there was an increasing runoff in the substrate, caused by the preferential flux paths generated by the root apparatus
The conceptual model, described was built and validated with the measured data retrieved from an experimental green roof located at the University of Calabria, Italy

Summary

Introduction

The ongoing surface sealing due to the development of built-up areas and motorways have produced a constant loss of natural areas. The drastic changes in the natural hydrological cycle, such as the reduction of infiltration and evapotranspiration, have increased the runoff volumes. During extreme rain events such volumes can overload urban drainage systems and cause local floods [1,2]. To restore the pre-development hydrologic cycle, green roofs can be implemented in urban areas. Such systems are structural facilities which are to capture, infiltrate, evaporate, and in combination. Green roofs promote evaporative cooling, thereby offsetting the energy requirements associated with air conditioning systems and reducing urban heat island effects [6,7]

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