Hydrologic Performance of Experimental Green Roofs Stands as the Effect of Climate Condition

The water storage capacity of a green roof forms several benefits for the building and its environment. The hydrologic performance is traditionally expressed by the runou coefficient, according to international guidelines and standards. The runoff coefficient is a dimensionless coefficient relating the amount of runoff to the amount of precipitation received. It is a larger value for areas with low infiltration and high runoff (pavement, steep gradient), and lower for permeable, well vegetated areas (forest, flat land). The paper is presenting 3 experimental stands of green roofs. Each stand is unique in terms of its construction. The aim of this paper is to highlight how green roof responds to real clima events. The experiment provides mathematical graphs and behaviour of the geen roof stands from 03/2019 to 01/2021.

Development and Application of a SWMM-Based Simulation Model for Municipal Scale Hydrologic Assessments

There is growing interest for the installation of green stormwater infrastructure (GSI) to improve stormwater control, increase infiltration of stormwater, and improve receiving water body quality. Planning level tools are needed to inform municipal scale decisions on the type and extent of GSI to apply. Here, a modified methodology is developed for the EPA Storm Water Management Model (SWMM) to create SWMM for Low Impact Technology Evaluation (SWWM-LITE) that enables municipal scale assessment of stormwater control measure (SCM) performance with minimal input data requirements and low processing time. Hydrologic outputs of SWMM-LITE are compared to those for SWMM and the National Stormwater Calculator (SWC) to assess the performance of SWMM-LITE. Three scenarios including the baseline without SCMs and the installation of varying SCMs were investigated. Across the three scenarios, SWMM-LITE estimates of annual average hydrologic performance (runoff, infiltration, and evaporation) were within +/−0.1% of estimates from a rigorously developed SWMM model in the City of Fort Collins, CO, for an evaluation of 30 years of continuous simulation. Analysis conducted for 2 year (y), 10 y, and 100 y storm events showed less than +/−2.5% difference between SWMM and SWMM-LITE hydrologic outputs. SWC provided reasonable estimates of hydrologic parameters for the case study area, but was designed for site level analyses of performance of SCMs rather than on the municipal scale. A sensitivity analysis revealed that the most sensitive parameters were primarily consistent for the SWMM-LITE and the complete SWMM. SWMM-LITE has low input data requirements and processing time and can be applied for assessing the hydrologic performance of SCMs to inform planning level decisions.

Hydrologic Performance of an Extensive Green Roof under Intensive Rain Events: Results from a Rain-Chamber Simulation

The water storage capacity of a green roof generates several benefits for the building conterminous environment. The hydrologic performance is conventionally expressed by the runoff coefficient, according to international standards and guidelines. The runoff coefficient is a dimensionless number and defines the water retention performance over a long period. At the scale of single rain events, characterized by varying intensity and duration, the reaction of the green roof is scarcely investigated. The purpose of this study is to highlight how an extensive green roof—having a supposed minimum water performance, compared to an intensive one—responds to real and repetitive rain events, simulated in a rain chamber with controlled rain and runoff data. The experiment provides, through cumulative curve graphs, the behavior of the green roof sample during four rainy days. The simulated rain events are based on a statistical study (summarized in the paper) of 25 years of rain data for a specific location in North Italy characterized by an average rain/year of 1100 mm. The results prove the active response of the substrate, although thin and mineral, and quick draining, in terms of water retention and detention during intense rain events. The study raises questions about how to better express the water performance of green roofs.

Hydrologic Performance of an Extensive Green Roof in Syracuse, NY

Green roof performance reported in literature varies widely—the result of differences in green roof design and climate, as well as limitations in study design and duration. The need exists for full-scale studies under real climate conditions to inform the design, modeling, and planning of new green roof installations. The purpose of this study is to quantify hydrologic performance of a large green roof and characterize its dominant physical processes. To achieve this, a 5550 m2 extensive green roof in Syracuse, New York, designed to hold a 25.4 mm rain event, is monitored for 21 months. Over the monitoring period, the roof retains 56% of the 1062 mm of rainfall recorded. Peak runoff is reduced by an average of 65%. Eleven events exceed 20 mm and are responsible for 38% of the rainfall and 24% of the annual retention. Retention in the summer is lower than that in the fall or spring, as a result of greater rainfall intensity during the period sampled. Soil moisture during winter months remains high, reducing the ability of the roof to retain rainfall volume from new events. Comparison of seasonal data demonstrates the strong influence of rainfall intensity on runoff and the effect of initial soil moisture on event retention.