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Green roof systems (GRs) provide a promising stormwater management strategy in highly urbanized areas when limited open space is available. Hydrological modeling can predict the ability of GRs to reduce runoff. This paper reviews three popular types of GR models with varying complexities, including water balance models, the U.S. EPA's Stormwater Management Model (SWMM), and Hydrus-1D. Developments and practical applications of these models are discussed, by detailing model parameter estimates, performance evaluations and application scopes. These three models are capable of replicating GR outflow. Water balance models have the smallest number of parameters (≤7) to estimate. Hydrus-1D requires substantial parameterization effort for soil hydraulic properties but can simulate unsaturated soil water flow processes. Although SWMM has a large number of parameters (>10), it can simulate water transport through the entire GR profile. In addition, SWMM GR models can be easily incorporated into SWMM's stormwater model framework, so it is widely used to simulate the watershed-scale effects of GR implementations. Four research gaps limiting GR model applications are identified and discussed: drainage mat flow simulations, soil characterization, evapotranspiration estimates, and scale effects of GRs. The literature documents promising results in GR simulations for rainfall events, however, a critical need remains for long-term monitoring and modeling of full-scale GR systems to allow interpretation of both internal (substrate) and external (meteorological characteristics) system effects on stormwater management.
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Assessment of the long-term hydrological performance of a green roof system in stormwater control
Green roof systems (GRs) are effective tools for urban stormwater management. However, there is limited documentation of the long-term hydrological performance of GRs to support decision-making. This study evaluated long-term field monitoring records (7 years) from a 12-year-old GR, situated in a Moist Subtropical Mid- Latitude Climate, to analyze seasonality in and evolution of hydrological performance. The monitoring system was built within a pan lysimeter buried under substrate layers matching the surrounding GR. The monitoring results highlight the efficacy of this GR in long-term stormwater runoff control. The GR can retain 87% of the annual precipitation and return 54% of the precipitation to the atmosphere through evapotranspiration (ET) and sustain long-term event-based mean runoff volume reductions, peak flow reductions, and flow delays of 82%, 93%, and 4.3 h, respectively. The initial moisture content prior to events was highly correlated with hydrological performance, with a seasonal mean Spearman correlation coefficient of 0.47, suggesting the potential of enhancing ET from the GR to improve performance. Substrate water holding capacity increased over time, but no obvious changes in water retention performance were observed. These monitoring results from the aging GR demonstrate the effectiveness of GR systems for long-term stormwater management.
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- Award ID(s):
- 1854827
- PAR ID:
- 10660970
- Publisher / Repository:
- Elsevier
- Date Published:
- Journal Name:
- Journal of Environmental Management
- Volume:
- 370
- Issue:
- C
- ISSN:
- 0301-4797
- Page Range / eLocation ID:
- 122831
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
-
Accepted Manuscript
- Journal Article:
- https://doi.org/10.1016/j.jenvman.2024.122831
