Hydrologic performance analyses, modeling, and design tool development for green roof systems

Abstract

Green roofs are one of the most recommended best management practices for stormwater management projects. However, their hydrologic performance is difficult to predict or control due to a lack of methodologies for quantitative analyses. The relationship between hydrologic response and its affecting factors, such as green roof configuration, growth media, precipitation properties, antecedent conditions, and evapotranspiration (ET), is highly non-linear. This thesis studied these issues. In this work, more than 100 green roof research papers were investigated and an experimental green roof site with monitoring equipment was constructed. HYDRUS-2D was used for the first time in green roof studies to analyze hydrologic responses of green roofs to ET, irrigation, and precipitation events. Major methodologies developed include: 1) acquiring the growth media hydraulic properties and retention curve parameters; 2) performing dimension simplification to set up simulation geometry; 3) conducting model calibration using growth media water content measurement, precipitation/irrigation monitoring, and ET calculation data; 4) analyzing water content profile for irrigation management; and 5) deriving regression equations for LEED projects. This research also developed a green roof specific model using a system of governing equations. This model resolved the difficulties of general soil physics models in directly connecting hydrologic performance with design parameters, and simulating water storage and extreme dry/wet conditions. It offered rational design-parameter-based criteria for LEED projects. It also discovered the distinctive features of green roof hydrologic response to precipitation characteristics on a broad spectrum through its runoff response curves. Using this model, green roof designs and their hydrologic performance can be iterated to form a powerful design tool for engineers.