Vegetated Infrastructure for Urban Stormwater Management: Advances in Understanding, Modeling and Design

There are many documented environmental benefits to concentrating populations in cities. However, the impermeable nature of modern urban landscapes, which has been created by roads, buildings, and paved public spaces, has altered the natural cycle of water through today’s cities. As a result, a greater fraction of rainfall becomes runoff, creating stormwater pollution that degrades the very host environments needed to support city living. One attractive approach to urban stormwater management is the use of engineered and non-engineered vegetative systems to reduce the amount of rainfall that becomes runoff. When one considers the vast number of vegetative systems needed to bring about significant change, along with the variety of environmental niches in the urban landscape, it is clear that an array of “greening” strategies are needed. In turn, accurate performance data and models of these strategies are necessary to appropriately inform design and policy decisions. The research presented in this dissertation focuses on advancing the understanding, modeling, and design of three types of vegetated infrastructure with potential to address urban stormwater challenges: extensive green roofs, street trees, and vine canopies. The first research focus examines a nuance to a well-developed and well-studied technology: the extensive green roof. Nearly four years of environmental and runoff monitoring data from two full-scale extensive green roofs are used to determine how the time of year impacts hydrologic performance while considering the covariates of antecedent dry weather period, potential evapotranspiration and storm event size. Comparisons are made between thick and thin extensive green roof systems, and novel models are presented which account for seasonal variability. The second research focus evaluates the absorptive capacity of an existing type of urban vegetation: the street tree. In particular, this work looks at the permeability and infiltration capacity of the tree pit’s soil surface, which is often a controlling factor in the hydrologic performance of street trees. The resulting model links physical features of the tree pit to its ability to absorb water. Furthermore, the results indicate two simple, low-cost management strategies to improve urban stormwater capture via street trees. The third research focus explores the stormwater management potential for a new type of vegetated infrastructure: the horizontal vine canopy. Hydrologic performance data from sixteen vine canopies grown on a New York City rooftop are used to determine the capacity of the vines to retain stormwater, return water to the atmosphere via transpiration, and grow in the harsh rooftop conditions. Models and coefficients describing stormwater capture and plant transpiration are then presented and used to estimate the potential capacity of vine canopies to contribute to urban stormwater management. Exploration into new forms of vegetated infrastructure and facets of existing urban vegetation through the perspective of stormwater management has resulted in valuable findings and experimental methodologies. In several instances, these studies required new measuring equipment or sampling procedures, which were developed, validated, and made available for future research