An ASCE-Inspired investigation of the model-dependent stormwater management benefits of retrofitted extended tree pits in Hamilton, ON

Robert Rawlins and Yiping Guo


The UN’s Sustainable Development Goals (SDGs) and the IPCC’s 1.5°C report are reminders of the work required to prevent seemingly inevitable catastrophe and establish a sustainable world (IPCC 2018; Annan 2017). Understanding the profession’s unique obligation in sustainable development, the American Society of Civil Engineers’ (ASCE) 5-year plan to Sustainable Development outlines four keys to realizing the profession overhaul centred on resourcefulness, resilience, integration, collaboration, nature based solutions, and advocacy (ASCE 2018). In the context of stormwater management (SWM), decades of expert publications point to Green Infrastructure (GI) and nature-based Low Impact Development (LID) implementation as key to establishing sustainable urban drainage systems (SUDS) (Yazdanfar and Sharma 2015; Ahiablame and Shakya 2016; Marlow et al. 2013; Pumo et al. 2017; Dong, Guo, and Zeng 2017). In urban environments, extensive research highlights street trees and extended tree pits (ETPs) as simultaneously offering runoff volume and pollution control as well as various other ecoservices, while also highlighting optimal sizing and design criteria (Gillner et al. 2015; Silvera Seamans 2013; Grey et al. 2018; Collentine and Futter 2018; Xiao and McPherson 2002; Grey 2018; McGarity et al. 2015). Following the ASCE’s advice to broaden the scope of projects and use what’s available to create needs-based solutions, this project used the extensive research on street trees for stormwater management, the abundance of GIS data, and several of the various deterministic (PCSWMM, i-Tree, National Stormwater Control (SWC), GIFMod, and LID TTT) and probabilistic ((Zhang and Guo 2013)) models available to explore the benefits of retrofitting ETPs to already-established street trees in Hamilton’s Beasley and Landsdale neighbourhoods.

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