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Developing an integrated planning-level approach for optimizing green to grey stormwater management solutions
Gallo, Elizabeth Marie
Gallo, Elizabeth Marie
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2020
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Urbanization is expected to persist in cities across the world, resulting in increased percent imperviousness, alterations to the hydrologic regime, degraded water quality, and deteriorated ecosystems. Stormwater Control Measures (SCMs) have been developed to mitigate some of the impacts of urban development, but come in a wide range of designs and have variable hydrologic performance based on their primary function. SCMs exist on a continuum that ranges from green (typically above ground infrastructure that includes vegetation) to grey (large storage facilities or underground distributed infrastructure). The decision-making process for an optimal stormwater management plan on a watershed-scale is complex and multi-faceted. Conflicting stakeholder interests need to be considered when determining the optimal suite of SCMs for a particular watershed. Hydrologic models, such as the EPA’s System for Urban Stormwater Treatment and Analysis INtegration (SUSTAIN) can be used to simulate water quantity and quality as well as evaluate the implementation of SCMs on a watershed-scale. Decision support tools can assist stakeholders and decision makers in optimizing between varying SCM types based on the needs and priorities of their specific watershed and communities. The research in this dissertation uses a hydrologic model and decision support tool and aims to improve stormwater modeling by 1) exploring the feasibility of meeting regulatory compliance with the implementation of SCMs, 2) investigating the performance and tradeoff of greener to greyer SCMs using optimizations, and 3) improving the decision-making process by incorporating life cycle costs and a benefit analysis with stormwater modeling. A multi-watershed analysis conducted in Los Angeles County found that meeting water quality regulations when implementing SCMs on a watershed-scale is dependent on percent imperviousness and land use characteristics which impact baseline water quantity and quality. Despite routing runoff from 90% of the watershed to greener SCMs only three of the six simulated SCM solutions reached compliance in the Ballona Creek watershed and none were successful in the Dominguez Channel and Los Angeles River watersheds, highlighting the need for a more robust planning-level approach to determine the optimal stormwater management plan. The investigation of greener vs greyer SCMs in the Berkeley Lake neighborhood, (Denver, CO) found that all SCM types offer varying hydrologic benefits based on their design and function. For example, underground infiltration (greyer) and infiltration trenches (greener) are optimal for reducing average annual flow volume while underground detention (greyer) and vegetated swales (greener) are better at reducing pollutant average annual concentrations. Optimizing (maximizing a benefit and minimizing cost) between thousands of SCM solutions and rating benefits based on stakeholder preferences identified that while the primary goal of a watershed may initially put more weight on particular SCM types, the consideration of multiple benefits exposes which additional SCMs should be included in order to maximize the benefits of a watershed. A comparison between capital and life cycle costs (LCC) for SCM types identified two differences which significantly impact optimal solutions, cost magnitude and cost order. LCC were found to be millions to billions of dollars higher than capital costs and shifted the relative cost order of SCMs in a watershed (lowest to highest). Finally the use of varying management criteria, classified by hydrologic and vegetative benefits and specific to the respective watershed, determined that while a hybrid solution (green and grey SCMs) is optimal for more stakeholders in Ballona Creek watershed (Los Angeles, CA) a greener solution is optimal in the Berkeley neighborhood watershed (Denver, CO).
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