Triple Bottom Line Cost-benefit Analysis of Green Infrastruct ...


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Green infrastructure (GI) has become a promising practice in reducing flood risks and improving water quality in urban and suburban areas by decreasing stormwater runoff volume and peak flow, while limiting terrestrial-to-aquatic nutrient flows. In addition, GI provides a broad range of secondary ecosystem services, such as urban temperature amelioration and scenic beauty. Yet, individual web-accessible calculators often exclude many of these broader inputs and services. To identify economically viable alternatives, acquire stakeholders’ support, and alleviate public concerns, a broader approach to cost-benefit analysis for GI is necessary and may be required by future federal and local regulations. As a result, a triple bottom line cost-benefit analysis model was used to evaluate the sustainability of a recently completed GI project entitled Trailwoods Greenstreet in Norman, Oklahoma, over a thirty year period. Green infrastructure practices of rain gardens, rain barrels, pervious pavements, and trees were installed in the Trailwoods Greenstreet project on thirty-five residential lots to improve the water quality of nearby Lake Thunderbird. In addition, the financial, environmental, and social benefits of green infrastructures in this project were assessed using the model proposed. The thirty-year life-cycle cost was found to be $208,332 and the benefit was found to be at least $2,135,430. Therefore the life-cycle minimum savings of $1,927,098 contrasts favorably to the life-cycle loss of $89,193 that would be associated with conventional stormwater infrastructure. The model was further explained and discussed regarding its relevance and limitations to wider GI cost-benefit analysis.