A guide to assessing green infrastructure costs and benefits for flood reduction

The purpose of this guide is to provide a process that communities can use to assess the costs and benefits of green infrastructure to reduce flooding. The guide takes a step-by-step, watershedbased approach to documenting the costs of flooding; projecting increased flooding and associated costs under future land use and climate conditions; and calculating benefits and costs of reducing flooding with green infrastructure over the long term. The guide is based on the experiences of three communities in the Great Lakes region (Duluth, Minnesota; Toledo, Ohio; and Green Bay, Wisconsin). To ensure transferability to different types of watersheds and communities, the methods were applied to the He‘eia watershed in Hawai‘i. Valuable transferability insights from the He‘eia watershed partners have been incorporated.

Communities should use this guide as a framework that can be adapted for their own purposes to inform planning-scale assessments and spark discussion about green infrastructure options to mitigate flooding and provide other watershed benefits. By following the guide’s six steps for developing a green infrastructure strategy, including estimation of associated costs and benefits over a chosen planning horizon, communities can demonstrate the cost-effectiveness of implementing green infrastructure projects. This guide does not compare costs between traditional gray and green infrastructure. It should also be noted that there is always a level of uncertainty associated with the use of models and future flooding predictions; the models and predictive tools used here are intended for planning-scale levels of effort. More detailed analyses are recommended for site-specific green infrastructure design.