This guide provides a process that communities can use to assess the costs and benefits of green infrastructure to reduce flooding. The framework 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.

Following a step-by-step, watershed-based approach, the document guides users through 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.

Drawing from four case studies (Duluth, Minnesota; Toledo, Ohio; Green Bay, Wisconsin; and He‘eia, Hawaii), the guide provides key considerations, recommended expertise, practical implementation tips, and lessons learned. The document outlines a six-step process, with specific tasks associated with each step:

• Define the flooding problem
• Assess flooding scenarios without green infrastructure
• Identify how a flood reduction target can be met with green infrastructure
• Assess flooding scenarios with green infrastructure
• Estimate benefits and costs
• Identify and communicate the desired green infrastructure strategy

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.

The 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 are intended for planning-scale levels of effort. More detailed analyses are recommended for site-specific green infrastructure design.