Executive Summary

As we struggle to deal with the pressing challenges of urbanization, climate change, and resource scarcity, cities of all sizes are looking for innovative solutions that solve myriad issues, from flooding to stormwater compliance and water quality issues. Blue-green infrastructure alternatives have emerged as powerful approaches that integrate natural elements with engineered systems, and they often offer overlapping benefits. However, integrating these techniques effectively can prove challenging.

The Blue-Green Infrastructure & Innovation (BGI•2) Framework is a tool designed by SIG to evaluate green/blue infrastructure alternatives that deliver intended outcomes unique to your community. The BGI•2 Framework combines urban planning, water management, green space, and ecological design to enhance urban livability, mitigate climate risk, and promote human and environmental health. In addition, it utilizes innovative technologies to address issues like affordability, maintenance, and long-term system performance.

Introduction

The BGI•2 Framework is a tool designed to evaluate green/blue infrastructure alternatives that deliver intended outcomes unique to your community.

Step 1—Prioritization

The first step in the framework is to prioritize key outputs of the program. Understanding how/whether each of the main factors influenced by BGI programs — including compliance requirements, flood mitigation, protection of life & property, heat island mitigation, water quality improvement, air quality improvement, and quality of life—fits within your community’s strategic objectives is a critical first step to building a program that meets your needs.

Step 2—Placement

Once the priorities have been identified, Step 2 is to conduct a series of analyses evaluating where within your community BGI will have the greatest impact across multiple stakeholders. Considerations include ecosystem impacts, benefits to downstream or adjoining waterbodies, and leveraging existing environmental and infrastructure features. The assessment culminates in a mapped decision matrix that identifies locations with overlapping benefits and ROIs of each initiative.

Step 3—Design & Delivery

Step 3 is to design and outline your BGI approach, including location, scope, budget, timeline, anticipated benefits, and KPIs. Delivering on the plan requires funding, resources, and procurement, as well as implementation. Simply put, it’s design, build, and build.

Step 4—Impacts & ROI

The fourth and final step is to demonstrate—and document—both the immediate and long-term benefits of your properly managed BGI program. Doing so successfully leads to increased resource allocation and additional grant funding for expansion.

Implementing the BGI•2 Framework requires a collaborative effort involving multiple stakeholders, including city government, urban planners, engineers, scientists, community representatives, and residents. The Framework defined herein simplifies the planning and assessment approach, allowing you to identify suitable locations and the most appropriate technologies, as well as to integrate them into your community for the greatest impact. Ongoing monitoring, evaluation, and adaptive management ensure the program’s long-term success by providing you with the insights you need to optimize its outcomes.

When all these factors are wholly integrated, the pathway to achieving community priorities become easy to execute, and the benefits are immediate

Step 1: Prioritization

By incorporating BGI into city initiatives, municipalities can address multiple urban challenges simultaneously, which enhances community resilience, protects human health and the environment, and mitigates climate risk. While the Framework approach is the same across communities, the priorities and outcomes can be very different. Common priorities targeted by BGI initiatives are: ­

  • Every one of these benefits leads to improvement/protection of life and property.
  • The specifics of each of these factors are unique to each community.

Compliance & Water Quality

Rain gardens, green roofs, permeable pavements, and bioswales capture, retain, and absorb rainfall and runoff, which improves water quality by reducing the volume and velocity of runoff, filtering pollutants, and replenishing groundwater resources. As a result, blue-green infrastructure systems remove contaminants and improve the quality of stormwater before it reaches water bodies, ensuring compliance with stormwater regulations and enhancing overall water resource management.

Flood Mitigation

BGI reduces the burden on conventional drainage systems, which mitigates the risk of flooding, backups, and overflows. It helps manage increased precipitation and storm events, reduces the risk of urban flooding, protects coastal areas from erosion and sea-level rise, and enhances overall urban resilience in the face of changing climate patterns.

Heat Island Mitigation

While historically overlooked as a benefit, heat island mitigation is an incredible benefit of green roofs, urban forests, and greenspace. These features provide shade and offer cooling through evapotranspiration, and they reduce ambient temperatures. In turn, energy consumption costs drop, and health risks associated with extreme heat are reduced.

Air Quality Improvements

Air quality is another BGI benefit that is often overlooked. The plants act as natural air filters, reducing air pollution by capturing particulate matter and absorbing harmful gases. Green walls, street trees, and vegetated buffers along roads and industrial areas help mitigate the impacts of vehicle emissions and industrial pollution, leading to improved air quality and public health.

Recreation & Aesthetics

Access to green spaces and nature has positive impacts on community well-being, mental health, and quality of life. Community gardens, pocket parks, and urban forests provide recreational opportunities, promote social interaction, and enhance overall livability, contributing to more equitable, healthful, and inclusive urban environments.

Step 2: Placement

Now that you have the issues identified and prioritized, you need to conduct an objective analysis of community-specific data that allows us to identify areas of greatest impact and highest ROI once BGI is implemented. Proper placement and design are essential for maximizing the effectiveness of BGI and for ensuring optimal functionality. By strategically locating BGI elements such as rain gardens, bioswales, green roofs, and urban forests, you maximize their benefits and tailor them to address specific challenges.

Proper placement considers factors such as topography, hydrological patterns, land use, and existing infrastructure. Identifying areas prone to flooding, heat island effects, and/or water quality impacts enable BGI to act as natural buffers, intercepting and treating stormwater runoff, reducing pollutant loading, providing shade and cooling, and enhancing ecological connectivity.

Methodology

In many ways, understanding absolutely everything about the physical environment in which you operate helps determine what BGI initiatives are most appropriate where. However, we utilize a simplified approach for urban BGI design that incorporates the following data layers by census tract and parcel to incorporate economic benefit:

  • Zoning and land use
  • Population density
  • Impervious surfaces
  • Land cover (developed vs. natural/water)
  • Soil type (namely bedrock or clay)
  • Risk (flood, heat, and social equity)

Output

Weighting and consolidating the datasets into a single layer identifies candidate areas for installation, the type of BGI initiative that will be most effective (aboveground retention/detention, belowground retention/detention, gray infrastructure, or ecosystem restoration), and the mitigation impact (flooding, heat islands, or air or water quality).

As you complete the mapping and analysis, you can then identify and prioritize a series of suitable BGI initiatives for your community. Oftentimes it is of value to consider and integrate a range of alternatives, including rain gardens, bioswales, green roofs, street trees, permeable pavements, and vegetated buffers.

Determine the ROI for each of the initiatives based on the candidate areas identified above.

Key steps involved in evaluating ROI include the following:

  • Identify Costs. Start by identifying all upfront costs (e.g., city labor, expenses, infrastructure development, technology acquisition, installation, and integration), as well as operational costs (e.g., maintenance, monitoring, and training) associated with each of the initiatives.
  • Quantify Benefits. Determine the value generated by each initiative, including cost savings, improved efficiency, enhanced services, economic growth, clean air/water, and better quality of life. Assign a dollar value wherever possible or use other relevant metrics to measure impact.
  • Define KPIs. Establish KPIs that align with the objectives of each initiative. Example KPIs might include increased revenue, improved response times, minimized flooding, improved traffic flow, and happier residents. And make sure the KPIs you select are SMART: specific, measurable, achievable, relevant, and time bound.
  • Conduct Cost-Benefit Analyses. Compare the total costs with the total benefits estimated for each initiative to evaluate financial viability. Consider conducting a series of sensitivity analyses to assess the potential impact of different scenarios on the calculations.
  • Consider Long-Term Sustainability. For each initiative you will want to evaluate/understand the durability of any technology used, its ability to adapt to future needs/incorporate changes, and its scalability. These factors lead to understanding future costs (and cost savings), expansion possibilities, and/or revenue generation.

Step 3: Design & Delivery

When developing your BGI strategy, create a comprehensive implementation plan that outlines the specific actions, timelines, and resources required for the green infrastructure program. Start with critical areas whose projects and programs will maximize impact, and then determine the phasing from there. As you develop your plan, you will want to consider factors such as funding sources, regulatory requirements, and partnerships with relevant stakeholders, as well as any associated deadlines.

Before you go out to bid, develop guidelines and standards for design, construction, and maintenance of green infrastructure elements to ensure consistency and long-term effectiveness. Bid documents should specify—at a minimum—size, shape, flow path(s), vegetation, filter media, erosion control, and any maintenance as appropriate.

A critical component of the BGI•2 Framework is innovation. It is one thing to design a beautiful and effective series of BGI initiatives; what makes them extraordinary is to be able to understand performance, impact, and KPIs at a glance, and to know that they are performing as designed. Include a series of performance requirements in your bid/selection documents with a recommendation for utilizing one or several innovative technologies. Examples can include a series of flood and temperature sensors installed aboveground, flow or level sensors installed within sewer or storm systems, smart catch basins that remove nutrients, community engagement solutions that track BMP implementations and associated savings, and city-wide digital twin solutions that integrate BGI initiatives and associated data capture.

Once you have selected your solution provider, and as you go through the development process, be sure to include the entire team, e.g., representatives from design, construction, and maintenance, to ensure nothing is missed and everyone is on the same page throughout the entire program timeline.

Step 4: Impacts & ROI

And it’s in! Monitor and evaluate the program regularly to measure its performance, address challenges, and adapt as needed. Going back to the original list of priorities, we can identify a series of KPIs for each that you can select—try to limit it to one or two per initiative—to determine the success of your BGI•2 Program. Additionally, and quite importantly, understanding the ROI of each of these impacts by relating back to your earlier analyses provides a series of financial KPIs that you can monitor and incorporate into future applications.

Compliance & Water Quality

KPI: Reduced pollutant loading. Common pollutants include sediment, nutrients, heavy metals, and fecal coliform; measured via water quality sampling using automated samplers, sensors, and manual sampling via field crews or citizen scientists.

Flood Mitigation

KPI: Volume reduction. Effective monitoring requires either (1) pre- and post-construction monitoring through a variety of storm conditions, or (2) measuring flow in areas with BGI and in control areas/no BGI. Can measure aboveground and within sewer/storm systems.

Heat Island Mitigation

KPI: Surface temperature variations in areas with BGI and in control areas/locations with no BGI. Measured via temperature sensors that could be deployed as a low-cost sensor network or utilized during site inspections and maintenance visits.

Air Quality Improvements

KPI: Particulate matter (PM) reduction in areas with BGI and in control areas/locations with no BGI. Measured via a low-cost sensor network. Consider deploying local weather stations to correlate any changes in PM with weather conditions.

Recreation & Aesthetics

KPI: Community benefits. Measured via surveys that ask residents questions about community satisfaction, perceived quality of life, and utilization rates of BGI amenities, such as parks, urban forests, and community gardens.

For an even greater impact, you can engage the community through education and awareness campaigns to foster support, participation, and stewardship of your initiatives.

Conclusion

Utilizing a BGI•2 Framework offers communities of all sizes immense value in simplifying
the approach to implementing blue-green infrastructure initiatives, and, importantly, measuring their success. By incorporating BGI elements such as bioswales, rain gardens, and permeable pavements, communities can enhance stormwater management and flood control, improve
water quality, mitigate urban heat island effects, and promote urban recreation. However,
the true impact and success of these initiatives can only be realized through robust and accurate measurement. Innovative technology, such as advanced monitoring systems, remote sensing,
and data analytics, play a crucial role in quantifying and evaluating the performance of BGI programs. These technologies enable real-time monitoring, data collection, and analysis, providing valuable insights into the volume reduction of stormwater, improvement in air quality, energy savings, and other key metrics. With the ability to measure and track the effectiveness of green infrastructure and innovative technology, communities can make informed decisions, optimize resource allocation, and continually improve their resilience efforts. Ultimately, integrating blue-green infrastructure and innovative technology not only offers compliance benefits but also enhances urban resilience, livability, and the overall well-being of communities, as well as the
ability to fund projects in future.

The BGI•2 Framework described in this whitepaper outlines a step-by-step process any community can follow to create and implement their BGI initiatives, prove their value, and drive resilience.

For more information, contact erothman@stormwaterig.com. Stormwater Investment Group supports communities in their goals to adopt, fund, and execute innovative stormwater programs
to manage urban flooding and regulatory compliance, with each solution suite tailored to your specific challenges and opportunities.

References

City of Raleigh, North Carolina. 2023. Green Stormwater Infrastructure: Ecofriendly Development to Reduce Water Pollution. https://raleighnc.gov/stormwater/green-stormwater-infrastructure

Conservation in a Changing Climate. Green Infrastructure and Enhancing Resilience. https://climatechange.lta.org/green-infrastructure/

Headwaters Economics. 2022. Green Infrastructure: Cost-Effective Solutions to Flooding. https://headwaterseconomics.org/natural-hazards/green-infrastructure/

National Resources Defense Council. 2022. Green Infrastructure: How to Manage Water in a Sustainable Way. https://www.nrdc.org/stories/green-infrastructure-how-manage-water-sustainable-way

National Oceanic and Atmospheric Administration (NOAA). Green Infrastructure Options to Reduce Flooding: Definitions, Tips, and Considerations. https://coast.noaa.gov/data/docs/digitalcoast/gi-econ.pdf

PennFuture. What Is Green Stormwater Infrastructure? https://www.pennfuture.org/what-is-green-stormwater-infrastructure

The Nature Conservancy. 2023. Green Stormwater Infrastructure for Urban Flood Resilience. https://www.nature.org/content/dam/tnc/nature/en/documents/GSIanalysisREVFINAL.pdf

United States Environmental Protection Agency (U.S. EPA). 2023. What Is Green Infrastructure? https://www.epa.gov/green-infrastructure/what-green-infrastructure

U.S. EPA. 2022. Why You Should Consider Green Infrastructure for Your Community. https://www.epa.gov/G3/why-you-should-consider-green-stormwater-infrastructure-your-community

US EPA. 2019. Cost Effective Tools for Assessment of Infiltration at Green Infrastructure Stormwater Management Sites. https://cfpub.epa.gov/si/si_public_record_report.cfm?Lab=NRMRL&dirEntryId=348470

U.S. EPA. 2014. Using Green Infrastructure to Mitigate Flooding in La Crosse, WI: Assessment of Climate Change Impacts and System-Wide Benefits.  https://www.cleancreeks.org/241/Green-Stormwater-Infrastructure-Features

Watershed Management Group. Green Stormwater Infrastructure Overview and Resources. https://watershedmg.org/learn/resources/GSI

West Valley Clean Water Authority. Green Stormwater Infrastructure Features. https://www.cleancreeks.org/241/Green-Stormwater-Infrastructure-Features

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