May 02, 2019 | Water in the West | Insights
Walking across the Stanford campus, it’s not unusual to see flocks of active undergraduates playing soccer, serving volleyballs or just generally enjoying one of the many inviting lawns. At first glance, the scene seems like a poster for the benefits of college in California come to life. What the casual observer—and even most students—might not realize is that many of these spaces are serving multiple purposes. The soccer field, for instance, is also a detention pond, storing stormwater and preventing flooding, while also recharging our precious groundwater. The volleyball court, is a stormwater sand filter, slowly treating polluted runoff. The popular Meyer Green includes permeable pavement and landscaping to capture stormwater and provide a sunny recreation spot for students. Elsewhere, important changes are also underway. Some campus irrigation is now supplied by harvested rainwater, parking lots throughout campus have been installed using porous pavement and biofilters have been installed to improve aesthetics and infiltrate stormwater runoff.
Figure 1: Meyer Green at Stanford University illustrates an example of how many spaces on campus can serve dual purposes. Photo credit: Stanford News Service.
All of these natural systems are powerful examples of the way that green infrastructure—in contrast to more traditional grey infrastructure (e.g., pipes, engineered detention ponds and treatment plants)—can reduce the flood risk by mimicking the hydrology of undeveloped “natural” systems. In this way, green infrastructure mitigates the risk posed by stormwater runoff to urban centers by harnessing natural processes, including soaking up excess water and slowly releasing it, while enhancing the livability of our communities. As the Stanford examples illustrate, green infrastructure is often designed to provide a diverse set of environmental, social and even economic benefits.
Because of this versatility, green infrastructure has become a particularly attractive way to cope with the difficulty and cost of modernizing water infrastructure and management. At Stanford, a diverse group of researchers are studying how to integrate green infrastructure into our current systems, whether in the form of advancing technical knowledge about how green infrastructure operates or developing tools to measure the variety of benefits provided by these projects. In this piece, we dig in to how these research efforts on the frontiers of green infrastructure fit together to tackle bigger issues of climate change, urbanization and aging infrastructure.
Understanding the Benefits of Green Infrastructure
Natural systems are the best way to capture and sustainably manage stormwater. As a result, green infrastructure is often first considered as a way to improve stormwater management. However, there are a multitude of other benefits that green infrastructure can provide. A team of researchers from the Stanford-based Natural Capital Project (NatCap) is currently investigating how to quantify these additional benefits, including noise and heat reduction, increased recreational opportunities and urban habitat creation, that are linked to green infrastructure (Figure 1). From NGOs to multilateral institutions or local governments, there is an increased interest in measuring these benefits to design more livable cities. The NatCap team is addressing this need by researching the impact of green infrastructure on air temperature, coastal protection and mental and physical health. In addition to these primarily local co-benefits, some types of green infrastructure also help mitigate broader environmental issues, namely climate change and biodiversity loss, by storing carbon and providing habitat for diverse species.
Figure 2: Benefits of green infrastructure can include: a) reducing air temperature, which alleviates public health risks during heat waves; b) supporting nearby crop pollination or providing forage for honey bees; c) protecting coastal properties and communities by buffering against coastal hazards; d) providing recreation opportunities; e) improving mental health, i.e., improving cognitive functions or reducing stress levels simply by seeing or being in nature; and f) reducing air and noise pollution, although the magnitude of these effects is debated.
To factor these benefits into infrastructure decisions, the team also develops modeling tools aimed at urban practitioners. For example, NatCap is now expanding its software suite InVEST (Integrated Valuation of Ecosystem Services and Tradeoffs) to include the multi-sector benefits of green infrastructure. The software tool translates maps of urban environments, with various implementations of green infrastructure, into maps of benefits to communities. The goal is for this tool to enable communities to better identify and quantify the diversity of benefits related to green infrastructure when making stormwater management decisions.
One of these benefits of particular interest to researchers at Stanford is the ability of green infrastructure to improve water quality. Green infrastructure provides immediate infiltration capacity for rainwater, which can prevent stormwater from flowing over impervious areas and gathering various urban pollutants. Modeling and empirical studies of green infrastructure performance have documented positive changes in water quantity: reduced peak flow, runoff volumes and increased groundwater recharge. However, managing stormwater quality remains an important area of research. Many pollutants are present in stormwater including nutrients, suspended sediment, metals and trace organic contaminants (e.g., detergents, pesticides and pharmaceuticals).
Recognizing this need, researchers at Stanford’s Engineering Research Center for Re-inventing the Nation’s Urban Water Infrastructure (ReNUWIt) are developing green infrastructure systems that are optimized to remove these pollutants. Improvements to current green infrastructure include modifying the hydraulic properties of the systems, optimizing plant and fungal processes and replacing the typical geomedia (generally a mix of compost and sand) with alternatives that provide better pollutant removal.
This research has been piloted in Sonoma County and Los Angeles. Stanford researchers worked with Sonoma County Water Agency and partners in the City and County of Los Angeles to install innovative treatment filters to see how different types of geomedia (e.g., woodchips, sand, biochar and compost) can remove pollutants. This research is of particular interest to arid cities like Los Angeles, where the filters can act as a pre-treatment for stormwater before it’s reused for water supply. Stanford researchers have found that biochar, a type of charcoal, removes more than 99% of certain pollutants like pharmaceuticals and pesticides. They have confirmed biochar can also be used to reduce concentrations of fecal indicator bacteria, which are a proxy for fecal contamination.
Figure 3: Photo of field-set up of filter experiments in Sonoma County. Each column includes a different type of geomedia such as woodchips, biochar, straw or a combination. Stormwater runoff flows upward through each filter to be treated. Photo credit: Marc Teixido (UC Berkeley).
In addition, plant and fungal processes may play a role in breaking down chemical pollutants. ReNUWIt researchers have found that plants and fungi can degrade urban-use pesticides and roadway pollutants such as deicing fluids. Design improvements like these to green infrastructure may help cities comply with water quality standards at the watershed scale. One finding of this research is that small improvements to performance (at the individual best management practices level) may result in large improvements in water quality at the watershed scale, resulting in potential for significant cost savings.
Working to Implement Green Infrastructure
With the promise of providing a suite of benefits, green infrastructure can be a great asset for urban environments by achieving multiple goals at the same time. Successful implementation, however, is still a major challenge.
One issue is that some benefits remain difficult to measure quantitatively across projects. Should we invest in a project that makes this community healthier over a project that makes another community less vulnerable to heat waves? How can we weigh improvements to quality of life in comparison to project costs? How should we measure and compare these benefits in a methodical way?
One way to deal with these types of questions is to use multi-objective assessment or try to translate all benefits into the same metric (e.g., economic value), but determining how much communities value each type of benefit is complicated. Additionally, planners need to consider other factors that will make the project a success: the history of the site, multiple (and sometimes conflicting) priorities by stakeholders, community engagement and preferences for one type of project over another.
For a test case, NatCap has been working in the San Francisco Bay Area with multiple planning and conservation organizations to understand the value of local natural assets in hopes of protecting them in the future. Arguably the most challenging part of this endeavor has been navigating the priorities and relationships between various stakeholders to define the most meaningful questions and a clear path forward.
The project team decided to focus on a network of open spaces of special importance for the region. The research delivered quantitative measures of a range of ecosystem services— coastal protection, recreation and stormwater retention— provided by the open spaces, which can be used in regional urban planning. Some of this work is being implemented in the Bay Area Greenprint website, which is an online tool that planners in the Bay Area can use to incorporate built natural resource conservation in policy and action. The effort is led by multiple conservation organizations and hopes to mainstream green infrastructure information in regional and urban planning.
Despite clear potential benefits, communities around the world face a series of barriers in practically implementing and scaling green infrastructure systems. Finding funding is most often identified as one of the primary barriers by utilities, municipalities and regions wanting to implement new green infrastructure projects or expand the scale of existing green infrastructure projects. It is no secret that the water sector is cash-strapped, but funding challenges can be particularly pronounced when it comes to financing innovative water solutions.
Financing can be difficult for many reasons: green infrastructure systems are distributed instead of centralized, the technology is new and uncertain and the solutions are site-specific. One way to cross this funding barrier is by engaging with other sectors that can benefit from green infrastructure through better communication and tracking of multi-sector performance metrics. Water in the West has investigated mechanisms to help cities overcome this challenge by developing a case-study based framework for implementing green infrastructure that could be used to attract a diverse set of funders.
Figure 4: Conceptual framework organized around a circular process that includes six steps.
Through this high-level and global investigation, researchers at Stanford are seeking to identify how successful projects implement multi-sector performance metrics in the hopes that this can be replicated elsewhere. For example, better tracking of social benefits related to green infrastructure may incentivize investment in projects from organizations or funds interested in social justice. Perhaps one of the biggest questions this research is seeking to address is how different types of risk (e.g., social versus technical) impact financing opportunities. Looking at where and how risk has been mitigated around the globe may provide helpful guidance for other projects to attract investors who may be concerned about the risks associated with undertaking the development of green infrastructure. While there is no single recipe for success, especially given the context-specific nature of green infrastructure, there are universal elements, such as measuring and clearly communicating social benefits like increased property values that can help any project access broader funding sources and achieve success.
Despite these challenges, many cities around the world have achieved success in installing green infrastructure systems. These implementers have used different strategies to make these projects a reality. In an effort to compile these examples, researchers at Water in the West and ReNUWIt have identified innovative financing approaches being used in the U.S. By documenting these efforts through a peer-to-peer learning tool (Figure 5), the hope is to help project implementers connect and explore the possibilities of doing things differently.
Figure 5: The Living Map, created by Newsha Ajami, who directs the Urban Water Program at Water in the West, and her team highlights successful innovative water financing efforts around the country designed to be implemented at various scales. The case studies feature a wide variety of mechanisms; for example, some are market-based systems like credit and permit trading used to implement green infrastructure projects built to manage stormwater runoff.
Bringing green infrastructure into the mainstream is challenging, however collaborative and interdisciplinary research efforts like those being conducted here at Stanford are one promising path around the barriers that exist, including scalability and funding. Our hope is that as the number of examples showing how green infrastructure can be used to generate multi-sector benefits increases, more cities will see these natural systems as a viable alternative and in some cases complementary to traditional gray-infrastructure approaches. In turn, this leverages greater opportunities for collaborative funding to implement win-win solutions for people, the environment and the economy.