RESEARCH COLLOQUIUM ON COMPUTATIONAL SOCIAL SCIENCE/DATA SCIENCES – Seth Brown – To Be or Not To Be: Introducing the Green Stormwater Infrastructure Social Spatial Adoption (G-SSA) Model

November 15, 2019 @ 3:00 pm – 4:00 pm
Karen Underwood

Research Colloquium on Computational Social Science/Data Science

Dr. Seth Brown
Steam Solution LLC
National Municipal Stormwater Alliance

To Be or Not To Be: Introducing the Green Stormwater Infrastructure Social Spatial Adoption (G-SSA) Model

Friday, November 15, 3:00 p.m.
Center for Social Complexity Suite, 3rd Floor Research Hall

All are welcome to attend.


The use of incentives in stormwater programs is a common feature that is used to motivate private property owners as well as land developers to adopt specific types of stormwater management infrastructure at the site or parcel level. While incentives for land developers, such as reduced plan review time or reduced plan review fee for projects that utilize specific BMPs, such as green stormwater infrastructure (GSI), are helpful policies in driving implementation of innovative stormwater practices, this implementation is limited to land development activity. Approximately 75% of existing impervious cover is associated with land development activities that took place prior to federal legislation focused on urban stormwater runoff. The implication of this is that a majority of impervious cover across the U.S. discharges runoff that is either inadequately managed or not managed at all. Until we address these existing areas, impacts from these areas will continue to impact our waters. This is reflected by evolving regulations that require a certain amount of existing impervious cover to be retrofitted to provide stormwater management. Many cities, such as Milwaukee, Seattle and Atlanta, also have retention volume goals as part of a regulatory program as well as an effort to increase the resilience and sustainability of urban areas.

The motivation to retrofit existing impervious areas is a driver to retrofit both public and private lands. Public rights-of-way (ROWs) are often challenging to work within, and there is a limited amount of public ROW available. Overall, 60% of land in the U.S. is privately held, with large portions of these areas located in large public parks in Mountain Region states. The result is that many states have private land ownership rates at 80% or higher; clearly this is a need to find ways to locate urban stormwater retrofits on private lands.

The default method of incentivizing private land owners to adopt onsite stormwater infrastructure is a stormwater fee reduction according to the 2018 Black and Veatch Stormwater Utility Survey. The limitation with this approach comes in when a community does not have a stormwater utility established, which is the case for at least 2/3 of the regulated stormwater entities in the country. And even if a utility exists, the fees are often not high enough to make economic sense for onsite adoption when considering payback periods and other financial metrics. The reason for this is simple – stormwater utility fees are set at a level/rate to pay for needed stormwater programmatic and implementation rather than to create an effective financial incentive for private parcel owners to adopt BMPs onsite. The result of this are participation rates in incentive-based stormwater infrastructure on-site investments of 2-5% or lower associated with traditional incentive programs, which also include cost-sharing and subsidy programs as well. Due to this reason, communities are considering market-based approaches, such as stormwater credit trading, that can reward private property owners in a more robust way for onsite BMP adoption.

While market-based programs hold much promise, the focus of research in this area has been (rightly) on program architecture and policies with the view of “if we build it, they will come”. However, this leaves a void in understanding on how parcel owners will respond to market-based option. Questions regarding the motivations for adoption, how decisions on adoption are made, and how adoption on parcels affect adoptions in neighboring areas or parcels. This presentation will outline research done to begin to address the “consumer behavior” view of BMP adoption. Specifically, a socio-economic model based upon cellular automata-style agent-based modeling will be presented to illustrate a method to capture the adoption of GSI across multiple urban neighborhoods that comprise a city-wide landscape.

This model – the Green Stormwater Infrastructure Social Spatial Adoption (G-SSA) model – provides insights on neighboring effects, spatial dynamics, and decision-making aspects of GSI adoption based upon social theory. Model sensitivity analysis highlights the significance of social and spatial model elements to overall GSI adoption rates and pattern. An applied G-SSA model has been developed and explored to simulate the complex emergent patterns for GSI adoption across a specific cityscape (Washington, D.C.). Applied G-SSA model output is consistent with expected model behavior as well as observed and document GSI adoption patterns in Washington, D.C.

Seth Brown is the Principal and Founder of Storm and Stream Solutions, LLC, a consulting firm providing a range of services in the stormwater sector. He is the Executive Director of the National Municipal Stormwater Alliance (NMSA), which is a 501.c.3 representing state and regional organizations focused on stormwater issues. Seth is also the Senior Stormwater Advisor with the Water Environment Federation (WEF) where he supports national-level technical and policy initiatives associated with stormwater issues. He has a PhD from George Mason University in the Department of Civil, Environmental and Infrastructure Engineering and is a licensed professional engineer in the state of Maryland.