A team at the University of Mississippi researched how green stormwater infrastructure (GSI) could be used in northern Gulf of Mexico cities on sites 5 acres or smaller. GSI is designed to mimic how rainfall is absorbed by nature. Generally, GSI is implemented in massive projects, such planting along a miles-long boulevard or building a 5-acre rain garden. Such giant projects are impractical for cities with smaller budgets but who want to incorporate GSI.
This Mississippi-Alabama Sea Grant-funded project considered the effectiveness of different types of GSI on small development sites by performing computer modeling, and it evaluated implementation barriers, such as costs and regulatory limitations. The project researchers were Cris Surbeck, chair and professor of the University of Mississippi Department of Civil Engineering; Liya Abera, PhD, Environmental Engineering, at the university; and Kristina Alexander, attorney for the Mississippi-Alabama Sea Grant Legal Program.
The benefits of GSI
During this project, researchers identified and tested three methods of GSI for reducing stormwater runoff: grassy ditches, rain gardens and permeable pavement. Computer simulations of two sites, a commercial site in Biloxi, Mississippi, and a multi-residential site in Orange Beach, Alabama, assessed how effective each method was at controlling water after storms. The sites both permitted installing high percentages of impermeable areas – such as buildings and parking lots. But both cities’ ordinances also prohibited construction that increases stormwater runoff, meaning those sites have to capture the water in some way to adjust for the reduction in naturally-permeable areas.
The research showed that the most effective form of green infrastructure for reducing stormwater runoff could be different from one site to another. For the Biloxi site, rain gardens reduced runoff rates the most, but in Orange Beach, grassy ditches excelled. In both locations, however, the added GSI did not reduce runoff rates to pre-development conditions. Therefore, GSI generally works with gray infrastructure (think concrete storage areas), rather than replacing it.
The team summarized its findings in two reports, Stormwater Modeling Report and GSI Life-cycle Cost and Benefit Report, for any municipality to use to assess the wise use of GSI.
Implementation barriers
The study found that adding GSI to the Biloxi and Orange Beach sites would increase the costs of stormwater infrastructure but not significantly compared to the overall expense of development. Despite the costs, GSI brings social, environmental and health benefits. The report on life-cycle costs details the different ways GSI can improve a community. For example, by causing water to be absorbed rather than flushed into the Gulf of Mexico, GSI can reduce pollution. By adding green space and plants, GSI can improve air quality and the beauty of an area, and help natural cycles such as pollination. Out of all the types of GSI studied, rain gardens achieved the most in life-cycle costs as well as co-benefits and hydrological performance.
The team identified the primary legal barrier for GSI implementation as a lack of GSI mandates in municipal ordinances. Additionally, the team found that land use ordinances, as well as stormwater ordinances, need to incorporate GSI. The team developed a Best Practices guide for any city to use to incorporate GSI in its stormwater and land use ordinances. One example is to require high infiltration rates for large landscaped areas.
Conclusion
Thanks to a grant from the Mississippi-Alabama Sea Grant Consortium, a research team developed best practices for small sites in the northern Gulf of Mexico to reduce stormwater and improve the community. The computer modeling, life-cycle costs studies and legal analysis generated by the team are available for any city.