Historically, the work of stormwater engineers has involved capturing rainwater and conveying the flows offsite as quickly as possible. This approach led to the development of a vast system of large, centralized treatment facilities handling millions of gallons of stormwater annually – a very efficient, but not very environmentally-minded solution.
After decades of development that prioritized efficiency over ecology and short-term convenience over long-term benefits, there has recently been a major shift in how we approach this design problem. Green Stormwater Infrastructure (GSI) is a subset of low impact development (LID), an approach focused on stormwater management through techniques that mimic and/or restore the natural water cycle. GSI aims to decrease the amount of stormwater conveyed to these large municipal systems and to reduce the impacts of overflows and flooding events associated with their failures. This means that stormwater engineers are trading pipe flow rate equations for soil infiltration rates and designing systems that keep rainwater on the site, where it lands, thereby returning rainfall to the natural environment after cleaning it.
A byproduct of this shift is that not all land developers and owners understand the advantages of adopting green stormwater infrastructure approaches. The success of these systems not only rests in their design, installation, and maintenance, but also in the successful education of those impacted by them. Site owners and developers must see and understand the value of these systems to support the architects and engineers who design them.
Here are nine talking points for designers to explain to owners and developers what they can expect from LID and GSI strategies – and why they’re often the better solution to stormwater management:
Low Impact Development techniques have positive environmental impacts
Evidence shows that the techniques of low impact development have a beneficial impact on the environment ( GSI performance research). By promoting the reduction of hardscapes and the increase of on-site infiltration, GSI results in sites that produce less surface water runoff, less pollution, better air quality, less erosion, and have reduced flooding impacts. Infiltration also recharges the groundwater aquifer and reduces the damage that urban run-off has on fresh water bodies (lakes and streams) and salt water bodies (estuaries and oceans), while also recharging base flows that are essential to fish and other wildlife.
Low Impact Development techniques include a greater diversity of drainage solutions
“Conventional” stormwater control facilities include catch basins, storm drain pipes, conveyance channels, and vault-type facilities. These structures and pipe networks provide a “capture and convey” approach to stormwater management. The techniques of LID provide a greater suite of distributed and infiltrative flow management approaches such as rain gardens, cisterns, pervious pavements and plantings (preservation of native areas/mature trees and restoration of landscapes and tree planting) techniques.
Low Impact Development techniques distribute stormwater management across the site
Through varied surface collection alternatives and widespread infiltration areas, LID techniques can provide a diversity of discharge locations — this supports maintenance of natural discharge locations and mimics the natural water cycle by promoting distributed stormwater management and infiltration. This also reduces the risk and impacts associated with failure of a single type of facility or single discharge point.
Green Stormwater Infrastructure techniques can be customized
The greater suite of GSI techniques can be customized to control the quantity and quality of stormwater run-off that more closely mimics native hydrology. The optimization of size, type and location can reduce construction costs and increase the usable site area. These systems can also be designed to fit into both urban and non-urban environments, which reduces the visual impacts of storm drainage infrastructure and can improve the aesthetics of a site.
These systems can provide multiple functions
Unlike conventional gray systems, green infrastructure systems are not limited to a single function. Permeable pavement facilities are a stormwater control and a travel pathway for site circulation. Bioretention facilities promote infiltration (flow control) and provide water quality while also increasing landscape area and providing habitat for native bird and insect species.
Low Impact Development facilities can improve the aesthetic of a site
Pipes and catch basins are not pretty. Even the most attractive, artist-rendered manhole castings are merely accepted as a requirement of site development. Well-integrated green infrastructure facilities, including landscaped raingardens and conveyance swales, provide green space that enhances site aesthetic. For an owner, this means increased marketability, increased property values and healthier environments for their tenants.
Green Stormwater Infrastructure facilities can be more economical
Green infrastructure facilities can cost less to construct and maintain because there is often less below-grade infrastructure. Space that was given over to large detention facilities can now be employed for other uses and benefits. This means that owners have more usable land area to serve users and to increase the developable area of a site.
Green Stormwater Infrastructure facilities can provide educational value
Where does rainwater go? How does surface water impact our communities? How can we manage the pollutants that surface water carries? The surface waters and treatment components of green infrastructure systems can provide an educational component to sites.
Low Impact Development is required by law
Decades of polluted surface water reaching our streams and lakes has had an undeniable effect on our environment. Sediment, hydrocarbons, heavy metals, and other toxic materials are contaminating beach and waterfronts and killing wildlife. Flooding events and erosion damage private properties and public rights of way. The Environmental Protection Agency Clean Water Act is working to reverse these impacts. Jurisdictions of all sizes are part of this process and each owner and developer must comply with the requirements of stormwater discharge permits in a manner compliant with the authority having jurisdiction.
Low Impact Development has long term economic, ecological, and social benefits that improve the bottom line for developers and owners.
The promotion of infiltration and the reduction of impervious surfaces reduces the stormwater volumes that inundate aging drainage systems, cause flooding failures, and send pollutants to our natural streams and lakes. Less surface run-off saves money associated with facility maintenance and water treatment. LID techniques promote the preservation of vegetation and infiltration and the reduction of impervious surfaces. Increasing landscaped areas for people and wildlife. Finally, it promotes healthier environments, people, and community economics. Simply put, LID is good business.
Lolly Kunkler and Patty Buchanan are civil engineers at MIG|SvR.