Stormwater Concepts-No Adverse Impact.
The scope and expectations of Stormwater Management have changed dramatically in the last few years, moving away from a purely flood control perspective toward a green infrastructure approach protecting the sustainability of our rivers and watersheds (PaDEP 2006). The first transition occurred when we as a profession realized that we could start to address water quality issues in our flood control based detention facilities, by creating naturalized basins or stormwater wetlands. Our next advance has been to integrate Low Impact Development concepts, such as pervious pavements, green roofs and bioretention, into the landscape to minimize the adverse effects of land form change and to address stormwater volume. As our profession becomes more confident in the performance and longevity of our BMP tools, we are again progressing, moving toward a “No Net Impact”, or better stated, “No Adverse Impact” design goal. To move toward a No Adverse Impact (NAI) approach, it must be understood that this can only be achieved when viewed from a systems perspective when all components are part of solution to include hydrologic, chemical, and biological processes, land use planning, and infrastructure sustainability,. While it is clear that as a profession (Davis et al 2007) we can now demonstrate that Best Management Practices can greatly reduce adverse effects, we need to have a better understanding of the linkages and unit processes to apply a no adverse impact design concept. It is not enough to understand that a specific BMP can remove a percentage range of pollutants, what must be understood is how a BMP operates in a specific dynamic environment of receiving flows and pollutants, for its climate and soil conditions, and how it translates to a system of BMPs on a watershed scale. The understanding of BMP performance is moving from a planning basis to an engineered solution. Clearly land use planning is a major component in incorporating NAI as it is a mistake to believe that we can change a wooded area to an industrial center with no impact. Even if possible, this would not be desirable as the value of green space would be devalued. A complete view of the impact of development on our waters would include other environmental issues in addition to stormwater. By incorporating land use through trading, infill, and brownfield / grayfield redevelopment the goals are achievable. With this in mind, a concept of “No Adverse Impact Plus” or “Positive Impact Development” can be further introduced. Through a watershed planning / management process or a jurisdiction-wide planning process, several already impaired watersheds or areas can be identified where the “No Adverse Impact” approaches may not be enough to protect or maintain the desired eco-system. Restoration of stream corridors or retrofiting older developed areas may be needed as part of the solution. A long term vision of the green infrastructure NAI approach requires a sustainable infrastructure support program that includes inspection, maintenance and eventual replacement of our stormwater controls. Designing to meet NAI goals requires a life cycle view. Reduced operational performance or failure is expected of all engineering structures, and clearly inspection, maintenance and replacement programs are needed.
|Main Author:||Traver, Robert G.|
|Other Authors:||Davis, Allen P., Hunt, William F., Cheng, Mow-Soung.|