| Summary: | 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.
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