Page 9 - July August 2017 Vol 35 No 2
P. 9
STATEWIDE By Kelli S. Richardson
Changing Landscape of Stormwater
with Low Impact Design
Stormwater runoff is considered a From stay-on-volumes, to infiltration and A bioretention area in a commercial office complex
problem in many urban environments. It water quality, different jurisdictions have
occurs when precipitation flows over the varying criteria that are being imple- Fairfax County, Va., roadway with vegetated swales
ground and impervious surfaces, such as mented, at times on a case-by-case basis.
concrete and asphalt, prevent the stormwa- For instance, Metro Nashville imple- StormTech System by ADS. - Photo from the ADS website
ter from naturally soaking into the ground. mented a voluntary low impact design for pre-development costs, which consist
Traditional design principles utilize large program in August of 2012. During this of any cost they incur during the land
detention or retention ponds to contain voluntary period, 23 percent of all grading purchase, due diligence, design, permitting
and treat stormwater runoff on project permits were issued to projects utiliz- and construction phases. These costs are
sites, concentrating flow to one area or ing low impact design principles. When passed along to the consumer in various
part of the site. Runoff must be controlled Metro’s mandatory program came online ways, depending on the type of develop-
to prevent property damage, flooding, in February 2016, the development and ment. They know how much pre-develop-
erosion and sediment deposits, and loss engineering communities were ready for ment costs can be incurred and still meet
of healthy vegetation, and to encourage the changes. Rebecca Dohn, with Metro
the recharge of groundwater. However, in Water Services Stormwater Division, in-
recent years, regulations and perception dicated that the voluntary period seemed
have evolved to include low impact design to provide a smooth transition from the
principles that focus on preventing con- traditional methods of stormwater design
centrated flows of stormwater from leaving to incorporation of low impact design
a site and on improving water quality. methodologies.
What is Low Impact Design? While Metro Nashville voluntarily
implemented their program, the City of
Low impact design, also referred to as Chattanooga was placed under a consent
green infrastructure, can be described decree from TDEC and the EPA to imple-
as many things. It is an engineering and ment a stormwater ordinance utilizing
land planning approach that is tailored to green infrastructure. The new stormwater
treating stormwater by utilizing the natural ordinance was implemented in December
environment. Green infrastructure is a of 2015 and required the first one-inch
concerted effort to minimize or prevent of rainfall to be held on-site with infiltra-
concentrated flows of stormwater from tion utilizing green infrastructure. Even
leaving a site and to allow for infiltration though the City conducted training for
to recharge the groundwater table. It can the engineering and development com-
improve water quality through natural munities, there was some resistance and,
filtration. In some instances, traditional in some cases, a misunderstanding of the
components of a development, such as ordinance requirements. Tony Kinder,
inlets, curbs and gutters, and piping can be City of Chattanooga Stormwater Manager,
eliminated through the use of low impact has indicated that the City stormwater
design practices. Green infrastructure ordinance is now better understood by the
can provide recreational opportunities or development community as a whole and
wildlife habitat through the incorpora- implementation, both through design and
tion of natural areas into the stormwater construction, has gone well.
design. Examples of low impact design
are bioretention areas, naturalized basins, Cost and Construction of Green
vegetated swales, underground detention, Infrastructure
infiltration trenches, green roofs, and tree
boxes with infiltration. In some circles, low impact design and
the term green infrastructure are still
State and Municipal Regulations are considered taboo. Change is hard, espe-
Evolving cially if it is enforced by a regulation or the
individual does not have the training or
Municipal and State regulations have adequate information to understand the
been evolving over the last 10 years to potential benefits of low impact design.
incorporate low impact design principles.
Developers look at their bottom line
8 TPW July/August 2017
