Page 410 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

370 Cha pte r T e n

• Minimize clearing and grading.
• Provide dispersed areas for stormwater storage uniformly throughout the site.
• Disconnect flow paths.
• Keep predevelopment time of concentration.
• Employ public education and operational procedures.
• Maintain sustainability of LID practices and BMPs.
These can be summarized as follows: reduce new development, conserve existing and
natural systems, and disperse and disconnect the site stormwater.
New development introduces many conveyance mechanisms for stormwater which
need to be disconnected, reduced, or staged and planned. If these are not reduced or
mediated, then they can facilitate a rapid transport of runoff off-site and the resulting
environmental and flooding problems. Keeping water on-site and disconnecting flow
paths can also reduce pollutant transport off-site.
Typical built items that can become flow paths include

• Impervious roadways
• Roofs
• Gutters
• Downspouts
• Impervious drives
• Curbs
• Pipes
• Swales
• Impervious parking areas
• Grading
Reducing these items or designing them in alternative fashions can aid in lowering
the impacts of development and can also mean a reduction in construction costs.
However, development means we are building or engineering something, so for the site
to be accessible and functional, many of the surface features that may also become flow
paths will be installed. Some measures will need to be taken to minimize the impacts
these have on the site hydrology. The main focus of LID is to think micromanagement
and integrated management practices.
These practices can be multifunctional. In fact, many of the LID and IMP concepts
can be implemented in otherwise “nonfunctional” spaces. Dr. Allen Davis gives the
example of a grass swale or bioretention landscape strip being located in the area
needed for the overhang of fronts or backs of cars in parking spaces.
In response to the economic benefit of multifunctional best management practices
as promoted in the LID concepts, many agencies have expanded their stormwater
guides to include in detail some of the IMPs. On July 2, 2007, the North Carolina
Department of the Environment and Natural Resources released its new BMP manual.
There are chapters in this manual devoted to bioretention, permeable pavements, and
other BMPs that aid in attaining the LID concepts.
Then, in 2007, the Environmental and Water Resources Institute (EWRI) of the
American Society of Civil Engineers (ASCE) formed an LID committee in its Urban