Page 411 - The Engineering Guide to LEED-New Construction Sustainable Construction for Engineers

Low-Impact Development and Stormwater Issues 371

Water Resources Research Council (UWRRC). It has been recognized that there is a
great need for research and development of manuals, best practices, and standards with
respect to the LID concepts. The first three initiatives started by this committee are to
look into the technology associated with green roofs, porous and permeable pavements,
and rainwater harvesting. In 2008 through 2010, additional initiatives were added
including modeling, ultra urban issues, and green streets or highways.
Another recent action that is helping to foster the LID trend in design and development
is a new credit added to the USGBC LEED for Schools rating system in 2007 which was
further updated in LEED 2009. In the Sustainable Sites category an additional credit was
added called site master plan. Basically, this credit requires a master plan to be prepared
for a school location covering current and planned development, and in this master plan
the future plans should include adhering to at least four out of seven specified SS credits.
The specified credits are SSc1: Site Selection; SSc5.1: Site Development: Protect or Restore
Habitat; SSc5.2: Site Development: Maximize Open Space; SSc6.1: Stormwater
Management: Quantity Control; SSc6.2: Stormwater Management: Quality Control;
SSc7.1: Heat Island Effect: Non-Roof; and SSc8: Light Pollution Reduction. If one thinks
about these credits, most together promote many of the LID concepts.
Combining a number of credits is very similar to the concept of integrating various
management practices. For instance, in most cases one needs landscape areas for
aesthetics, but why not also use these for stormwater management? Shading is needed
for urban heat island effect reduction, but if trees are used, the tree islands can also be
used for stormwater management.
There are a number of issues that must be addressed when adopting LID practices
for good design. Some of these include the following:

• Make sure that flood control is adequately considered.
• Be careful that water is not infiltrated where it might cause structural damages
such as under some impervious pavements (hydrostatic forces), under buildings
(water damage), and into unstable slopes.
• Some of the quasi-structural BMPs may not be sustainable since they may not
appear to have readily noticeable site functionality. They need some way of
fostering permanence. Some methods to do this may be structural such as
adding rock walls; others may be nonstructural such as establishing conservation
easements for infiltration areas.
• The decrease in paved areas must take into consideration safety and access
concerns.

LID and Land Development Design
This chapter in no way attempts to be a comprehensive resource for LID. It would take
an entire book or manual to even start any detailed design. However, a few of the main
concepts have been reviewed, and this chapter gives some site design examples and
an example method to perform some calculations on one of the newer stormwater
management technologies that may be used for LID designs. Four other commonly
referenced resources for information on how to incorporate LID into land development
design are

• Prince George’s County, Department of Environmental Resources (1999), Low-
Impact Development Design Strategies: An Integrated Design Approach, Prince
George’s County, MD.