DESIGN OF LID SYSTEMS - Low Impact Development and Sustainable Stormwater Management - page 130

This concept has more to do with how you build on a parcel of land rather than
where you build. For each building envelope, we must confine soil excavation and
compaction to the area surrounding (and supporting) the structure. The limitation
of grading and earthwork begins by considering carefully how one will enter and
exit, how the structure is related to other contiguous buildings in terms of form
and function, and how the building will be situated to achieve optimal scenic
views of the surrounding community and environment. Historic site design has
included extreme examples of structures that totally disregarded this concept
in order to create a structure that became the center of community interest,
power, or religion. From temples to castles to cathedrals, all supporting structures
in the community were designed to draw attention and focus on the central
structure.
However, this type of site design has long since vanished into history
(although we still honor many remnant examples) and been replaced with
community designs that are generally bland and boring. Current site designs
have generally followed a practice of total site disturbance and alteration of the
land surface (and subsurface) in order to achieve some preconceived notion of
aesthetics.
7.2 STRUCTURAL MEASURES
A number of structural measures have been developed for stormwater manage-
ment and are presently in practice (Table 7-1). Volume reduction is the primary
design objective in LID designs, with pollutant transport reduction of equal
importance, and rate mitigation an element of all of the design concepts presented.
The three basic volume-reduction methods of infiltration, evapotranspiration and
capture-reuse are reflected in the four system designs presented in this chapter,
with a detailed description of each design approach. In an effort to avoid replica-
tion of data, the basic designs are very similar, and all of the measures listed are
variations on the basic theme. Since evapotranspiration is the essential element
of all vegetation-based designs, two variations are illustrated here.
The general heading “bioremediation” has been in use for some time and
has come to describe any stormwater management system that includes vege-
tation as a primary element. The term evolved from the use of vegetation in
retention basins to accomplish some nutrient uptake and allow ET to reduce the
standing pool in the basin. Since initial detention basin designs were intended to
be mowed lawn surfaces with no plantings allowed, this concept was a rad-
ical departure during the late 1980s, but offered great benefit in the correct
setting.
The two bioremediation designs described in this topic use vegetation in two
very different applications: one within the site at grade (rain garden) and the
second applying vegetation on the structure proper (vegetated roof). By their
nature they include both volume reduction and pollutant reduction, but with very
different design parameters.