THE PLANNING PROCESS FOR LID - Low Impact Development and Sustainable Stormwater Management - page 84

estimated, and the various structural measures are evaluated to determine if they
will be completely effective in preventing any increase in non-point source load
generated from the parcel. Finally, the site plan is evaluated in the larger context
of the watershed: whether it will have implications for other water resource
impacts, such as water supply and wastewater, or perhaps produce secondary
impacts, such as major roadway requirements or infrastructure expansion. The
details of these steps are developed below, but the basic strategy should remain
the same: Avoid, reduce, and mitigate stormwater.
In arid watersheds such as the southwestern United States, the value of rainfall
for capture and potential reuse is too great to ignore, so that the method becomes
the first consideration, especially with respect to rooftop runoff, which is an
order of magnitude cleaner than street and gutter drainage. The prioritization
of LID methods will always change to reflect the local hydrologic cycle. Many
Southwestern communities, large and small, are severely limited in terms of
water resources, and their approach to stormwater management should begin
with a simple concept: “Capture the rain.” This is especially true in regions such
as southern California, where the population growth and land development have
vastly exceeded the water resources available.
4.2 OVERVIEW OF THE SITE DESIGN PROCESS FOR LID
The site design process for LID builds on the site planning process, which occurs
on the local level in most municipalities. The site design process for LID can be
thought of as 10 basic steps that are illustrated in Figure 4-7 and summarized in
Table 4-1. The 10 steps describe the entire development process from initial con-
sideration of regulatory conditions through final construction and maintenance.
Although the specific design solutions will vary, the process should be the same
under most circumstances. Each step could be the subject of lengthy discussion,
and articles have been written on many aspects of this process. However, to
lead the designer through the site design process, the checklist format shown in
Table 4-2 serves the need well.
An essential objective of the LID site design process is to maximize stormwater
runoff “prevention” through the use of nonstructural best management practices
(BMPs). When these measures are applied to the initial site design, the remain-
ing volume reduction need can be met by structural BMPs, for volume control,
water quality protection, and peak rate mitigation. An array of structural LID
measures are set forth in Chapter 6, including porous pavements with infiltration
beds, vegetated surfaces with infiltration beds, rain gardens, infiltration trenches,
constructed wetlands, vegetated roofs, rain barrels and cisterns, and others.
The site design process for LID is intended to promote development of opti-
mal stormwater management solutions in a cost-effective manner. Applicability
of some parts of the process can be expected to vary. For example, some non-
structural BMPs can be expected to be challenging to apply in those cases where
higher densities or intensities are proposed on the smallest of sites in already