Low Impact Development Manual for Michigan - OSEH - University ...

Chapter 7
Structural Best Management Practices
This chapter focuses on structural Best Management
Practices (BMPs), Step 8 of the site design process for
LID described in Chapter 5. The work of Step 8 is to
figure out the most cost effective and environmentally
sound array of structural BMPs needed to accomplish
LID goals, once nonstructural BMPs have been applied.
This chapter provides guidance on selecting the proper
BMPs for a site. Specifically, this chapter:
• Discusses the BMP selection process, including
a matrix that compares the key applications and
functions of each BMP,
• Discusses cold climate considerations,
• Provides overviews of the BMP in fact sheets, and
• Discusses detailed information for each BMP such
as design considerations, construction guidelines,
stormwater calculations, and maintenance and cost
information.
This chapter also contains structural BMPs that may not
traditionally be viewed as low impact development, such
as water quality devices or retention basins. However,
having all available BMPs listed in this manual may be
helpful to municipalities or other regulatory agencies
that may use the LID manual as their design guidance
that accompanies a stormwater regulation.
BMP Selection Process
LID involves planning efforts that first prevent as much
stormwater runoff as possible on a site (Chapter 6) and
then mitigate stormwater runoff as efficiently as possible
(Chapter 7). Selecting BMPs which accomplish as
many stormwater functions as possible is important. At
the same time, meeting a certain function or level of
pollution control (Chapter 9) can require multiple BMPs
integrated at the site, thus creating a “treatment train.”
Such treatment trains direct stormwater to or through
multiple BMPs in order to achieve quantity and/or
quality stormwater management objectives. In addition,
implementing BMPs as part of a treatment train
can also provide a level of backup and needed redundancy,
which provides additional assurance if one BMP
does not work as designed (e.g., maintenance problems,
large storm event).
Some BMPs are more readily linked to other BMPs,
better lending themselves to treatment train configurations.
For example, water quality devices and
constructed filters are often used in treatment trains to
pre-treat runoff before entering different types of infiltration-driven
BMPs. In addition, vegetated swales and
vegetated filter strips link well with infiltration systems,
rain gardens, wet ponds, and constructed wetlands in
treatment trains.
How many of what BMPs should go where? Not all
structural BMPs are appropriate for each land development
at each site across Michigan’s many communities.
The selection process of the large array of structural
BMPs can be complex, as multiple factors are juggled.
The successful design process requires balancing technical
and nontechnical factors summarized in Figure
7.1. In order to assist communities in quickly comparing
the BMPs, Table 7.1 provides summary information on
potential applications, stormwater quality and quantity
functions, cost, maintenance, and winter performance
for each BMP.
Lawrence Technological University green roof, Southfield, MI
Source: Lawrence Technological University
LID Manual for Michigan – Chapter 7 Page 121