LID DESIGN CALCULATIONS AND METHODOLOGY - Low Impact Development and Sustainable Stormwater Management - page 125

6.8 NONSTRUCTURAL BMP CREDITS
The use of nonstructural BMPs is an important part of a project's stormwater man-
agement system and deserves to be credited properly in the calculation process.
However, nonstructural BMPs must be implemented correctly to be effective.
The use of these calculation credits for nonstructural BMPs must be documented
fully to the reviewing authorities. A system of checklists and worksheets has
been developed to facilitate this process, as summarized in flowcharts A, B, and
C in Appendix A.
The following nonstructural BMPs are “self-crediting,” in that the use of these
BMPs automatically provides a reduction in impervious area and/or stormwater
runoff (e.g., curve number) and a corresponding reduction in the required amount
of stormwater management. Additionally, use of these BMPs may be affected by
other regulations or guidance (master plans, zoning, subdivision, etc.). All of
these self-crediting BMPs are strongly encouraged:
• Protect sensitive/special value features.
• Protect/conserve/enhance riparian areas.
• Protect/utilize natural flow pathways.
• Cluster uses.
• Concentrate uses through smart growth.
• Minimize disturbed area.
• Reduce street imperviousness.
• Reduce parking imperviousness.
Although these BMPs are self-crediting and are not elaborated further in these
recommended procedures, checklists have been provided and should be com-
pleted by applicants when these self-crediting BMPs are being proposed.
The following nonstructural BMPs provide a quantitative stormwater bene-
fit and have been elaborated in Worksheet 3 in Appendix A as part of these
recommended procedures:
• Soil compaction minimization in disturbed areas
• Protection of existing trees (part of minimum disturbance)
• Revegetation and reforestation of disturbed areas
• Rooftop disconnection
• Disconnection of impervious areas (nonroof)
• Soil restoration
REFERENCES
1. Natural Resources Conservation Service, 1969-2001. National Engineering
Handbook , Part 630, Hydrology. Originally published as the National Engineering
Handbook , Sec. 2. sec4, Hydrology. http://www.wcc.nrcs.usda.gov/hydro/hydro-
techref-neh-630.html.