1. Chapter 5 Comprehensive Stormwater Management: Non-Structural BMPs
      1. 5.1 Introduction
      2. 5.2 Non-Structural Best Management Practices

Pennsylvania Stormwater Best Management Practices Manual
Chapter 5
Chapter 5 Comprehensive Stormwater Management: Non-Structural BMPs
The terms “Low Impact Development” and “Conservation Design” refer to an environmentally sensitive
approach to site development and stormwater management that minimizes the effect of development
on water, land and air. This chapter emphasizes the integration of site design and planning techniques
that preserve natural systems and hydrologic functions on a site through the use of Non-Structural
BMPs. Non-Structural BMP deployment is not a singular, prescriptive design standard but a
combination of practices that can result in a variety of environmental and financial benefits. Reliance
on Non-Structural BMPs encourages the treatment, infiltration, evaporation, and transpiration of
precipitation close to where it falls while helping to maintain a more natural and functional landscape.
The BMPs described in this chapter preserve open space and working lands, protect natural systems,
and incorporate existing site features such as wetlands and stream corridors to manage stormwater at
its source. Some BMPs also focus on clustering and concentrating development, minimizing disturbed
areas, and reducing the size of impervious areas. Appropriate use of Non-Structural BMPs will reflect
the ten “Principles” presented in the Foreword to this manual, and will be an outcome of applying the
procedures described in Chapter 4.
From a developer’s perspective, these practices can reduce land clearing and grading costs, reduce
infrastructure costs, reduce stormwater management costs, and increase community marketability and
property values. Blending these BMPs into development plans can contribute to desirability of a
community, environmental health and quality of life for its residents. Longer term, they sustain their
stormwater management capacity with reduced operation and maintenance demands.
Conventional land development frequently results in extensive site clearing, where existing vegetation
is destroyed, and the existing soil is disturbed, manipulated, and compacted. All of this activity
significantly affects stormwater quantity and quality. These conventional land development practices
often fail to recognize that the natural vegetative cover, the soil mantle, and the topographic form of the
land are integral parts of the water resources system that need to be conserved and kept in balance,
even as land development continues to occur.
As described in Chapter 4, identifying a site’s natural resources and evaluating their values and
functional importance is the first step in addressing the impact of stormwater generated from land
development. Where they already exist on a proposed development site, these natural resources
should be conserved and utilized as a part of the stormwater management solution. The term “green
infrastructure” is often used to characterize the role of these natural system elements in preventing
stormwater generation, infiltrating stormwater once it’s created, and then conveying and removing
pollutants from stormwater flows. Many vegetation and soil-based structural BMPs are in fact “natural
structures” that perform the functions of more “structural” systems (e.g., porous pavement with
recharge beds). Because some of these “natural structures” can be designed and engineered, they are
discussed in Chapter 6 as structural BMPs.
Non-Structural Best Management Practices
This Manual differentiates BMPs based on Non-Structural (Chapter 5) and Structural (Chapter 6)
designations. Non-Structural BMPs take the form of broader planning and design approaches – even
principles and policies – which are less “structural” in their form, although non-structural BMPs do have
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