LID methods that manage stormwater impacts at their source may also “buy back” capacity in existing storm sewer systems. The capacity of existing stormwater infrastructure remains constant while the developed area drained by this infrastructure continues to grow. By retrofitting existing developments and communities with LID and green infrastructure practices, and incorporating the same approach into new development projects, the volume of runoff draining to existing infrastructure can be reduced. Communities that utilize the LID approach may defer or eliminate the need to increase the capacity of existing stormwater infrastructure or to extend it in newly developed areas. Similarly, managing stormwater quality impacts at their source with LID BMPs or preventing them in the first place through behavior changes also offer economic efficiencies. When adopted across entire watersheds, such strategies may prevent widespread contamination, water resource impairment, and the need for costly cleanup and restoration initiatives.
ECONOMICS AT THE COMMUNITY SCALE
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Developers are also recognizing the cost efficiencies and value added benefits of using the LID approach for large-scale community and site development. Master planning projects that implement an LID approach have been shown to realize significant cost savings, ranging from thousands to millions of dollars, depending on the scale of the project. The LID neighborhood development proposal shown
in Chapter 6 employs an impact minimization approach that allows for a compact development envelope, requiring less pavement and maintaining 50 percent of the site in its pre-development condition. When compared to a development plan that uses a conventional design approach and an end-of-pipe stormwater management system, the LID concept’s required pavement was $1.4 million less expensive and its stormwater management infrastructure saved the developer over $200,000 (see p101). Both concepts yielded the same number of residential units. Access to shared open space resulting from LID practices, as well as adjacency to green infrastructure networks, provide amenities and lifestyle benefits that can increase a property’s marketability and value. 83
ECONOMICS AT THE SITE SCALE At the site scale, BMPs should be selected that achieve a project’s stormwater management strategy in a cost-effective manner. Retention and detention basins are typically the most cost-effective BMP, meaning that they manage the most runoff volume relative to their installation cost. However, not all sites have the available land area needed for the implementation of basins. Projects in dense urban areas may need to rely on less land-intensive but more expensive runoff reduction and retention methods, such as permeable pavements, vegetated roofs, and rainwater harvesting cisterns.