Environmental Valuation & Cost-Benefit News

Abstract: This paper presents a simple model for assessing the cost-effectiveness of investments in low impact development (LID) for reducing combined sewer overflows (CSOs) in urban watersheds. LID systems, including green roofs, porous pavement, and stormwater treatment wetlands, are site-specific controls for stormwater runoff. If applied throughout a watershed, LID systems like these can reduce the amount of runoff entering the sewer system and reduce CSOs. To be conservative, we focus solely on the function of LID systems as stormwater management techniques, neglecting the other environmental benefits commonly associated with these technologies. A model is presented that can be used to simulate the cost-effectiveness of reducing CSOs through incremental installation of LID technologies across urban watersheds, when they are introduced alone, or in combination with conventional CSO abatement technologies. The potential reduction in CSOs resulting from various levels of LID adoption is simulated using a modified Rational Method. A life-cycle cost analysis is used to compare LID with other alternatives. Given that LID implementation on private property leads to reduced CSOs, a cost sharing scheme is presented that divides the total LID cost into a private cost fraction (born by the property owner) and a public cost fraction (provided by a public agency). The implications of such a policy are discussed with reference to a CSO-shed that drains to the Gowanus Canal (Brooklyn, NY). The results indicate that individual LID systems have differing levels of cost-effectiveness in terms of CSO reduction, but that under a variety of performance and cost scenarios a public subsidy to encourage LID installation represents a cost-effective alternative for public agencies to consider in their efforts to reduce CSOs. Future areas of research in this field are outlined.

Keywords: Urban stormwater; Low impact development; Combined sewers; Cost analysis; New York City

by Franco Montalto 1, 2, Christopher Behr 3, Katherine Alfredo 5, Max Wolf 6, Matvey Arye 3 and Mary Walsh 3
1. Design Dynamics LLC, 220 61st Street, Suite 2B, West New York, NJ 07093, United States
2. The Earth Institute at Columbia University, S.W. Mudd, Room 606A, 500 West 120th Street, New York, NY 10027, United States; Telephone: +1 212 854 3219/201 453 9300; fax: +1 212 8546267
3. The Cooper Union for the Advancement of Science and Art, 51 Astor Place, New York, NY 10003, United States
4. HDR|HLB Decision Economics, 8043 Colesville Road, Suite 910, Silver Spring, MD 20910, United States
5. Department of Civil, Architectural, and Environmental Engineering, University of Texas, Austin TX 78712, United States
6. WernerSobekNewYork, 375 Park Avenue, Suite 1507, New York, NY 10152, United States

Landscape and Urban Planning via Elsevier Science Direct www.ScienceDirect.com
Volume 82, Issue 3; September 24, 2007, Pages 117-131
http://dx.doi.org/10.1016/j.landurbplan.2007.02.004