Across the United States, aging water infrastructure is creating challenges for water management. Combined sewer systems are pumping toxins into estuaries, bays, lakes and other water bodies and overflowing during extreme precipitation events into urban and residential areas. At the same time, coastal communities are being heavily damaged from extreme storm events and sea level rise. Several experts contend that “natural infrastructure” such as healthy wetlands can provide many of the same benefits of traditional man-made infrastructure at a much lower investment and maintenance cost. Natural infrastructure approaches include forest, floodplain and wetland protection, watershed restoration, wetland restoration, and conservation easements.
Low-impact development (LID) “is an approach to land development (or re-development) that works with nature to manage stormwater as close to its source as possible.” (USEPA) “Green infrastructure” projects utilize “systems and practices that use or mimic natural processes to infiltrate, evapotranspirate…or reuse stormwater or runoff on the site where it is generated.” (USEPA) These three terms, “natural infrastructure,” “green infrastructure,” and “low-impact development” are often used interchangeably and are not universally defined. However, green infrastructure and LID are most often used in urban and developed areas which are typically far more disturbed than rural sites and they utilize a more of an engineered solution – examples include bioswales, permeable pavement, green roofs, etc. Natural infrastructure relies more on existing and/or restorable natural resources such as natural floodplains, wetlands and forests to provide the same benefits.
For example, in southern Maine, Sebago Lake is the primary source of drinking water for the greater Portland region. Although Sebago Lake is not in an urban area, development, forest clearing and population growth were jeopardizing the water quality of the lake. So the Portland Water District (PWD) embarked on an effort to purchase conservation easements with local land trusts to preserve natural infrastructure (i.e., forest land, natural buffers and wetlands) that experts estimated would save the PWD more than $122 million over 20 years (compared to the cost of acquiring an expensive new conventional filtration system). And in South Portland’s highly developed Maine Mall area, several green infrastructure projects have been installed such as bioswales and porous pavement to manage stormwater.
Several case studies have highlighted the cost-savings of natural vs manmade infrastructure, including the New York Staten Island Bluebelt project where stormwater is controlled using existing natural drainage systems, e.g., streams, ponds, and wetlands in combination with other “green infrastructure” projects. An initial benefit-cost study found that the project would save more than $30 million over a conventional sewer-line approach. The Bluebelt includes about 400 acres of freshwater wetland and riparian stream habitat and almost 11 miles of stream corridor. According to a study by the Institute for Sustainable Design, it has successfully resolved regular flooding issues from southeastern Staten Island, while saving New York City an estimated $300 million in storm sewer construction costs.
The life span of a healthy wetland can also be significantly longer than that of man-made infrastructure, so the cost of each type of solution needs to be weighed in relation to their life expectancy and maintenance. Unlike a concrete structure, a successful natural infrastructure project will most likely not depreciate, and in fact, may actually increase in value over time. And they produce many ancillary benefits such as wildlife habitat, carbon sequestration, water filtration, groundwater storage and floodwater attenuation. However, an either-or situation is not the answer. Wetlands and natural infrastructure alone cannot support the needs of an ever growing human population. Finding new ways to use both approaches in concert with each other through integrated water management strategies will most likely provide the best results.
Useful Publications & Resources
- Natural Infrastructure: Investing in Forested Landscapes for Source Water Protection in the United States (World Resources Institute Report – 2013)
- Natural Infrastructure for Water (World Resources Institute webpage)
- Natural Infrastructure (USEPA website)
- Green Infrastructure (USEPA website)
- Low Impact Development (USEPA website)
- An Assessment of the Economics of Natural and Built Infrastructure for Water Resources in Maine (Univ. of Southern Maine & New England Environmental Finance Center Report – 2013)
- Integrating Natural Infrastructure Into Urban Coastal Resilience (The Nature Conservancy Report – 2013)
- Arizona Natural Infrastructure Data Sources (Center for Science & Public Policy and The Nature Conservancy – website)
- Green Infrastructure: Overview (American Society of Landscape Architects webpage)
- Landscape Performance Series Case Study Briefs (Landscape Architecture Foundation
- Integrating the Built and Natural Environment (Urban Greenspaces Institute webpage)