Economic and Adaptation Benefits of Low Impact Development
This paper presents a range of case studies illustrating the advantages of Low Impact Development (LID) in economic terms and metrics employed in municipal decisions making. The environmental and water quality benefits of LID are commonly known however, there are also considerable economic, infrastructure, and climate adaptation benefits being overlooked or ignored. Municipalities are faced with difficult economic choices from reduced capital budgets and increasing regulatory demands. As such, there is value in understanding the substantive economic benefits—for both construction budgets and project life-cycle costs—that are increasingly being realized by municipalities, commercial developers, and others when using Green Infrastructure (GI) for stormwater management. LID is commonly misperceived as only adding expense to a project; however, this perspective fails to acknowledge the broader benefits that can be observed in terms of whole project costs for new construction, and in some instances, increased life-cycle benefits. While individually GI elements may add upfront capital expense to a project, reductions can result from a decreased need for conventional drainage infrastructure. Cost benefits are not observed in comparison with projects with few to no stormwater controls, but rather for projects consistent with new state and federal permitting requirements that address volume and pollutant reduction.
Studies examined reported cost reductions for LID designs when compared with typical designs that relied heavily upon the use of drainage infrastructure. Project cost reductions were observed from 6% in residential developments to as high as 26% in commercial projects. Municipal use of GI reported cost reductions of 21% to as high as 44%. Of significant importance is the shifting of monies from infrastructure to jobs associated with the maintenance activities. From a sustainability perspective, a range of benefits includes reductions in flood damage and increased resiliency of drainage infrastructure; as well as reductions of 33 to 50% in energy demands for heating and cooling. Additional benefits observed included a 50% reduction in time to sale, and increased property values of 12-16%. Other benefits were incentives in the form of rebates, cost- sharing, and tax credits.
The use of LID planning and structural controls can contribute to building community resiliency in managing water resources and reducing the flood risk associated with current and projected changes in land use and climate. In one study, the implementation of LID practices reduced the number of culverts determined to be undersized by 29 to 100 percent for the 24 hr - 25 yr event. The marginal cost increase to replace such undersized culverts was also reduced by one-third. At the site scale, the use of LID as an adaptation measure can increase onsite storage of runoff compensating for increases in rainfall depths due to climate change. Onsite storage has additional benefits that increase resiliency such as increases in lag time and reducing and delaying the runoff peak discharge. Minimizing 2-year to 100-year floods with LID has the benefit to minimize stream instabilities that result from hydromodifications.