Modeling the hydrologic and economic efficacy of stormwater utility credit programs for US single family residences.

As regulatory pressure to reduce the environmental impact of urban stormwater intensifies, US municipalities increasingly seek a dedicated source of funding for stormwater programs, such as a stormwater utility. In rare instances, single family residences are eligible for utility discounts for installing green infrastructure. This study examined the hydrologic and economic efficacy of four such programs at the parcel scale: Cleveland (OH), Portland (OR), Fort Myers (FL), and Lynchburg (VA). Simulations were performed to model the reduction in stormwater runoff by implementing bioretention on a typical residential property according to extant administrative rules. The EPA National Stormwater Calculator was used to perform pre- vs post-retrofit comparisons and to demonstrate its ease of use for possible use by other cities in utility planning. Although surface slope, soil type and infiltration rate, impervious area, and bioretention parameters were different across cities, our results suggest that modeled runoff volume was most sensitive to percent of total impervious area that drained to the bioretention cell, with soil type the next most important factor. Findings also indicate a persistent gap between the percentage of annual runoff reduced and the percentage of fee reduced.