The Economic Water Model - a method and software program for assessing the impacts of storm water "green solutions" in urban areas

Abstract

A new model is needed for storm water "green solutions" such as rain gardens, bioswales, and rain barrels. Estimating average annual runoff at the property level is essential to providing precise estimates on the effectiveness of stormwater “green solutions� like rain barrels and rain gardens. This information can also be used to implement a more accurate stormwater fee so municipalities can generate revenue to fund water infrastructure improvements, water conservation efforts, or storm water mitigation projects, while also providing a performance based rebate for those property owners who do install a storm water green solution. Rather than use modeling tools that utilize single design storms and runoff coefficients, site-specific GIS data can be input for a continuous runoff model whose focus is not conveyance but interception and infiltration. A distributed, deterministic Economic Water Model (EWM) method and modeling software was developed to estimate runoff using site-specific climate, soil, slope, and surface conditions extracted from GIS, weather station, and USDA soil data. Findings indicate that widespread implementation of rain barrels and rain gardens can have significant effects on urban runoff, especially in dense residential areas with small lot sizes. While this model also demonstrates that energy consumption is reduced at the municipal level through reduced combined sewer water treatment, the most significant water-related energy savings is from simple water-saving devices like low-flow faucet aerators. The results of this modeling can be used to implement and maintain more sustainable water infrastructure systems, economically and environmentally.