A Rainwater Harvesting Accounting Tool for Water Supply Availability in Colorado

Abstract

Rainwater harvesting (RWH) is a renewable water supply option for nonpotable use, most commonly used for landscaping irrigation. Water rights in Colorado prohibit all RWH except residential rain barrels and a pilot project program that allows centralized rainwater harvesting for new development. Development of a natural catchment creates impervious surfaces, thereby increasing runoff, with a subsequent decrease in infiltration and losses to evapotranspiration; pilot projects are allowed to harvest a volume equal to the predevelopment runoff losses that would have occurred on new impervious areas at the site. To support this administrative policy, a tool was developed for the efficient calculation of daily allowable harvest at nearly any project site in Colorado. A reliable and useful policy tool requires the incorporation of hydrologic science with widely applicable, user-friendly design, a challenging balance of rigor and accessibility that is welcomed by engineers and policymakers alike. The daily allowable harvest is determined for each soil group as a percentage of infiltrated rainfall less the groundwater return. Horton's infiltration method is used to model rainfall-runoff for a range of soil parameters (NRCS hydrologic soil groups) and precipitation events (0.25-to 25-year return periods and 15-min to 24-h durations). For most events, the percent infiltration is 90% of the precipitation depth; this ratio decreases when precipitation exceeds the infiltration rate. Results are simplified in a spreadsheet tool for policy application, with allowable harvest rules binned by event duration and frequency. Simulations using the tool for a 2010-2017 precipitation record from Colorado's Front Range showed that RWH can supply up to 50% of the annual demand for traditional landscaping and over 100% of the water-smart landscaping demand.

Scientometric Review of Smart Water Management Literature From the Sustainable Development Goal Perspective

“…Most studies tried to improve groundwater use efficiency using smart solutions (Fornarelli et al, 2022). The remaining 15 studies considered other ecosystems, such as wetlands (Mahdianpari et al, 2021), lakes (Maleki et al, 2022), mountains (Gilliom et al, 2019), and rivers (Kartakis et al, 2017).…”

Champions and Traditional Technocrats: The Role of Environmental Value Orientation in Stormwater Management

“…There is no green infrastructure requirement, although municipalities have strategies related to green infrastructure (City and County of Denver 2018). The City and County of Denver have drainage criteria that two-year storms (residential) to five-year storms (commercial and industrial) should be fully conveyed within pipes and dedicated drainage channels, but not all sewersheds are meeting these criteria (Gilliom et al 2019). Stormwater improvements in the City and County of Denver to meet these criteria are expected to cost $1.48 billion (The City and County of Denver Storm Drinage Master Plan 2014).…”

Urban stormwater characterization, control, and treatment

“…Because of these restrictions, a tool to calculate the daily allowable harvest was developed using soil parameters and precipitation data. Using simulations from 2010 to 2017 from the Colorado Front Range, researchers concluded that rainwater harvesting can supply up to 50 percent of the annual demand for traditional landscaping irrigation water (Gilliom, Bell, Hogue, & McCray, 2019). Another study looked at simulations of rainwater harvesting and the capability of short-term rainfall data to produce accurate long-term predictions (Soares Geraldi & Enedir, 2019).…”