Abstract
Urban stormwater is increasingly being considered a viable alternative water supply in California and throughout the southwestern U.S. However, current economic analyses of stormwater capture do not adequately examine differences in stormwater project types and do not evaluate co-benefits provided by the projects. As a result, urban stormwater capture is undervalued as a water supply option. To advance economic analyses of stormwater capture, we determined the levelized cost of water in U.S. dollar per acre-foot of water supply (AF; 1 AF = 1233.5 m3) for 50 proposed stormwater capture projects in California, characterizing the projects by water source, process, and water supply yield. In addition, we incorporated reported co-benefits of projects into the analysis to determine the net benefit of proposed projects. Proposed urban stormwater capture projects were more expensive than non-urban stormwater capture projects on a per-volume basis ($1,180 per AF and $531 per AF, respectively); however, this was primarily driven by the relatively large size of the non-urban stormwater capture projects examined. When incorporating the limited number of reported co-benefits of the projects, the expected levelized cost of water from urban stormwater capture projects decreased dramatically. For projects that reported even a limited number of additional benefits, the net levelized cost decreased from $1,030 per AF to $150 per AF, with some of the projects demonstrating a net benefit. Thus, scaling urban stormwater capture projects to capitalize on economies of scale and incorporating co-benefits of projects can dramatically improve the economic feasibility of these projects. This work demonstrates that stormwater capture can present a cost-effective water supply option in California, and that beyond California, fairer comparisons among projects and inclusion of co-benefits can provide decision makers with adequate information to maximize investments in water management.
Highlights
In urban areas, precipitation and excess irrigation that falls on impermeable or semi-permeable surfaces, such as roofs or roads, can run off into nearby channels and waterways, carrying oils, heavy metals, soil, salts, and other pollutants with it
The selected projects were located in eight different Department of Water Resources (DWR) hydrologic regions, but concentrated in the South Coast region of California, where 32 of the 50 stormwater capture projects and 19 or 27 urban stormwater capture projects were proposed (Fig 2)
Projects varied by 3 orders of magnitude in their total stormwater water supply yield, ranging from 1.53 to 17,400 acre-feet per year (AFY), with a median of 552 AFY (Table 2)
Summary
Precipitation and excess irrigation that falls on impermeable or semi-permeable surfaces, such as roofs or roads, can run off into nearby channels and waterways, carrying oils, heavy metals, soil, salts, and other pollutants with it. This water, commonly referred to as urban stormwater, has historically been managed to mitigate flooding and surface water. An additional shift is occurring within stormwater management: with growing pressure on water supplies, communities in California and the southwestern U.S are expanding stormwater management to include investment in stormwater capture as a means of augmenting water supplies. In 2011, the City of Los Angeles passed a low-impact development (LID) ordinance requiring stormwater runoff to be captured on-site to increase groundwater recharge and offset imported water needs [5]
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