spreading ground

{{About|groundwater recharge facilities|the film produced in 2000|The Spreading Ground}}

File:Appendix to the Journals of the Senate and Assembly of the session of the Legislature of the State of California (1917) (14595351117).jpg

A spreading ground is a water conservation facility that retains surface water long enough for it to percolate into the soil. Spreading grounds must be located where underlying soils are permeable and connected to a target aquifer.{{cite web |url=http://dpw.lacounty.gov/wrd/SpreadingGround/ |title=spreading grounds |website=Public Works, Water Resources Division |publisher=Government of Los Angeles County}}

Locating them above silt or clay would prevent the surface water from reaching formations that store water.{{cite web |url=http://www.wrd.org/engineering/groundwater-replenishment-spreading-grounds.php |title=Groundwater Replenishment |website=Water Replenishment District of Southern California}}

When natural percolation of precipitation is insufficient to replenish groundwater withdrawn for human use, artificial recharge helps prevent aquifer depletion, subsidence and saltwater intrusion. Spreading grounds are one of several available technologies, and are useful to harness storm water runoff in populated areas with low annual precipitation.

For example, Los Angeles County, California has 27 such facilities, and four more operated in conjunction with the department{{huh|date=April 2023}}, many of which date to the 1930s.{{cite web |url=http://dpw.lacounty.gov/wrd/SpreadingGround/information/ |title=Spreading Facilities Owned and Operated by the Department |publisher=Government of Los Angeles County |accessdate=1 January 2015}}{{cite news|last1=Mozingo|first1=Joe|title=A behind-the-scenes battle to divert L.A.'s storm water from going to waste|url=http://www.latimes.com/local/california/la-me-storm-water-capture-20160311-story.html|accessdate=11 March 2016|work=Los Angeles Times|date=11 March 2016}}

While managed aquifer recharge (MAR) projects utilizing storm water and diverted surface water runoff augment groundwater recharge, data suggests that the infiltration capacity of spreading grounds in drought-prone regions is underused due to the seasonality of rainfall.County of Los Angeles Department of Public Works Water Resources Division. Hydrologic Report, 2013−2014; County of Los Angeles Department of Public Works: Los Angeles, 2015. In response, interest is being generated around MAR projects that utilize recycled water to supplement other water sources.Bradshaw, Jonathan L.; Luthy, Richard G. (2017-10-06). "Modeling and Optimization of Recycled Water Systems to Augment Urban Groundwater Recharge through Underutilized Stormwater Spreading Basins". Environmental Science & Technology. 51 (20): 11809–11819. doi:10.1021/acs.est.7b02671. ISSN 0013-936X. Orange County's Groundwater Replenishment System serves as an example of one such system that is combining recycled water and storm water to recharge groundwater through spreading grounds to meet the municipality's annual water needs.{{cite web | title=About GWRS | website=OCWD | url=https://www.ocwd.com/gwrs/about-gwrs/ | ref={{sfnref | OCWD}} | access-date=2022-03-23}}

Today, many spreading grounds, which were once considered single-purpose facilities, are being converted to combine municipalities' goals for groundwater recharge with demands for additional recreational opportunities, green space and wildlife habitat. The Dominguez Gap Wetlands in Long Beach, California, which consists of two spreading grounds, is an example of one of these multi-purpose facilities. While the facility's east basin was converted into constructed wetlands (Bixby Marshland (?)), the west basin remains a spreading ground that recharges the local aquifer by an estimated 450-acre feet annually.Landers J. Constructed Wetlands to Improve Los Angeles River's Water Quality. Civil Engineering (08857024) [serial online]. July 2008;78(7):31-33. Available from: GreenFILE, Ipswich, MA. Accessed June 1, 2018.