A Five-Year Estimation of Wasted Potable Landscape Irrigation Water, Orange Crest-Mission Grove Area (OCMGA), Riverside CA

A potential large-scale field lab has been identified within the fully-developed Orange Crest/Mission Grove area (OCMGA) of Riverside CA that can be used to verify the efficacy of residential landscape water-saving devices. Anthropogenic (potable) surface water runoff rates of forty radially-oriented drainages were annually estimated from 2008 to 2012. Visual estimates were conducted during the afternoon hours during each July to reduce the influence of morning mass-residential landscape irrigation and each preceding rainy season, to collect daily surface water “base flow” data. The OCMGA is underlain by a relatively thin veneer of alluvium overlying shallow crystalline bedrock, into which two main paleodrainages underlying ~116 AC had been eroded. This presentation focuses on the two paleodrainages and their terminal drainages.

Instead of percolating downward to an underlying regional aquifer, the runoff is directed laterally outward via the paleodrainages as surface water. Thus, with proper instrumentation, this ideal hydrogeologic setting would allow one paleodrainage area to be used to en masse test the effectiveness of emerging water-saving devices and the other area to be used as a 2005-buildout “control”, by comparing before/after drainage runoff volumes.

Assuming that OCMGA landscape irrigation occurs 365 days/year, the combined runoff volumes from these drainages for 2008/2009/2010/2011/2012 were approximately 32/40/48/48/40 AFY. These volumes correspond to (state-wide) 2008/2009 drought conditions, a 2010/2011 increase in precipitation, and a 2012 decrease in precipitation. Thus, the averaged 2008/2009/2012 volume of 37 AFY from only ~116 AC may represent the “base flow” OCMGA runoff landscape irrigation volume, equivalent to the annual needs of 74 households. Using all OCMGA drainage volume data and assuming that the OCMGA represents typical irrigation practices/devices, extrapolation using 2010 California Department of Finance census data indicates that approximately 67,739 AF of potable water may annually be lost to landscape over-irrigation within southern California