Santa Maria River Valley

Source: CA DWR

Santa Maria River Valley


  • Basin Name
  • Santa Maria River Valley
  • Basin Number
  • 3-012
  • SGMA Basin Priority
  • High
  • Critically Overdrafted
  • No
  • Status
  • Adjudicated Basin
  • DWR Region & POC
  • Adjudicated Area Watermaster: Liese L. Schadt
    Luhdorff and Scalmanini, Consulting Engineers
    DWR contact for fringe areas:
    South Central Regional Office
    Matt Owens (559) 230-3335

  • Number of Wells
  • 1712
  • Hydrologic Region Name
  • Central Coast Hydrologic Region
  • Counties
  • San Luis Obispo, Santa Barbara


Located in California’s Central Coast hydrologic region, the Santa Maria River Valley is 184,072 acres in size. This High priority basin is home to an estimated 201,786 people (2010 value), which have been at a rate of 24.26. Santa Maria River Valley is a(n) basin with approximately 1712 wells, of which approximately 129 are water supply wells. Groundwater accounts for approximately 83.79 percent of the basin’s water supply.

Source: CA DWR
Source: CA DWR

Basin Notes

2003: Bulletin 118 basin description

2008: Eighty three per cent of the Santa Maria Valley Groundwater Basin’s 184,072 acres (or 162.036 acres) was adjudicated. Its management is now dictated by the courts.  The court action requires annual reporting which can be found on DWR’s Adjudicated Basins Annual Reporting System or on the City of Santa Maria’s website.

2018: DWR draft basin prioritization comment – Groundwater levels: elevations within the County section of the basin has declined in the range of 3.87 ft to 22.95 ft from 2005 through 2015. Source: 2012-2014_ASR FINAL.pdf 3) Groundwater levels in the deeper Squire Member of the Pismo Formation near Tri-Cities Mesa declined during the 1980s and partially recovered by 2000 to about 4 to 11 feet below late 1970s and early 1980s levels. Groundwater levels beneath Nipomo Mesa declined from 1 to 10 feet in the northern part during 1975 through 2000 and as much as 58.6 feet in the central part during 1968 through 2000; whereas water levels were stable in the western and southeastern parts, generally following rainfall cycles. Groundwater elevations within the County section of the basin has declined in the range of 3.87 ft to 22.95 ft from 2005 through 2015. Source: 2015 County of San Luis Obispo Sustainable Groundwater Proposal

Saltwater intrusion: Groundwater quality issues in the Santa Maria Valley Groundwater Basin include hardness, nitrates, salinity, sulfate and volatile organic compounds (DWR 2004al, 2013e; San Luis Obispo County 2011; SMVMA 2012). TDS concentrations are moderate to high. …Higher salinity levels occur in the shallow aquifer near the coast than within the inland areas or in the deep aquifer. Source: LTO-EIS_USBR_Chapter7-GWResources.pdf 2) Todd also assisted with the restoration of several coastal sentry wells and initiation of groundwater level and quality monitoring to provide an early warning system against seawater intrusion. Source: Santa Maria Basin Adjudication-Todd Groundwater_.pdf 3) The importation of State Water, which is generally of better quality than the local sources, provides for higher quality return flows and thus improves the basin water quality. In addition to improvements provided by the operations of Twitchell Reservoir and State Water importation, the Laguna Sanitation District helps to improve water quality in the basin by utilizing a reverse osmosis process to remove, and a deep injection well to dispose of, approximately 8,000 pounds of salts per day, which would otherwise accumulate in the basin system. With the deep injection system these salts stay far below the aquifer and are not a threat to return to the aquifer. …Salt Water Intrusion: Coastal monitoring wells are measured biannually for any indication of seawater intrusion; to date there has been no evidence of such. The concern of seawater intrusion is based on evidence that the Careaga Sand outcrops on the ocean floor several miles west and there are no Coast-Known barriers to seawater intrusion. Although it is possible that the seawater-fresh water interface has migrated shoreward during drought periods, the slope of groundwater has remained to the west in the westernmost part of the basin. Source: Santa Barbara County 2011 Groundwater Report

2018: Basin boundary modification request to subdivide the valley into two sub-basins pending before DWR.

GSA Information

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