The Sustainable Groundwater Management Act (SGMA) directs the Department of Water Resources (DWR) to identify groundwater basins and subbasins in conditions of critical overdraft. Conditions of critical overdraft result from undesirable impacts which can include seawater intrusion, land subsidence, groundwater depletion, and/or chronic lowering of groundwater levels. DWR identified such basins in Bulletin-118, 1980 and included the same area with the revised basin boundaries in Bulletin 118, Update 2003. As defined in the SGMA, “A basin is subject to critical overdraft when continuation of present water management practices would probably result in significant adverse overdraft-related environmental, social, or economic impacts.”
As required in the SGMA, all Bulletin 118 basins designated as high or medium priority and critically overdrafted shall be managed under a groundwater sustainability plan or coordinated groundwater sustainability plans by January 31, 2020. All other high and medium priority basins must be managed under a groundwater sustainability plan by January 31, 2022.
The Water Code outlines the following regarding basins subject to conditions of critical overdraft:
Water Code § 10720.7: PLANNING DEADLINES (a) (1) By January 31, 2020, all basins designated as high- or medium-priority basins by the department that have been designated in Bulletin 118, may be updated or revised on or before January 1, 2017, as basins that are subject to critical conditions of overdraft shall be managed under a groundwater sustainability plan or coordinated groundwater sustainability plans pursuant to this part.
Water Code § 10720.8: INAPPLICABILITY OF PART TO ADJUDICATED BASINS; REPORTING REQUIREMENTS FOR ENTITY ADMINISTERING ADJUDICATION (a) Except as provided in subdivision (e), this part does not apply to the following adjudicated areas or a local agency that conforms to the requirements of an adjudication of water rights for one of the following adjudicated areas.
Water Code § 12924: IDENTIFICATION OF GROUNDWATER BASINS The department shall also investigate existing general patterns of groundwater pumping extraction and groundwater recharge within those basins to the extent necessary to identify basins that are subject to critical conditions of overdraft. The final results will be published in the next update of Bulletin 118 expected in late 2016.
DWR identified a statewide base period of 1989 to 2009 for evaluation, which included wet and dry periods and has the same mean precipitation as the long-term mean. DWR also consulted with the State Climatologist to determine the base period. Groundwater elevation data available at DWR from the base period was very limited for many basins. DWR then conducted a review of available data, reports and other information to identify basins with obvious evidence of adverse impacts. DWR also utilized available groundwater elevation data and additional information from local agencies.
Groundwater conditions may have significantly worsened in some groundwater basins in the time since the last update of the list of critically overdrafted basins. A condition of overdraft during the current (2011 through 2015) drought period is not considered as an indication of overdraft, as the legislation requires the current drought period to be excluded from evaluation.
DWR developed a draft list of critically overdrafted basins that included 21 basins and subbasins. In July 2015, DWR notified the local basin managers and the counties with critically overdrafted basins. One or more undesirable impacts within a basin places the basin in critical overdraft. There may be additional critically-overdrafted basins, but DWR does not have sufficient data or information to determine that they are critically-overdrafted. The SGMA requires DWR to identify basins or subbasins rather than portions of basins or specific areas. Basins previously identified as critically-overdrafted on the Bulletin 118-1980 list have remained on the list unless agencies provided data documenting that the basins were no longer critically-overdrafted.
DWR presented the draft list to the California Water Commission (CWC) and the draft list was posted the on the CWC website on August 19, 2015. DWR conducted a public meeting and webcast on August 25, 2015, to discuss the draft results, explain background and process, and solicit public comment. The public comment period opened August 25, 2015 and closed on September 25, 2015.
Local agencies and interested parties had the opportunity to provide comments on the draft list of critically overdrafted basins. DWR evaluated the comments and data submitted. No revisions were made to the draft list. The final list will also be included in the Bulletin 118, Interim Update 2017, which is expected to be published in late 2016.
Click here to sign up to receive email updates on DWR SGMA activities. For additional information regarding the list of critically overdrafted basins, please contact Tim Ross, at Timothy.Ross@water.ca.gov or (818) 549-2345.