Groundwater Management

While we have no authority to regulate groundwater use, we are a leader in regional groundwater stewardship because groundwater is such a cherished resource. Groundwater within the District is supplied by the Turlock Groundwater Basin, which is a sub-unit of the larger San Joaquin Valley Groundwater Basin.

Conjunctive Use: balancing surface water and groundwater

We utilize a combination of surface and groundwater to supply our growers. Growers utilizing flood irrigation contribute to the replenishment of the groundwater supply by allowing water to soak into the ground where a portion of it eventually reaches the underground aquifer. In normal and wetter years, surface water makes up the bulk of the supply with groundwater being drawn upon to a lesser extent. In those years, growers using flood irrigation are net groundwater rechargers, providing more water to the aquifer than is pumped out.  In dry years, this stored groundwater can be utilized to help meet irrigation demand that cannot be supplied by surface water alone. This practice of utilizing surface and ground water to meet local requirements is known as conjunctive use.

The District’s conjunctive use strategy is vital to maintaining a stable water supply. Deep percolation of surface water past the root zone is the primary method of groundwater recharge in the Turlock Groundwater Basin. This stored water then becomes part of the District’s water supply in dry years as well as being the sole source of drinking and municipal water for Turlock, Ceres, Hilmar, Hickman, Hughson, Denair, Delhi, Keyes, Ballico, and rural residences in the Turlock Groundwater Basin. Agricultural areas extending from the eastern boundary of TID to the Sierra Nevada foothills also rely exclusively upon groundwater for irrigation needs.

Simple diagram of Conjunctive Use

Our use of groundwater also plays an important role in water conservation. TID-owned and -rented pumps (distributed throughout the District) not only provide an additional source of water, they are used to help control flow fluctuations in the canal system. This helps TID Water Distribution Operators conserve water by reducing spills at the end of the canal system.

Groundwater Leadership

We’ve long been a leader in the management of local groundwater resources developing a model to predict the behavior of the underground aquifer under a variety of conditions over twenty-five years ago and since that time, we’ve continued to update and improve it. The model has proved to be a useful tool for evaluating the potential future impacts of land use changes, the sustainability of groundwater supplies, and drought planning efforts.

We’ve also taken an active role in local groundwater management and planning through our long-standing program of monitoring groundwater levels inside our boundaries, and cooperating with other state and local entities to monitor the larger basin area. We were the first local entity to adopt a Groundwater Management Plan in 1993, and are a member of the Turlock Groundwater Basin Association (TGBA), collaborating on groundwater issues since 1995. The TGBA developed basin-wide Groundwater Management Plans in 1997 and January 2008. The TID Board of Directors adopted the latest Groundwater Management Plan on March 18, 2008.

The Sustainable Groundwater Management Act (SGMA)

The Sustainable Groundwater Management Act (SGMA) was signed into law by Governor Brown on September 16, 2014 and became effective on January 1, 2015 enabling local agencies to manage groundwater so long as specific actions are taken and timelines met.

SGMA required local agencies form a Groundwater Sustainability Agency (GSA) or multiple GSAs, covering the entire Turlock Subbasin by June 30, 2017. GSAs are required to develop and implement a Groundwater Sustainability Plan (GSP) or plans to achieve sustainability and prevent “undesirable results.” This plan must be completed by 2022 and sustainability achieved by 2042. Under SGMA, failure to comply with any of these requirements may lead to state intervention in which case the State Water Resources Control Board (SWRCB) would require reporting, charge fees and may create interim management plans until such time that local agencies are able to take over.

Two GSAs formed within the Turlock Subbasin in 2017.

  1. The West Turlock Subbasin Groundwater Sustainability Agency (WTS GSA) which is encompassed nearly completely by the TID service territory and includes the cities of Turlock, Ceres, Hughson, Modesto and local water districts as well as the counties of Stanislaus and Merced, TID, and several other public water agencies.
  2. The East Turlock Subbasin Groundwater Sustainability Agency (ETS GSA) which is made up of the white area east of TID. The boundary separating the two GSAs is generally the Turlock Irrigation District’s eastern irrigation service area boundary.

For more information on SGMA compliance within the Turlock Subbasin, please visit

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