Groundwater Management

While Turlock Irrigation District has no authority to regulate groundwater use, TID is 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 subunit of the larger San Joaquin Valley Groundwater Basin.

Conjuctive Use: balancing surface water and groundwater

The District utilizes a combination of surface water and groundwater to supply irrigation water to its growers. In dry years, groundwater pumping helps meet irrigation demand that cannot be supplied by surface water. In normal and wetter years, surface water makes up the bulk of the supply with groundwater being drawn upon to a lesser extent. 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 water is stored and then becomes part of the District's water supply in dry years. Groundwater is also the source of municipal water for Turlock, Ceres, South Modesto, 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 water.

The District's 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

TID has long been a leader in the management of local groundwater resources. The District first developed a groundwater model to predict the behavior of the underground aquifer under a variety of conditions over twenty-five years ago. Since that time, TID has continued to update and improve its model. 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.

The District has also taken an active role in local groundwater management and planning. The District has a long-standing program of groundwater level monitoring throughout its boundaries, and cooperates with other state and local entities to monitor the larger basin area. TID was the first local entity to adopt a Groundwater Management Plan in 1993, and is a member of the Turlock Groundwater Basin Association (TGBA), which has collaborated 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.