Covering about 1,530 square miles (979,200 acres), the Kings Basin (Basin) is in the southern part of the San Joaquin Valley groundwater basin in California's Central Valley. Both agricultural and municipal users are dependent on the Basin’s water supply. The Basin includes portions of Fresno, Kings and Tulare counties and large population centers such as Fresno and Clovis. Much of the region is developed for agriculture and a large variety of crops. Irrigated land covers close to 500,000 acres, and most crops need irrigation water during the dry season. Several water districts serve much of the land in the basin.
The Kings River is the Basin’s major source of surface water. The River, its tributaries, and sloughs are the lifeline of riverine-riparian habitat that links the Sierra Nevada Mountains to the foothills to the Valley floor. Pine Flat Reservoir, located in the nearby Sierra foothills, regulates the flow of the Kings River and provides storage, flood control, hydropower and recreational opportunities. The San Joaquin River also is an important source of surface water to the Basin. Entities with water entitlements from the Central Valley Project (CVP) Friant Division use the Friant-Kern Canal to send that water into the Basin.
The Basin features an extensive canal network measuring more than 1,000 miles. That system delivers water to farmland, groundwater recharge facilities and several surface water treatment facilities. The weirs, diversion structures, canals and recharge facilities are part of an interconnected physical and hydrologic system managed by a variety of local and regional water agencies.
These water agencies manage the available water supply through conjunctive use, which is the combined use of surface water and groundwater. Water demand exceeds the surface water supply, necessitating conjunctive use of surface and groundwater as a supply source.
Many surveys and studies show that groundwater supplies are declining within the Kings Basin. This condition, considered generally as overdraft, is created when more water is pumped out of the ground than is replenished by rainfall, runoff or recharge.
Factors that influence available groundwater supplies include wet or dry hydrology, the degree of groundwater pumping, and the availability of structures to hold excess water for recharge. The Department of Water Resources estimates that total Kings Basin groundwater in storage is about 93 million acre-feet to a depth of more than 1,000 feet. Over the past 50 years, the Basin has experienced roughly 6 million acre-feet of groundwater storage reduction.
Today, experts predict a decline in groundwater storage at a rate of more than 120,000 acre feet annually. (An acre foot equals 325,900 gallons, or enough water to cover a football field to a depth of one foot.) The three general characteristics which contribute to the overdraft condition are considered to be: 1) groundwater pumping to meet agricultural water demand when surface water diversions are inadequate to fully meet the crop water requirements; 2) high reliance on groundwater for all demands in much of the western parts of the Kings Basin; and 3) urban development and reliance on groundwater once lands are converted to urban use from agricultural uses.
Many communities and water agencies prepare groundwater management plans or cooperate in similar regional planning efforts. Those plans aim to maintain or improve the groundwater supply in a specific area, and may also be used to coordinate planning efforts within hydrologic regions.
The Kings Basin groundwater aquifer system is composed of well-defined layers that include sand, silt, clay, rock and gravel. Underground banks of water, or aquifers, are created when water collects in formations of porous material.
The Basin’s underground landscape has been shaped by centuries of glacial movement, periodic flooding, mountain erosion and more. The characteristics of an area dictate whether an aquifer is formed.
Some deposits, or alluvium, are highly permeable and allow rainfall, runoff or other water to soak into the ground. More dense deposits of silt and clay limit the downward flow of water and create confined spaces for it to settle.
One of the most dominant features in the Kings Basin is Corcoran Clay, also called E-clay, which ranges to a depth of 550 feet. This thick clay layer acts as a barrier between underground aquifers, and occupies much of the western portion of the basin.
Aquifers exist in varying layers and depths throughout the basin. Throughout the region, groundwater generally flows to the southwest.
A critical solution to groundwater overdraft is finding both land and available water to replenish the groundwater supply. Both the Kings and San Joaquin rivers connect to the Basin and serve as sources of recharge. However, additional replenishment through recharge projects is needed. Fortunately, it is possible to expand recharge programs within the Basin.
Several factors help determine whether land is suitable for recharge. Those include current land use, proximity to canals or a water delivery system, the ability of soil to absorb and hold water, and elevations allowing for downward flow into the aquifer. Extensive studies show that there is acreage within Kings Basin boundaries that could be developed for this purpose.
Some potential areas exist in the southern portion of Fresno County, generally west of Highway 41 and ranging toward the Kings/Tulare county lines. Existing canals also have enough capacity to carry additional water to potential recharge areas.
Water from several sources may be available for recharge, such as excess flood flows from the Kings River and San Joaquin River, and local runoff. Those flows occur when Pine Flat Reservoir or existing facilities cannot store or manage all of the water in the Kings River in wet years. It is critically important to increase surface storage facilities in order to capture and recharge such waters.
Groundwater is a major source of drinking and irrigation supply for the Kings Basin region. The San Joaquin Valley has become one of the State’s most rapidly growing areas. Continued population growth and changing cropping patterns place additional stress on local groundwater supplies in the Kings Basin. Land-use decisions that do not consider groundwater impacts are detrimental to the sustainability of the groundwater supply.
Groundwater within the Kings Basin is greatly influenced by land use and the direction of water flow. Both urban and agricultural uses have contributed to declines in groundwater elevation throughout the Basin.
In metropolitan Fresno, for example, years of pumping for urban use have depressed groundwater levels. The water table in some areas has dropped to between 140 and 160 feet. The Raisin City area, which lacks access to surface water supplies, has a pumped groundwater for irrigation. There, the water table has dropped to about 200 feet and also created a depression that draws in water from other areas.
Recharge programs have produced healthier groundwater conditions in some portions of the Kings Basin. In the Fresno County region around Fowler, Kingsburg and Parlier, groundwater supplies have benefited from a nearly century-old recharge program by the Consolidated Irrigation District. Yet, the effectiveness of local recharge programs can be diluted by activity in other parts of the basin. For example, groundwater flows in much of the basin are moving westerly, northerly and southerly into the cone of depression in the Raisin City area. The direction of those flows demonstrates the interconnected nature of the groundwater basin.
Under California law, local government manages and decides issues of land use. In the past, agencies could make independent judgments about land use and water supply. Today, a variety of laws require decision-makers to more fully review water supply when dealing with proposals for development. In addition, other laws are helping create a better picture and management system for California groundwater.
Local planning agencies are compelled to consider water availability for a new project under 1995’s SB 901. Two additional pieces of legislation, SB 610 and SB 221, are companion measures designed to improve coordination and collaborative planning between cities, counties and water suppliers. Both laws require authorities to demonstrate that adequate and reliable 20-year water supplies are available for any new development as well as existing water users. Urban Water Management Plans can provide the basis for those water assessments.
SB 610 applies to larger development projects or land use plans that are subject to the California Environmental Quality Act process. SB 221 covers approvals of subdivision maps with more than 500 units. Several new and existing laws create a framework for improving the outlook for groundwater. The Groundwater Management Act (AB 3030), which took effect in 1993, permitted certain local agencies to develop groundwater management plans. Acting as water replenishment districts, those agencies can exercise greater management control over groundwater resources.
Amendments to the state’s Water Code in 2002 created more incentive for agencies to complete those documents, commonly known as AB 3030 plans. SB 1938 requires agencies to prepare and implement groundwater management plans to remain eligible for funding administered by the Department of Water Resources for groundwater or groundwater quality projects.
In 2009, the passage of SB X7-6 established a program tracking seasonal and long-range groundwater elevation trends in hundreds of California basins. Local monitoring agencies and the Department of Water Resources collaborate to collect and disseminate this data, which is publicly available through the California Statewide Groundwater Elevation Monitoring (CASGEM) database.
Finally, AB 359 requires local agencies to identify recharge areas in groundwater management plans in order to seek state funding for groundwater projects. The groundwater recharge maps also must be given to local land-use planning agencies as a tool in decision-making. However, the 2011 statute does not specify how the mapping should be completed or the type of information provided to planning agencies. Policies and Legislation on Land Use and Water Resources.