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Eastern San Joaquin Groundwater Basin Groundwater Management Plan undertaken. From a water resources planning perspective, the demands presented are sufficient. 2.6 Water Supplies The California water rights system, considered a dual system, recognizes both riparian and appropriative rights. Appropriative rights date back to the mid-1800's during the California Gold Rush under the "First-in-Time, First-in-Right' doctrine. The Water Commission Act of 1913 required that a permit be issued for appropriation of surface water and that the right be assigned a priority based on the date issued. Today, the SWRCB is the regulatory agency through which surface water rights are appropriated. Water rights acquired prior to December 14, 1914 are not subject to State Board regulation; however, Article X, § 2 of the California Constitution mandates that water must be put to "...reasonable and beneficial use..." or risk loss of water right. (http://ceres.ca.gov/, 2003) The State defines groundwater as either the underflow of a surface stream, a definite underground stream, or percolating waters. The appropriative water rights system applies to the first two definitions, but does not apply to percolating waters. Percolating waters are treated similarly to riparian water rights in that groundwater may be put to beneficial use in an amount proportional to the size and needs of the property. Only relatively recently have local public agencies and the State begun to look at the management of groundwater to prevent excessive overdraft. Disputes in groundwater rights have created adjudications in some basins whereby groundwater is extracted by court order. 2.6.1 Surface Water Supplies Water supplies in San Joaquin County are subject to the complex system of riparian and appropriative rights and are further complicated by numerous agreements and water service contracts. Table 2-6 provides a synopsis of the major water rights and contracts held by San Joaquin County water agencies. It is estimated that San Joaquin County has approximately 1.2 million of/yr of surface water available. This amount includes approximately 500,000 of/yr applied by farmers in the Delta. The actual quantity of water delivered varies significantly from year to year due to contractual and water right conditions. The actual quantities utilized within San Joaquin County also vary significantly with climatic fluctuations, infrastructure limitations, and facility operation. For example, although SEWD has an interim contract with USBR for 75,000 of/yr from New Melones Reservoir, this full quantity has yet to be made available to SEWD. Surface water supplies are likely to decrease in the future. As shown in Table 2-6, there are several current contracts for"interim" supplies, which are available subject to requirements of upstream or senior rights holders. As development increases in areas with senior water rights, San Joaquin County's surface water supplies will be reduced. 2.6.2 Groundwater Supplies Groundwater pumping quantities in San Joaquin County are not recorded at the water district or county level. Consequently, an accurate assessment of the quantity of groundwater used is difficult to establish. The approach adopted by DWR and other agencies to estimate groundwater withdrawals is based on land use and population. Using a similar approach with groundwater modeling, CDM estimated that the total agricultural and municipal groundwater pumping in Eastern San Joaquin County has averaged approximately 870,000 of/yr for the last 20 to 30 years. Sustaining the current rate of groundwater pumping in Eastern San Joaquin Northeastern San Joaquin County Section 2 Groundwater Banking Authority 77 Hydrogeology