SR0084717_SSNL - Laserfiche WebLink

Home Browse Search

GROUND WATER IN THE CENTRAL VALLEY, CALIFORNIA A7 that runoff in the valley is highly variable. Because of such high variability of both precipitation and runoff, early settlers soon learned that ground water was a more dependable source than surface water. PREVIOUS INVESTIGATIONS Because of the long history of ground-water develop- ment and its severe impacts, many hydrologic investiga- tions have been done in the Central Valley by the California Department of Water Resources, the U.S. Geological Survey, and various local agencies. The earli- est systematic study of California's water resources was by Hall (1886, 1889). Two important early studies were a summary of ground-water resources in the San Joaquin Valley by Mendenhall and others (1916) and a description of the geology and ground-water resources in the Sacra- mento Valley by Bryan (1923). These two studies were particularly useful in the investigations of the regional flow system described in chapter D of this series (Williamson and others, 1989) because they documented hydrologic conditions prior to large-scale irrigation de- velopment. In the early 1950's, the State of California and the U.S. Geological Survey cooperated in a series of ground-water reconnaissance studies that revealed nearly continuous annual declines of ground-water levels for large areas of the San Joaquin Valley and for some interstream areas of the Sacramento Valley. Two reports prepared during the 1950's provided summary descriptions of the ground- water hydrology of the San Joaquin Valley (Davis and others, 1959) and the Sacramento Valley (Olmsted and Davis, 1961). Comprehensive investigations of land subsidence in the San Joaquin Valley have been carried out since the 1950's by the U.S. Geological Survey under the direction of Joseph F. Poland. These landmark studies clearly show the relation between ground-water-level decline, com- paction of fine-grained sediments, and land subsidence. Land subsidence in the Central Valley was described in several reports by Bull (1972), Lofgren (1975), Bull and Miller (1975), Bull (1975), Bull and Poland (1975), Poland and others (1975), and Ireland and others (1984). The mechanics of compacting sediments were described by Meade (1964,1967, 1968), Riley (1970), Miller and others (1971), and Poland and Ireland (1988). A bibliography of nearly 600 reports that describe ground water in the Central Valley was compiled by Bertoldi (1979). WELL-NUMBERING SYSTEM Wells are identified according to their location in the rectangular system used for the subdivision of public lands. The identification consists of the township num- ber, north or south of a base line; the range number, east or west of a meridian; and the section number. A section is divided into sixteen 40-acre tracts lettered consecu- tively (excluding I and 0), beginning with A in the northeast corner of the section and progressing to R in the southeast corner (fig. 5). Within the 40-acre tract, wells are sequentially numbered in the order they are inventoried. The final letter refers to the base line and meridian relative to which the townships and ranges are numbered. For the Central Valley, this is the Mount Diablo base line and meridian (M). HYDROGEOLOGY The Central Valley is a long, narrow, northwest- trending, asymmetric structural trough that has been filled with about 32,000 ft of sediment in the southern part and as much as 50,000 ft in the northern part (Page, RANGE 1W 1E 2E 3E 11N SECTION 23 FIGURE 5. Well-numbering system.