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M. E. Ikehara

Publications and source records attributed to M. E. Ikehara.

6 recordsLinked to original sources
USGS2000

Delta subsidence in California: The sinking heart of the state

The Sacramento-San Joaquin River Delta of California once was a great tidal freshwater marsh blanketed by peat and peaty alluvium. Beginning in the late 1800s, levees were built along the stream channels, and the land thus protected from flooding was drained, cleared, and planted. Although the Delta is now an exceptionally rich agricultural area (over a $500 million crop value in 1993), its unique value is as a source of freshwater for the rest of the State. It is the heart of a massive north-to-south waterdelivery system. Much of this water is pumped southward for use in the San Joaquin Valley and elsewhere in central and southern California. The leveed tracts and islands help to protect water-export facilities in the southern Delta from saltwater intrusion by displacing water and maintaining favorable freshwater gradients. However, ongoing subsidence behind the levees reduces levee stability and, thus, threatens to degrade water quality in the massive north-to-south water-transfer system.

California↗
USGS1995

Data from the Woodland land-subsidence monitoring station, Yolo County, California, water years 1988-92

A land-subsidence monitoring study was initiated in 1985 for the purpose of collecting data in Sacramento Valley, California, to document land-surface subsidence and to measure sediment compaction in response to ground-water pumping. Lithologic and geophysical logs obtained from the deeper of two boreholes drilled in 1987 near Woodland, California, are presented. The results of geotechnical and hydraulic laboratory tests on four sediment core samples extracted at 137, 151, 301, and 474 feet below land surface from a third borehole, drilled in 1990, are also reported. Construction of the extensometer well and the piezometer wells and equipment installed in the boreholes are described and illustrated. Data measured or recorded at the Woodland land- subsidence monitoring station from December 1987 through September 1992 are presented in tabular and graphic formats. These data include water levels from five piezometers, barometric pressure, and cumulative net sediment compaction.

Open-File Report↗
USGS1988

Determination of bench-mark elevations at Bethel Island and vicinity, Contra Costa and San Joaquin counties, California, 1987

Elevations of 49 bench marks in the southwestern part of the Sacramento-San Joaquin River Delta were determined during October and November 1987. A total of 58 miles of level lines were run in the vicinity of Bethel Island and the community of Discovery Bay. The datum of these surveys is based on a National Geodetic Survey bench mark T934 situated on bedrock 10.5 mi east of Mount Diablo and near Marsh Creek Reservoir. The accuracy of these levels, based on National Geodetic Survey standards, was of first, second, and third order, depending on the various segments surveyed. Several bench marks were noted as possibly being stable, but most show evidence of instability. (USGS)

Open-File Report↗