Locations of hydraulic-head observations (HOBS) for the Central Valley Hydrologic Model (CVHM)

This digital dataset defines the well locations for hydraulic-head observations used in the calibration of the transient 
hydrologic model of the Central Valley flow system. The Central Valley encompasses an approximate 50,000 
square-kilometer region of California. The complex hydrologic system of the Central Valley is simulated using 
the USGSs numerical modeling code MODFLOW-FMP (Schmid and others, 2006).  This application is referred 
to here as the Central Valley Hydrologic Model (CVHM) (Faunt, 2009). Utilizing MODFLOW-FMP, the CVHM 
simulates groundwater and surface-water flow, irrigated agriculture, land subsidence, and other key processes 
in the Central Valley on a monthly basis from 1961-2003.  The USGS and DWR maintain databases of key wells 
in the Central Valley that are web-accessible (http://waterdata.usgs.gov and http://www.water.ca.gov/waterdatalibrary/, 
respectively). These data were combined to form a database of available water levels throughout the Central Valley 
from 1961 to 2003. More than 850,000 water-level altitude measurements from more than 21,400 wells have been 
compiled by the USGS or DWR and have been entered into their respective databases. However, only a small 
proportion of these wells have both sufficient construction information to determine the well-perforation interval and 
water-level measurements for the simulation period. For model calibration, water-level altitude data were needed 
that were (1) distributed spatially (both geographically and vertically) throughout the Central Valley, from the 
valley trough to the foothills; (2) distributed temporally throughout the simulation period (1961-2003); and (3) 
available during both wet and dry climatic regimes. From the available wells records, a subset of comparison 
wells was selected on the basis of perforation depths, completeness of record, climatic intervals, and locations 
throughout the Central Valley. Water-level altitude observations (19,725) for 206 comparison wells were used as 
calibration targets during parameter estimation.  The CVHM is the most recent regional-scale model of the Central 
Valley developed by the U.S. Geological Survey (USGS).The CVHM was developed as part of the USGS Groundwater 
Resources Program (see "Foreword", Chapter A, page iii, for details).

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Organization: Department of the Interior