Location of General Head Boundaries (GHB) in the Central Valley Hydrologic Model (CVHM)

This digital dataset represents the area where lateral flow into and out of the Central Valley groundwater-flow system occurs.
The General Head Boundary (GHB) is set to 0 and is only in the Delta and is specified in layer 1 where the groundwater
system intersects the surface water 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 USGS 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 total
active modeled area is 20,334 square-miles on a finite-difference grid comprising 441 rows and 98 columns. Slightly less
that 50 percent of the cells are active. The CVHM grid has a uniform horizontal discretization of 1x1 square mile and is
oriented parallel to the valley axis, 34 degrees west of north (Faunt, 2009). 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).