Model-grid and hydraulic-property data arrays of the MULT package of the Central Valley Hydrologic Model

This digital dataset defines the model-grid and hydraulic-property data arrays of the Multiplier (MULT) 
Package used in the transient hydrologic model of the Central Valley flow system.  The MULT package 
defines multiplier arrays for calculation of model-layer characteristics from parameter values. 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 simulation 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 than 50 percent of the cells are active. It 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 MULT Package includes the percentage of coarse-grained deposits in each of 
the 10 model layers, specific yield, and the altitudes of the tops of model layers 1-4.  In order to better 
characterize the aquifer-system deposits, lithologic data from approximately 8,500 drillers' logs of boreholes 
ranging in depth from 12 to 3,000 feet below land surface were compiled and analyzed. The percentage of 
coarse-grained sediment, or texture, then was computed for each 50-foot depth interval of the drillers' logs. 
A 3-dimensional texture model was developed by interpolating the percentage of coarse-grained deposits 
onto a 1-mile spatial grid at 50-foot depth intervals from land surface to 2,800 feet below land surface. The 
specific yield data were extrapolated from the percentage of coarse-grained deposits in model layer 1. 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