Central Valley Hydrologic Model:Introduction

Components of the Central Valley Hydrologic Model

Geospatial Database

A comprehensive geospatial database was developed using a Geographic Information System (GIS) to compile, manage, store, and analyze the large quantities of data needed to run the model, and to understand and visualize the data output.

Texture Model

A geologic texture model was developed to characterize the coarseness of valley-fill materials that make up the aquifer system. Lithologic data from approximately 8,500 drillers’ logs of boreholes ranging in depth from 12 to 3,000 feet below land surface, along with other information, were compiled and analyzed. The resulting geologic model was then used to estimate hydraulic properties for every cell in the model. The texture model is key to understanding how water moves through the Central Valley groundwater system.

Farm Process

The complex hydrologic system of the Central Valley is simulated by using the USGS hydrologic model, MODFLOW. Combined with the Farm Process, MODFLOW provides a tool to simulate natural and human-induced water movement and consumption over the landscape. Groundwater and surface-water flow are fully coupled. The model accounts for supply-constrained and demand-driven conjunctive use of water in agricultural, urban, and natural settings. In the Central Valley, the tool simulates unmetered historical pumpage and the delivery of surface water for 21 water-balance regions for water years 1962 to 2003.

Numerical Model

A numerical groundwater-flow model capable of being accurate at scales relevant to water-management decisions was developed for the Central Valley, California.