Hydrogeological study and modeling of the Kern Water Bank
The Kern Water Bank (KWB) is located in the Kern River alluvial fan at the southern end of the San Joaquin Valley, Kern County, California. In January and August 2000, shallow and deep monitoring wells were sampled at 10 or 13 locations, respectively. The samples were analyzed for chlorofluorocarbons (CFC-11 and CFC-12) and stable isotopes of water ([symbol omitted]18O and [symbol omitted]D). Results indicate that relatively young groundwater (40 yrs) are found in the southern and western areas and in the deep northern wells. The stable isotope composition varied significantly within the KWB and correlated neither with location or CFC age. It suggests a Sierra Nevada water source.
A numerical model of flow was developed using Visual Modflow Software. The model is composed of three layers (total thickness 226 m), representing the basic aquifer structure. Each layer is built on a 58 columns, 39 rows grid consisting of 1935 active and 327 inactive cells ranging in size from 0.16 to 0.65 km2. The model is built with hydrogeological parameters compiled by the California Department of Water Resources, monitoring wells, production wells, and assumed boundary conditions. Other field data consisted of: (i) spring 1994 initial groundwater surface, (ii) KWB and Kern County Water Agency (1994-2000) artificial recharge rates, (iii) seven years of hydraulic heads records at 26 monitoring wells and (iv) pumping rates at productions wells. The calibrated model was run over a 7 years simulation period (1994-2000) in a transient mode, with twelve time steps for each stress period. The root mean squared error between simulated and measured hydraulic heads was calculated at 8 m. The best agreement between simulated and observed hydraulic heads was found in the deep wells located in the southern section of the KWB away from the active spreading ponds.