Simulation of Regional Groundwater Flow in Semi-Arid Farm

Abstract

A mathematical groundwater flow model is developed for drought affected semi-arid farm located in southern San Joaquin Valley, California. The objective was to simulate the flow direction and capture the potential recharge areas for water stressed crops. A finite difference grid of 20 rows and 35 columns was spaced with 700 active cells in X and Y directions and five layers in Z direction. The boundary conditions were selected from the USGS topographic map. MODFLOW-2000 integrated in Groundwater Modeling Software (GMS) was used to simulate 3-D flow. There are five observational wells in the study area monitored by California Water Science Center (CAWSC) and California Department of Water Resources (DWR). Available meteorological, geological and hydro-geological data were used to characterize the existing groundwater conditions and to simulate the equi-potential surface. The model was calibrated using groundwater elevation data against the historical water level data under steady-state conditions. A transient simulation was carried out from the year 2006 to 2011 for 5 stress periods. Results showed that the groundwater flows from west to east of the study area towards the California Aquaduct causing the drop in water table in the wells at the study area. The average water surface elevation (WSE) in 1950 for the growing season (May to July) was 161.04 m. This value is low when compared to those of 2009, 2010, and 2011, which are 237.14, 236.28, and 235.74 m respectively.

Keywords.  MODFLOW, GMS, finite difference, hydrogeology, modeling, recharge.