USE OF A NUMERICAL-MODEL FOR MANAGEMENT OF SHALLOW GROUNDWATER LEVELSIN THE YUMA, ARIZONA AREA

The Yuma area has experienced agricultural development since the late 1890s and ground-water levels have risen over 70 feet due to recharge from heavy application of irrigation water, unlined canals and floodin g along the Colorado and Gila Rivers, The resulting shallow water leve ls have seriously impacted residential areas and prime agricultural la nd. The Arizona Department of Water Resources in conjunction with Yuma County Flood Control District developed a regional three-dimensional ground-water flow model of the Yuma area, The purpose of the model is to assist local agencies in evaluating remedial water management alter natives to mitigate the shallow ground-water level problems. The model domain incorporates over 900 ml(-2) of Arizona, California, and Mexic o and simulates ground-water pumpage, deep percolation from agricultur al irrigation, evapotranspiration from phreatophytes and flow in 12 ca nals, 16 drains, and the Colorado and Gila Rivers, The model contains four layers with over 30,000 model cells ranging in size from 40 acres to 640 acres. Different model scenario simulations were conducted to evaluate the effectiveness of proposed water management alternatives o n lowering ground-water levels within the northern portion of Yuma Val ley, These scenarios include lining a portion of the East Main canal a nd pumping two drainage wells, lining the All-American canal, and simu lating a decrease in deep percolation from agricultural irrigation on the Yuma Mesa and northern portion of Yuma Valley.