Modeling surface water and groundwater interactions near Milton- Freewater, Oregon

Abstract

The gravel aquifer of the Oregon side of Walla Walla River Basin has a strong hydrologic connection to surface water through a series of springs, unlined irrigation canals, the Walla Walla River, numerous wells and, since 2004, artificial recharge to the shallow aquifer using infiltration basins. The finite element Integrated Water Flow Model (IWFM) developed by California Department of Water Resources was used to quantify all of the major hydrologic features of the basin. Using the information provided by the Walla Walla Basin Watershed Council, irrigation districts, and previous studies conducted at Oregon State University and by consultants, the model was setup and calibrated, and a water budget simulation was performed for the years of 2003 to 2006. It is shown that close to 96 percent of the land use water demand goes to agriculture growing 16 major crops. 60 percent of the water comes from surface water diversions flowing through unlined irrigation canals , which themselves lose 28 percent of their inflow to the unconfined gravel aquifer. The calibrated and validated model was used to simulate the flow of the Johnson Creek Springs, which were shown to have increased flow due to the artificial recharge project.