Groundwater & Surface water Modeling in the Walla Walla Basin
Starting in 2007, the WWBWC and Oregon State University (OSU) began work on a groundwater/surface water model for a portion of the Walla Walla Basin using the Integrated Water Flow Model (see below for more information on IWFM). The initial modeling efforts were focused in the orchard district northwest of Milton-Freewater using data from 2003-2006. As the WWBWC's monitoring network expanded, additional data were available to expand the model. Continuing the partnership with OSU, the model was expanded in 2012 to encompass most of the valley floor. This model was utlized to run a number of aquifer recharge scenarios and to develop a water budget for the groundwater/surface water system. Starting in 2014, the WWBWC and the Walla Walla Watershed Management Partnership initiated the Walla Walla Basin Integrated Flow Enhancement Study, which seeks to enhance stream flows while maintaining the long-term viability of water supplies for irrigated agriculture, residential, and urban use. As part of the study, the IWFM model was expanded to include the entire alluvial aquifer in the Walla Walla Valley. The WWBWC worked with GeoSystems Analysis, Inc. (GSA) on the model expansion and calibration. The expanded model will be used to run water management scenarios to meet established streamflow and water supply goals. The model will also be utilized to investigate aquifer recharge strategies and site placement. The model is an effective tool for evaluating the potential impacts of proposed water management scenarios on hydrological conditions in the basin.
What is Integrated Water Flow Model (IWFM)
IWFM (Integrated Water Flow Model) is a water resources management and planning model that simulates groundwater, surface water, stream-groundwater interaction, and other components of the hydrologic system. A unique feature of IWFM is the land use based approach of calculating water demand. IWFM simulates stream flow, soil moisture accounting in the root zone, flow in the vadose zone, groundwater flow, and stream-aquifer interaction. Agricultural and urban water demands can be pre-specified, or calculated internally based on different land use types. Water re-use is also modeled as well as tile drains and lakes or open water areas. Another notable feature of IWFM is a “zone budget” type of post-processor that includes subsurface flow computations across element faces. IWFM was developed by staff in the Modeling Support Branch of the Bay-Delta Office who is responsible for its technical support.
To learn more about IWFM please visit: http://baydeltaoffice.water.ca.gov/modeling/hydrology/IWFM/
Increased Aquifer Recharge Scenario
The animation below shows changes in groundwater levels at the end of a ten year scenario with increased aquifer recharge. Note levels are in meters.
Decreased Aquifer Recharge Scenario
The animation below shows changes in groundwater levels at the end of a ten year scenario with no aquifer recharge. Note levels are in meters.