Thesis 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.

Introduction

Watershed Background

The Walla Walla Watershed, which is shared by the states of Oregon and Washington, has gained public attention for its successful river restoration efforts in recent years.  Listed in 1998 as America’s 18th Most Endangered River, the Walla Walla River has seen successful changes occur in both the main stem that serves as a habitat for many endangered species, and in the restoration of water levels in the shallow aquifer gravel system on the Oregon side of the watershed.  With the collaboration of concerned groups, numerous studies have been funded in the area, and with the negotiation of irrigation districts, the watershed has been able to apply water resource management programs.

In the year 2000, two irrigation districts in Oregon, the Hudson Bay District Improvement Company and Walla Walla River Irrigation District, and one in Washington, Gardena Farms Irrigation District, agreed to leave 25 cfs (61x103 m3/d) in the Walla Walla River on the Oregon side and 18 cfs (44x103 m3/d) on the Washington side (WWBWC, 2002).  This program together with the discontinuation of gravel mining and the approval of the U.S. Army Corps of Engineers for construction of a levee by Milton-Freewater, OR and the Flood Control District, allowed for restoration of riparian vegetation and reduction of the temperature of the river.  Previously dry in the summer, today the Walla Walla River not only maintains flows throughout the year, but also creates aquatic habitats by restoration of the “natural” meandering of the river.

In 2004, on the Oregon side of the Walla Walla River Basin, the Walla Walla Basin Watershed Council (WWBWC), in partnership with the Hudson Bay District Improvement Company, created a pilot project to recharge the shallow aquifer by diverting water in the winter (November through May) from the irrigation canals into three man-made infiltration basins.  As a result of this restoration practice, aquifers levels have increased, making this pilot program a significant contributor to the optimization of regional water resources.  This recharge project not only maintains a stable flow in the old springs that drain into the Walla Walla River, but also helps the local economy by leaving more water in the aquifer that can be pumped for irrigation purposes, in the case of an increased demand, or used in the case of a drought season. 

A hydrologic simulation model for the Milton-Freewater region has been developed and calibrated using information gathered by the WWBWC since the year 2002 and other scientific research projects. This extensive work included the installation of monitoring wells, monitoring of irrigation canals and surfaces flows, installation and maintenance of climatic stations, determination of hydrogeology stratigraphy (Lindsay, 2003), land use coverage, and estimation of aquifer parameters  including hydraulic conductivity and porosity. 

Project Goals

In order to visualize the extended effects of water resource management projects and new potential scenarios, it is necessary to understand the interactions and functions of the processes involved in this complex hydrologic system.  Modern technological advances have made possible the development of a hydrologic model capable of simulating the interactions and processes between surface water and groundwater.  Results from the hydrologic model simulation will help in the decision making process by producing a water budget analysis and visualization of several management scenarios.  The model chosen for this project was the Integrated Water Flow Model (IWFM), developed by the California Department of Water Resources, given its strong conceptual and physically based method of simulating groundwater flow and its interactions with surface water, and utilizing a finite element method that makes it computationally efficient.  More information about the model is provided in section 2.2 IWFM History and Applications

Model Area
The model area (fig1) extends from the city of Milton-Freewater Oregon (Lon -118.42, Lat 45.962) to the state line with Washington. It is approximately 43.45 Km2 or 10,737.19 acres. For model development the area has been divided into 416 irregular elements, the normal area size for each element is 0.108 Km2 or 25.8 acres, the side of a regular quadrilateral element is 329 meters.

Down loads:

MS Thesis

Defense presentation

Presentation 16 June Watershed Council

People:

Walla Walla Basin Watershed Council (WWBWC)
Bob Bower
Troy Baker

OSU- Hydrologic Science Team (HST)
Richard Cuenca, PhD
John Selker, PhD
Arístides Petrides. petridea@onid.orst.edu

Other Links:

California Department of Water Resources
http://baydeltaoffice.water.ca.gov/modeling/hydrology/IGSM2/index.cfm

Walla Walla Basin Watershed Council
http://www.wwbwc.org/

OSU, Department of Bio-Engineering
http://www.bioe.orst.edu/

Hydrophiles, Oregon State University
http://oregonstate.edu/groups/hydro/

Hydrologic Science Team (HST)
http://bre.orst.edu/hst/