Spokane Valley-Rathdrum Prairie Aquifer Study

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Idaho and Washington agree on water management protocols

The Idaho Department of Water Resources (IDWR) and the Washington Department of Ecology (Ecology) have an agreement that guides how the two states will continue to coordinate with each other about water supply issues in the Rathdrum Prairie-Spokane Valley aquifer.

IDWR and Ecology’s water resources programs administer water rights and make determinations about water availability in their respective states.  The aquifer serves more than 500,000 residents in portions of Spokane County, Washington and Bonner and Kootenai counties in Idaho.

The agreement details the continued coordination involving the maintenance and improvement of the technical tools developed in a bi-state water study.  The computer model is capable of allowing water managers to enter data about a proposed withdrawal and see just how it would affect water levels in the vicinity of the withdrawal.  With this tool water managers from both states can make well informed decisions about water allocation

The Memorandum of Agreement establishes a collaborative “modeling committee” of experts from both sides of the border to manage and secure the computer model and make sure that any updates are agreed upon by both states.  The committee will decide what enhancements to the model would be valuable and establish the direction in which research should go to enhance the model.

The agreement was signed by IDWR Director David Tuthill, and Ecology Director Jay Manning.

The committee will establish protocols to make sure that the most recent version of the model is available to local government and the general public.  Meeting minutes, schedules, and materials relevant to the model and committee process will be posted to the Spokane Valley-Rathdrum Prairie Modeling Committee web page.

“This agreement frames a process for the continuation of the excellent Washington and Idaho cooperation in managing this important aquifer.  An additional benefit of the aquifer study has been the development of a close working relationship between Ecology and IDWR. It is important for those relationships to be built upon as we move forward with management decisions,” said David Tuthill, director of IDWR.

Project Information

Spokane Valley-Rathdrum Prairie Aquifer Study Results and Policy Summit

A study of the Spokane Valley-Rathdrum Prairie (SVRP) aquifer has been conducted jointly by Idaho Department of Water Resources (IDWR), U.S. Geological Survey (USGS), and the Washington State Department of Ecology.  Begun in 2003 with broad community support, the purpose of this project is to provide a scientific foundation for managing water in the SVRP aquifer.

The major product of the study is a numerical groundwater model that Washington and Idaho can use to cooperatively manage the SVRP aquifer and adjacent rivers and lakes.  Information gathered by partner agency scientists and contractors has expanded and refined our understanding of the aquifer and its interaction with local lakes and the Spokane and Little Spokane rivers, and water use region wide.

May 8-9, 2007 Study Results and Policy Summit

On May 8 and 9, 2007 three sessions were held at Mirabeau CenterPlace in the Spokane Valley.

On Tuesday May 8, the data, computer model, “water budget” and other technical information was described in detail.  That evening a general overview of what the study means to Spokane and Coeur d’Alene-area residents was presented and targeted to those who do not necessarily have a scientific background.

On Wednesday, May 9, elected officials and decision-makers from Idaho and Washington began discussing how the two states will work together into the future to share this precious resource and make sure it is plentiful for generations to come. 

Using the information gathered during the study, panels discussed the similarities between the two states; water law, local needs and general water issues. Many used this time to begin discussing the aquifer as a region-wide, shared resource that defies political boundaries.

The project has built an extensive body of publicly available information.  All this new information, building upon former studies (both local and region wide), is now incorporated into a numerical model of how water moves throughout the system. 

This model, a detailed mathematical representation of regional water movement over time, can be used to simulate responses of the system to stresses.  The states will be able to use this model to assess effects of new or changing patterns of use to existing water users or area lakes and rivers, and evaluate compliance with relevant state laws. 

In effect, the model provides a detailed, up-to-date basis for simulation of all aspects of ground water, from water rights decision making to establishing wellhead protection zones.  It provides the best available science for use by states, local government, and planning groups in regional and local water planning and zoning efforts.

Background of the Study

The study was funded by a combination of Congressional appropriations, state funding from both the Washington and Idaho legislatures and staff support from both state agencies.  Federal appropriations through the U.S. Environmental Protection Agency were divided equally between the states.  The total cost was approximately $3.5 million at the completion of the bulk of the study.

The project is the product of an extraordinary coalition of public entities, water purveyors, and non-governmental organizations.  This study provides the science upon which agencies and decision makers will rely when making local water-management decisions in the region.

Building upon previous work, the hydrogeology of the region has been completely reassessed.  The basin boundary is defined by the contact of relatively impermeable old rocks and the Quaternary glacial debris fill, deposited by a series of floods draining Missoula, Columbia, and Okanogan glacial lakes.  The boundary has been redrawn to reflect the latest information.  Incorporation of recently available geologic information has revealed significant complexity in the subsurface distribution of sediments. 

Recurring measurements of stream flow and groundwater levels during the project have given scientists the data needed to fine tune the model and better understand ground and surface water and their interaction. 

Using geophysical tools, project scientists have "looked" under the surface of the area.  The result is a new, detailed estimate of the shape of the basin.  That estimate is being confirmed by drill testing by project partners. 

Significant new information from this study refines earlier estimates of hydrologic information.  New estimates of the hydraulic properties of aquifer materials are available, provided by techniques monitoring aquifer response to regional hydrologic events.  Low and high stream flow measurements and temperature profiling using state of the art instrumentation have increased the precision of our understanding of how and where the aquifer and surface waters interact. 

Researchers used new ways to estimate recharge to the aquifer from the adjacent highlands and from precipitation on the valley floor.  Local entities, cooperating with project partners, provided an up-to-date dataset on regional water use.


Guy Gregory
Washington Department of Ecology
ERO Spokane, WA