Spokane Valley-Rathdrum Prairie Hydrologic Project

The Need for a Study

In 2001, two power companies applied for permits to divert a significant amount of groundwater (15 million gallons per day) in the Post Falls area. Their applications caused concern—especially related to the impacts that might occur to the lower Spokane River flows if the diversions were allowed. The permits were denied in 2002. However, their request put into motion the discussions about water use in the SVRP which ultimately led to the large-scale study that has taken place since.

Purpose & Objective

The project provided a scientific foundation for managing the SVRP aquifer. The key objective was the development of a numerical groundwater model that Washington and Idaho can use to cooperatively manage the SVRP aquifer and adjacent rivers and lakes. To accomplish this objective, a number of sub-objectives (such as aquifer characterization, hydrologic data collection, water usage, and groundwater-surface water interactions) were identified and have been addressed over the course of the study.

Scope of Work

In August 2003, a draft scope of work accompanied the appropriation request. The scope of work was based upon the assumption that the full requested appropriation would be forthcoming and that Washington and Idaho would contribute matching funds.

• Spokane Valley-Rathdrum Prairie Hydrologic Study Proposed Project Scope – July 7, 2003

Project Phase 1: Data Collection and Groundwater Modeling (2004–2008)

Work Plans

• FY2004 SVRP Project Work Plan
• FY2005 SVRP Project Work Plan

In Spring 2002, public meetings began with the purpose of discussing the future management of the water resources in the SVRP aquifer. Spurred on by the success of these meetings, Idaho’s US Senators secured $0.5 million in federal funding for the first phase of a regional aquifer study. Additional federal funding of $1.75 million and $0.15 million were provided in 2005 and 2007, respectively. Major accomplishments during this phase were:

• Geologic, hydrologic, and groundwater-flow information were compiled for Washington and Idaho. The study identified nine data needs, and most of these needs were addressed in later studies.
• A hydrogeologic framework and water budget were developed for the SVRP aquifer. The study identified three data needs, one of which became a major focus in Phase 2 (such as better estimates of seepage from Coeur d’Alene Lake and Lake Pend Oreille, and underflow from the aquifer into Long Lake).
• Monitoring wells were drilled during this time period (seven in Idaho), and both Washington and Idaho set up comprehensive groundwater monitoring networks.
• The groundwater-flow model was created and calibrated with existing groundwater-level data. The model results showed that simulated and modeled streamflow gains and losses and aquifer head were generally in agreement. The team recognized that the model had some uncertainties concerning the fluxes into the aquifer from Lake Coeur d’Alene and Pend Oreille.
• Spreadsheet tools were created to simulate various scenarios, and these indicated that withdrawals from Idaho and Washington will affect the streamflow in the Lower Spokane River in Washington.

Project Phase 2: Additional Technical Studies and the Inception of Thermal Modeling (2008–2010)

Coeur d’Alene Lake Water Budget
The USGS conducted a study on the water budget of Coeur d’Alene Lake for the time period from 2000–2005. The authors concluded that the difference between inflow and outflow values was less than one percent, and the amount of loss to the aquifer from the lake and the Spokane River was about four percent of the inflow.

• FY2010 SVRP Project Work Plan

Hydrogeologic Framework and Hydrologic Observations in the Coeur d’Alene to Post Falls area
Ralston Hydrologic Services, Inc. was contracted to complete two studies along the southern margin of the SVRP aquifer in Idaho.

• The first study focused on the hydrogeologic framework from the Idaho/Washington state line to Coeur d’Alene. Based on the work, Ralston recommended drilling several monitoring wells along the Spokane River from the Coeur d’Alene Lake outlet to Post Falls Dam in order to improve the understanding of leakage into the aquifer.
• The second study analyzed the groundwater elevations and water temperature relationships in the Coeur d’Alene Lake outlet area. The study concluded that, in general, groundwater levels are closely related to lake levels, although some anomalies in the degree of hydraulic connection were recognized.

Nimmer and Ralston (2008) used water temperature data from transducers deployed in wells on Blackwell Island to show that annual temperature fluctuations occurred in patterns similar to water level cycles. However, water temperature responses in individual wells were delayed with respect to the associated water level cycles, ranging from days to several months.

Thermal Data Collection and Modeling in the Farragut State Park to Athol area
The recognition that cyclic water temperature signatures occur in manners similar to water level cycles brought about the idea of using temperature as a tracer for modeling groundwater flow in the aquifer and, ultimately, for determining the flux from the lakes into the aquifer.

New Monitoring Well Construction along the Spokane River near Coeur d’Alene
In December 2010, two new monitoring wells were completed about 1.5 miles northwest of the Coeur d’Alene Lake Outlet. These wells are monitored for water levels and water temperatures in an effort to determine the hydrologic connection between the river and the aquifer in this area.

Current Status of Monitoring Network
With the addition of the two monitoring wells in the Coeur d’Alene area, the current monitoring network in Idaho consists of 28 wells. Most of the monitoring wells are unused and have pressure/temperature transducers deployed in them.

Project Phase 3: New Monitoring Well, Thermal Modeling, and Refined Monitoring (2011–current)

Additional technical work is needed to further refine estimates of flux from the two large lakes, and ultimately to improve the existing groundwater-flow model and spreadsheet tools in order to conduct more accurate aquifer stress simulations. Lack of funding is a major hurdle for this work.

Farragut Monitoring Well
The probable location for a new monitoring well is midway between the western end of Idlewild Bay and Farragut #5. The proposed well depth is 450 feet, extending about 100 feet into the aquifer. The well was drilled in Summer 2011.

Temperature Profiles at Farragut wells
IDWR conducted temperature profiles in several Farragut wells in March 2011 when water levels were at their lowest. These profiles provide additional information about water movement from the lake into the aquifer throughout the annual cycle.

Enhanced Thermal Monitoring
IDWR continues to assess monitoring data and make adjustments with the transducer placements, as necessary.

Thermal Modeling
Additional modeling was attempted using the HST3D and/or the MT3D models. Both are available for no cost to IDWR.

Well Deepening
As funding becomes available, the Highway 54 and Farragut #5 wells might be deepened 75 to 100 feet to collect more water temperature data.

Ongoing Data Collection
Monitoring wells with transducers are visited at least once per year for water level measurements and downloads. Wells without transducers are measured three or four times per year.

Reference Material for the Spokane Valley-Rathdrum Prairie Hydrologic Project

Technical Publications

• Groundwater Pumping Study – 2015
• SVRP Aquifer Pumping Effects Spreadsheet
  • Spreadsheet Explanation – Once you open the file, click Slide Show or press F5 to begin the presentation.
• Irrigation History in the Rathdrum Prairie and Spokane Valley – 2015
• Supporting Data: Spreadsheets and Shapefiles – 2011
• Water budgets for Coeur d’Alene Lake, Idaho, water years 2000–2005. – Maupin and Weakland – 2009
• Spokane Valley-Rathdrum Prairie Response Functions (IWRRI) – 2008
• Hydrogeologic Framework and Surface Water Leakage Studies in the Southern SVRP Aquifer – Grader, Nimmer, and Ralston – 2008
• Visualizing Groundwater and Surface Water Interactions in the Spokane Valley-Rathdrum Prairie – 2008
• Well Location Criteria – Ralston Hydrologic Services, Inc. – 2008
• Evaluation of Existing Gravity Observations in the Rathdrum Spokane Aquifer – Sprenke – 2006
• Gravity Acquisition and Depth to Basement Modeling of the Spokane Valley and Rathdrum Prairie Aquifer – Oldow and Sprenke – 2006
• Hydrologic Investigation and Groundwater-Flow Model of the Spokane Valley-Rathdrum Prairie Aquifer – 2005
• Rathdrum Spokane Aquifer Study – 2004

Spatial Information & Model Data

• Spatial Coverages – 2015
• SVRP MODFLOW Model Data Files – 2007
• Data Policies for the Spokane Valley-Rathdrum Prairie Project – 2005

Committee Meeting Documents

• Management Advisory Committee
• Modeling Committee
• Policy Advisory Committee
• Technical Advisory Committee

About the Committees

The Management Advisory Committee was composed of officials from the three cooperating agencies. Their role was to guide the study for the long-term, effective water management of the Spokane Valley-Rathdrum Prairie aquifer.

Involved stakeholders interested in lending support to the project participated on the Policy Advisory Committee. This committee was designed to deal with non-technical issues related to water management, water use, and policy decisions.

The Technical Advisory Committee was composed of technical subject-matter experts (hydrogeologists, hydrologists, and modelers) who had direct experience working in the Spokane Valley or Rathdrum Prairie aquifer or surface water drainages. This committee provided technical expertise when specific technical issues arose.

Related Links

• USGS Publications and Products
• Spokane River Temperature Profile
• Rathdrum Prairie CAMP
• Rathdrum Prairie GWMA
• USGS Lake Coeur d’Alene Water Budget Development