Lolo Creek, Missoula County

Background

Lolo Creek, a perennial tributary to the Bitterroot River, has in some years become intermittent in the lower reaches during late summer and early fall. The creek, designated as a critical bull trout habitat, is a perennial fishery and water resource from above Lolo Hot Springs to its confluence with the Bitterroot River. Montana Fish, Wildlife and Parks list bull trout as threatened and a species of concern. They spawn from August through November, times that the lower reaches of the Creek are dry in some years. The Lolo Creek alluvial aquifer is an important water resource for domestic and municipal wells and is likely in direct communication with the surface water. Population growth and the addition of more water wells has resulted in higher volumes of groundwater withdrawals.

Purpose

The purpose of this GWIP project is to determine the cause(s) of changes in streamflow character in the lowest reaches of Lolo Creek that have resulted in the channel occasionally being dry. The GWIP investigation will: 1) evaluate the surface-water budget components to determine correlations with streamflow gains and losses; and 2) investigate how groundwater stresses influence Lolo Creek streamflow.

Project Scope

Water levels in a network of 75 wells, and stage and flows at 13 surface-water sites, were measured from Spring 2015 through December 2017. Twenty-six dedicated monitoring wells were installed to monitor groundwater/surface-water interactions. Aquifer tests were conducted to estimate the aquifer properties. The hydrogeologic framework, groundwater budget, and groundwater flow model were developed to help evaluate the hydrologic system and the cause-and-effect of different stresse.

Project Status

Data interpretation and model development are completed. Report is under final review.

Project Reports

• Aquifer test completed in the northern Bitterroot Valley, Lolo, Montana (Myse, T., 2022)
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Project Personnel

Ali Gebril	Associate Research Hydrogeologist, Groundwater Modeler
Cam Carstarphen	Associate Research Hydrogeologist

Presentations

• Modeling surface and groundwater interaction to study dewatering of the end reaches of Lolo Creek, Montana. Presentation to the Montana American Water Resources Association (AWRA), October 14, 2022, Butte, Montana.
• Lolo Creek Project, Ground Water Investigation Program, Montana AWRA, October 2017 (Carstarphen and Wheaton, 2017)
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• GWIP Lolo Creek Project Handout (Carstarphen and Wheaton, May 2017)
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• GWIP Lolo Creek, 2016 Lolo Creek Watershed Symposium, September 14, 2016 (Carstarphen and Wheaton)
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Link to Project Data

Data collected for this project can be accessed through the Ground Water Information Center (GWIC) database:

Download project data from GWIC

Content last updated: 5/11/2022 1:16:42 PM