Clear Lake Aquifer, Sheridan County

Background

The Clear Lake aquifer is a significant water resource in eastern Montana that occupies a broad buried valley formed by the ancestral Missouri River. The Clear Lake aquifer contains sand and gravel deposited by the ancestral Missouri River and by later glacial meltwater streams. These deposits form a complex aquifer system with some areas capable of supporting high-yield irrigation wells. The U.S. Fish and Wildlife Service (USFWS) Medicine Lake Wildlife Refuge manages many of the lakes and wetlands overlying the aquifer. Irrigation effects to these wetlands have been a concern of the Refuge. The Sheridan County Conservation District (SCCD) currently manages irrigation development of the aquifer. Results of this report will be used by a technical advisory committee that reviews water-rights applications.

Purpose

The purpose of the project is to assist the SCCD in managing and allocating groundwater from the Clear Lake aquifer by: 1) determining how much water can be developed from the aquifer without significantly affecting surface-water and groundwater resources, and 2) evaluating if water development and other land uses have affected water quality in the aquifer.

Project Scope

Fieldwork included water-level and water-quality monitoring, water-use monitoring, and test drilling. A potentiometric map for the aquifer, aquifer properties, analysis of hydrographs, and examination of water quality characterized the aquifer. A conceptual model and a numerical groundwater flow model were developed for the South Medicine Lake focus area. Geologic cross sections were developed to define the hydrogeologic framework for the model. The transient groundwater flow model was used to simulate increased water use in the focus area.

Results

Predictive model simulations evaluated changes in the groundwater and surface-water flow systems from increased pumping. A simulation with twice the number of irrigation wells and pumping rates similar to 2015 indicated no change in water levels near Big Muddy Creek, whereas a simulation with twice the number of irrigation wells that pump >2 times the 2015 rate indicated groundwater-level declines near Big Muddy Creek. Water quality in the upper outwash gravel zone is generally acceptable for irrigation, while much of the alluvial gravel zone is not.

Project Reports

• Hydrogeology and water management of the Clear Lake aquifer, with emphasis on the South Medicine Lake management area (Reiten, J., and Chandler, K., 2021)
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Download plate 2 (9.8 MB)
Download plate 3 (4.9 MB)


• South Medicine Lake area of the Clear Lake aquifer: Groundwater Model report (Chandler, K., and Reiten, J., 2019)
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Download report (69 MB)


• Clear Lake Aquifer focused groundwater modeling report, Medicine Lake area, Sheridan County, Montana (Chandler, K. and Reiten, J. and in review).

Presentations

• Clear Lake Aquifer GWIP Project. Presentation at the Medicine Lake Wildlife Refuge, July 12, 2017.
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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: 5/10/2022 11:41:55 AM