Hydrologic Investigation of the Smith River Watershed, Meagher County, Montana with an emphasis on Ground-Water/Surface-Water Interaction

Problem:

The Smith River watershed is an important recreational and agricultural area in Meagher and Cascade counties in west-central Montana. Thousands of visitors travel to the area annually to float and fish the Smith River and most of the water used to irrigate 36,000 acres of the upper Smith River watershed is withdrawn from the Smith River or its tributaries. During the recent drought, streamflow has not been sufficient to meet the needs of all irrigators and recreationists, and minimum streamflow for fish viability has not been met on several occasions. Largely in response to the lack of available surface water for irrigation, some irrigators have switched or proposed switching from flood to sprinkler irrigation and some have considered using ground water as a source of irrigation water. The effect of these changes in irrigation practices on the hydrologic system in the upper Smith River watershed is not well understood. Existing data are not sufficient to adequately describe the hydrologic system and the existing interaction between the surface-water and ground-water systems in the watershed.

Objective:

The objectives of this proposed study are to 1) assess the ground-water system within the Smith River watershed, including characterization of the hydrogeology and development of a conceptual ground-water-flow model, and 2) assess the interaction between ground water and surface water along the Smith River and its major tributaries. The study area will include the Smith River watershed upstream of Hound Creek. Study activities will focus on collection and analysis of data on the Smith River and its major tributaries and ground water within the Quaternary and Tertiary sedimentary aquifers. Although this study will improve the understanding of the basic hydrology and ground-water/surface-water interaction within the watershed, it will not address the impacts of individual water users. This study is designed to provide large-scale background information that will improve the knowledge and understanding of the hydrology of the area and provide a basis for potential future studies of a more-detailed nature.

Approach:

The objectives of this study will be accomplished by completing the 13 tasks listed below. These tasks are listed in the general order in which they will be completed; however, the timing of several of these tasks will overlap.

Existing data compilation and review

Install and operate streamflow gaging stations on the Smith River near Eden and near Fort Logan, and continue to operate the Smith River gaging station below Newlan Creek

Initial reconnaissance of Smith River

Inventory and surveying of existing wells

Synoptic streamflow measurements

Synoptic ground-water level measurements

Installation of shallow wells, minipiezometers, and temperature loggers

Monitoring of wells, minipiezometers, and stream stage

Temperature monitoring

Generation of water-table and gain/loss maps

Water-chemistry sample collection and analysis

Estimation of aquifer properties and streamflow gains and losses

Report writing, review, and publication

Status:

The initial phases of the study are currently in progress. The new streamflow gaging stations near Eden and near Fort Logan were installed and are now operating as real-time stations. There are currently 4 streamflow gaging stations in operation on the Smith River with data available online at http://waterdata.usgs.gov/mt/nwis/current?type=flow.

Publications: none yet

Cooperator: Meagher County Conservation District

Project Chief: Rod Caldwell