A look below the surface in the Lolo Creek watershed

Working with the Montana bureau of mines and geology

In 2015, lower Lolo Creek was chosen as a Montana Bureau of Mines and Geology (MBMG) Ground Water Investigation Program (GWIP) project site. Between Spring 2015 and December 2017, the MBMG monitored ground and surface water throughout the Lolo Creek drainage to “evaluate the surface-water budget components to determine correlations with streamflow gains and losses”; and “investigate how groundwater stresses influence Lolo Creek streamflow” (GWIP Overview).

Why Lolo Creek?

Over the last ten years, there has been five dry channel events in Lolo Creek – instances in which Lolo Creek has either completely or almost ran dry. Designated a critical bull trout habitat, these events compromise the habitat of an already threatened species- and give warning about the potentially jeopardized water supply in the alluvial aquifer. The GWIP “conducts research on specific hydrogeologic issues in areas that are ranked as the most urgent within the State” and found that the factors above gave Lolo Creek high priority (GWIP Overview).

To conduct this research, staff at the MBMG monitored the ground and surface water through the following methods:

Surface water

Staff gauges instrumented with continuous dataloggers along Lolo Creek and on the main ditch diversions (blue squares, fig. 2). This network is operated in conjunction with DNRC. Monthly manual discharge measurements document flow conditions and patterns and indicate points of net loss and gain.

Groundwater use and flow

Currently, 48 wells and piezometers are measured monthly across the watershed. Thirteen of these have been instrumented with dataloggers recording hourly water levels. Measured groundwater-level fluctuations (daily and seasonal), precipitation, and estimated use and evapotranspiration will be used to calculate and model a groundwater budget.

Groundwater/ surface water interaction

Groundwater elevations matched with surface water elevations will confirm losing and gaining reaches; ground- water monitoring sites include wells across the study area plus shallow wells installed at four staff gauge sites. These piezometers are instrumented with temperature sensors. Isotopes have been collected at all stream sites and will be correlated with groundwater isotopes during synoptic sampling events.

Precipitation Data

Meteorological data are collected at two sites. These stations, installed by the Montana Climate Office, will provide inputs to water budget calculations.” (Carstarphen and Wheaton, 2017)

After data collection, the team at MBMG has been working to create products for more informed science- based water management, including comprehensive data sets, a groundwater budget for Lolo Creek alluvial aquifer, various groundwater models, and interpretive reports. We are looking forward to learning more about how water moves through the Lolo Creek Watershed!

For more information about the Groundwater Investigation Program and the Lolo Creek Project, you can find the Montana Bureau of Mines and Geology GWIP webpage through the link below.