USB GW-SW Interactions-Phase 2

The IDWR hydrologist position for this project was vacant for nine months of the contract term, which limited the amount of work accomplished from the work that was proposed originally.

The following work was completed during the contract term, but does not have descriptive metrics to report for the database:

The aquifer characterization, water budget, dye tracer tests, and borehole dilution tests were not completed. Data compiled to use in the future for the aquifer characterization in the Lemhi included the following: 208 well drilling logs, stream flow data, seepage runs, and groundwater level measurements. This work does not have a descriptive metric in the database.

Samples for isotopic water analysis were collected at five locations four times (three wells, the adjacent Lemhi River, and the L-7 irrigation ditch).

Depth to water was measured in 21 wells located in the Lemhi from January 2014 to May 2015. Nine wells were continuously measured with sensors and 12 were manually measured on a biweekly schedule. May 2015, 17 more wells were added to the monitoring network; currently 21 wells are continuously measured and 17 manually measured.

One seepage run was completed on the 60 mile mainstem of the Lemhi River in 2014; measurements were made in August and October.

Originally E.c.1.15- Intensively monitored watershed work was incorrectly identified as part of this project. Intensively monitored watershed work was not completed through this project.

The following information was reported under metric E.1.c.9 Stream gauging data and was collected in 2014 and 2015. There were 17 gauges monitoring approximately 171.3 stream miles of the Lemhi River (worksite #1 – HUC #17060204) and 7 gauges monitoring approximately 476.7 stream miles in the upper Salmon and Pahsimeroi (collectively worksite #2 - HUC #17060201 and #17060202 respectively).

Worksite #1 metric E.2.b.1 modeling and data analysis Lemhi Mike Basin Model: The full Lemhi Mike Basin Model (MBM) was maintained by updating plumbing of the reaches, nodes, and catchments to better represent the basin. Also the MBM updated the water data to WY 2014 by including new rainfall-runoff data, diversion data, and streamflow data. The plumbing and water data update required the model to be re-calibrated using a calibration period from 2008 to 2014.

The Lemhi MBM was augmented with groundwater information which uses two different methods to estimate groundwater impacts in the basin. A linear reservoir built into the MBM was used to estimate quick (<10 day travel time) groundwater return flows and then an analytical solution using the method developed by CH2mHill (2014) that creates a response function to estimate the quantity of groundwater return to the system at a particular node and event.

The benefits of this phase of the project include gaining a more thorough understanding of the basin hydrology through an aquifer characterization and water budget development while maintaining our current monitoring network. This information will provide knowledge about how irrigation practices affect the overall movement, timing, and volume of water in both the surface and groundwater storage reservoirs. The greater understanding and conceptualization of the system and basin hydrology will guide the development of the best tools to represent the system through groundwater modeling efforts. A calibrated Mike Basin Model that represents the surface water component of the basin while gradually integrating the groundwater system provides a tool for collaborators to plan and landowners to see the benefit of habitat and streamflow restoration projects by the USBWP Technical Team.