Upper Salmon Basin Groundwater – Surface Water Interactions, P4

The overarching objective of the Upper Salmon Basin Groundwater-Surface Water (USB GW-SW) Interactions project is to better define groundwater-surface water interactions in the Lemhi Basin in support of ongoing salmonid recovery efforts. This is a multi-phase project, which began in 2011. Specific objectives include: 1) an assessment of the contributions to streamflow from natural runoff, irrigation return flows, and aquifer discharge, and 2) a determination of how irrigation practices affect the location, timing, and volume of streamflow. These objectives are being accomplished through the collection of surface water, groundwater, and diversion rate data that are then entered into the Lemhi River Basin Model (LRBM), which can be used to predict and compare the hydrologic impacts of potential water use scenarios.

Tasks completed during Phase 4 include streamflow data collection, groundwater data collection, soil moisture data collection, compilation and publishing of historical streamflow data, assessment and modification of data collection methods, analysis of changes to irrigation practices, upgrading and updating the LRBM and development of interactive tools that enable model users to explore and visualize model output data. Data was collected at two worksites, the Lemhi Basin and the Upper Salmon Basin. An IDWR report was completed and streamflow data has been posted to the IDWR streamflow data repository available at https://research.idwr.idaho.gov/apps/hydrologic/aquainfo/Home/Data#!/. The data and analyses from Phase 4 will be used to conduct more robust analyses under Phase 5 to address the specific objectives stated above, as well as improve the understanding of Lemhi Basin hydrogeology and salmonid habitat suitability. Phase 4 continued work from PCSRF contracts 010 10 SA, 002 13 SA, and 004 15 SA.

The project generally adhered to the proposal; however, there were a few variations due to shifting stakeholder priorities, and logistical complications presented by the COVID-19 pandemic. The largest variation from the original proposal was an amendment to extend and increase the scope of work of the project to include LRBM conversion/recalibration and public tool development. Additional modifications included the following: Task 3: Aerial Photography Analysis of Changes in Irrigation Practices- The current irrigation practices, as well as those occurring in 2015 have been summarized; however, a more robust historical analysis of aerial photography has yet to be completed. Staff changes within IDWR have necessitated the hiring of a contractor to assist with this work, which is now slated to be completed during the next project phase; Task 4: Conversion of the LRBM from MIKE Basin to MIKE Hydro Basin- This task was 50% complete as of the end of this project phase, as a result of unforeseen modelling demands outside of the conversion (e.g., Lemhi Water Rights Settlement Negotiations); and Task 5: MIKE Basin Integration Tool- the scope of this tool was expanded to include a large suite of interactive tools that allow model users to explore and visualize both input and output model data.

This work supports the overarching objective to protect and improve salmonid recovery for Chinook salmon and steelhead in the Lemhi River basin by addressing the limiting factor of diminished streamflow during critical periods of the year. This project is an ongoing effort to: 1) assess the contributions to streamflow of natural runoff, irrigation return flows, and aquifer discharge, and 2) determine how irrigation practices affect the location, timing, and volume of streamflow. This project supplies data and information which are important for predicting the effectiveness of salmonid recovery efforts.