Reservoir Environmental Impact Study

Trihydro provided water allocation modeling for the West Fork Reservoir Project, which aims to offer additional irrigation water during the late season to land spanning Wyoming and Colorado in the Little Snake River Basin.

The West Fork Reservoir Project involves constructing a new dam and reservoir along West Fork Battle Creek in the Little Snake River Basin of Carbon County, Wyoming. In addition to increased irrigation water, the project will have secondary environmental advantages to the watershed. Coordinating the management of this new reservoir alongside the existing High Savery Reservoir is expected to yield basin-wide benefits.

The project must comply with the National Environmental Policy Act (NEPA), which requires an environmental impact statement (EIS) to disclose potential environmental impacts associated with the project and consider project alternatives.

Water Allocation Modeling

Trihydro is assisting our partner, SWCA Environmental Consultants, the West Fork EIS project lead, with water allocation modeling of the proposed action and alternatives to determine water availability and impacts under multiple possible future hydrologic scenarios. This involved creating model input pre-processing tools to facilitate probabilistic modeling.

We are performing these modeling analyses using the Colorado Decision Support System (CDSS) tools, which include the consumptive use model, StateCU, and the allocation/water rights administration model, StateMod. Trihydro also performed model review and validation, which included comparing remote sensing-based crop evapotranspiration estimates with StateCU-produced values.

Leading a Stream Stability Study

In addition to the water quantity simulations, Trihydro reviewed existing water quality models and led a stream stability study. To support this study, Trihydro crews prepared for the West Fork Battle Creek and Battle Creek data collection using desktop review to define stream reaches. Following this, the crews collected the required data and implemented the newest version of the Wyoming Stream Quantification Tool version 2.0 to assess stream stability.

In the field, crews performed reach walks to determine representative sub-reaches and collected data including cross sections, pebble count, Large Woody Debris Index, water velocity and depth, Bank Erosion Hazard Index/Near Bank Stress, and bankfull indicators, along with ample photo documentation. We documented the stream quantification tool results in a technical memorandum.

Results of these analyses are being documented in sections of the draft EIS, which will be finalized following agency and public review.