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Green River Basin Instream Flows 2025 Study

Pursuant to Wyoming State Statute §41-3-1004(a) the Wyoming Water Development Commission is commencing the “Upper Green River Basin Instream Flows 2025 Study” to determine the feasibility of providing instream flows from unappropriated direct flows or from new storage facilities in 6 stream segments in the Upper Green River Basin. Follum Hydrologic Solutions (FHS) has been contracted to complete the Level I instream flow study. The stream segments to be studied in this area are:

  • North Horse Creek, tributary of Horse Creek, tributary of the Green River.

oStream length of 16.44 miles

  • Maki Creek, tributary of North Cottonwood Creek, tributary Cottonwood Creek, tributary of the Green River.

oStream length of 3.55 miles

  • South Beaver Creek, tributary of Beaver Creek, tributary of the Green River.

oStream length of 5.98 miles

  • South Horse Creek, tributary of Horse Creek, tributary of the Green River.

oStream length of 12.77 miles

  • Rock Creek, tributary of the Green River.

oStream length of 6.39 miles

  • Klondike Creek, tributary of the Green River.

oStream length of 2.75 miles

 

The project evaluates historic, current, and unappropriated stream flows using long-term stream gage records, reconstructed flow datasets, water rights inventories, and geospatial analysis. These tools are used to quantify natural (“virgin”) flows, diversions, consumptive use, return flows, and the influence of storage within each study reach. The goal is to provide scientifically defensible information that can be used to determine whether instream flow recommendations are feasible.

FHS applies modern hydrologic science and GIS-based workflows to deliver transparent and actionable results, including the following:

  • streamflow records supplemented by reconstruction methods using bias-corrected outputs from continental-scale hydrologic models
  • monthly and daily flow exceedance statistics
  • feasibility of upstream storage to address seasonal instream flow deficits.

Project deliverables include detailed maps, datasets, and technical reports that clearly document methods, assumptions, and findings, providing a strong foundation for instream flow decision-making and future basin-wide studies.

If you would like to learn more about the instream flow program and previous studies those can be found at: https://wwdc.state.wy.us/instream_flows/instream_flows