Upper Green River Basin Instream Flow Analysis – Wyoming Water Development Office

Follum Hydrologic Solutions (FHS) is conducting a Level I instream flow study for six stream segments in the Upper Green River Basin in Wyoming on behalf of the Wyoming Water Development Office. The project evaluates historic, current, and unappropriated streamflows to support defensible instream flow recommendations that balance ecological needs with existing water uses. FHS integrates long-term gage records, reconstructed streamflow datasets, water rights inventories, and geospatial analysis to quantify natural (“virgin”) flows, diversions, consumptive use, return flows, and storage influences across each study reach.

The project applies modern hydrologic science and GIS-based workflows to deliver actionable results. FHS reconstructs streamflow records using bias-corrected continental-scale hydrologic model outputs, analyzes monthly and daily flow exceedance statistics, and evaluates the feasibility of upstream storage to address seasonal instream flow deficits. The study produces detailed maps, datasets, and reports that clearly document methods, assumptions, and findings, providing WWDO with a transparent and scientifically robust foundation for instream flow decision-making and future basin-wide studies.