Reservoir Feasibility Study

Big Horn Basin
Wyoming

Services Provided

Market

Regulatory Agency Involved
Wyoming Water Development Commission

WWDC_Feasibility_StudyII_Nowood_2
The Wyoming Water Development Commission contracted with Trihydro in 2010 to perform a feasibility study and conceptual engineering analysis of potential reservoir storage opportunities within the Nowood River Watershed (Watershed). The goal of the Level II Study is to explore opportunities to develop reservoir storage within the Watershed, which will benefit Wyoming and its residents by addressing late-season water supply shortages evidenced within the Watershed. Successful execution of the Level II Study will provide the technical basis for establishing the Purpose and Need for developing reservoir storage.

Trihydro, in association with our team partners, modeled surface water shortage and availability for storage, identified potential storage sites, and evaluated potential storage site characteristics to determine the most viable storage sites in the Watershed.  

Work completed as part of the Project includes development of a StateMOD watershed hydrologic model to simulate physical and available flows as well as shortages in the Watershed. The model also identified available flows (meaning flows that are not currently put to beneficial use under existing water rights) for development or storage throughout the Watershed. Work completed as part of the Project also expanded the evaluation of potential reservoir sites suited for storing available flows in the Watershed so that the flows could be released to meet late season shortages.

The Level I Study identified 35 potential storage sites. Five additional sites were identified during the Level II work.  Sites were evaluated to determine which might provide the most benefit to the Watershed with the least impact (economic, environmental, or otherwise). More detailed investigations, including site visits to evaluate geotechnical and geological conditions, evaluation of environmental considerations, archeological investigations, discussions with landowners and agencies, and development of conceptual level designs and cost estimates were completed for a short list of sites that appeared to provide the most overall value to the Watershed.

Based on evaluation of the characteristics, benefits, and impacts of the 40 identified potential storage sites, two sites were recommended for further evaluation: an expansion to Meadowlark Lake and construction of a new reservoir on Alkali Creek.  Meadowlark Lake is located on the Bighorn National Forest near the headwaters of Tensleep Creek. Alkali Creek is a small tributary to Paint Rock Creek, which is a primary tributary to the lower Nowood River.  Although both of these alternatives appear to meet a portion of the needs documented in the Watershed and identified by the hydrologic model, alternative sites will continue to be evaluated to establish purpose and need for water storage facilities best suited for benefiting residents in the Watershed and the State of Wyoming.  
     
Additional investigations and evaluations for these sites are underway and will include continued data collection and refinement of the StateMOD model, geotechnical investigations, conceptual designs, and cost estimates. Continued coordination with local landowners and interested and affected agencies to assess potential benefits and impacts, as well as to better define permitting and NEPA requirements. Further economic analysis, including local stakeholder’s willingness to pay for storage water will also be evaluated.  
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A list of 40 potential storage sites was developed and evaluated to determine the most beneficial site(s) for reducing late-season water supply shortages.