Municipal Water Storage Level II, Phase I
Trihydro provided growth and demand projections, hydrologic modeling, alternatives assessment, and more to a project that aimed to evaluate options for enlarging the City of Cheyenne’s raw water storage system capacity to support future growth.
The Wyoming Water Development Commission (WWDC) contracted Trihydro to provide professional services for the Cheyenne Storage Project Level II Study on behalf of the Cheyenne Board of Public Utilities (BOPU). The project aimed to evaluate options for enlarging the City of Cheyenne’s raw water storage system capacity to support future growth.
BOPU uses a complex system that includes trans-basin diversions, water-right exchanges, reservoirs, pipelines, and other infrastructure to supply surface and groundwater to the City of Cheyenne. As the City’s population and water demands increase, additional water sources will be required. Additionally, the BOPU’s water supply faces several critical short- and long-term risks and vulnerabilities. The purpose of the Project was to increase the firm yield of BOPU’s System to meet near- and mid-term future demands of the BOPU’s customers in the form of system improvements and groundwater/surface water supply expansion, while mitigating the most serious vulnerabilities that threaten the System.
To support the project goal, Trihydro provided the following services:
- Growth and demand projection analysis
- Hydrologic modeling and infrastructure analysis
- Conceptual design for storage improvements
- Cost estimates
- Geotechnical investigations
- Environmental analysis
- Economic analysis
- Project management
Growth and Demand Projections
Trihydro and AVI Professional Corporation developed growth and demand projections for the BOPU service population. We used the demand projections to determine when potential shortages could occur. Based on a 50-year planning period, the demands in 2018 of 14,500 acre-feet per year were expected to increase up to 27,477 acre-feet per year in 2067.
Hydrologic Modeling
Project efforts also focused on developing a modeling and simulation hydrologic model of BOPU’s water supply system to simulate monthly operation and behavior of the system’s reservoirs, natural inflows, rivers, streams, pipelines, groundwater output, and treatment facilities. We calibrated the model to BOPU’s historical records and used it to evaluate the system’s current state, determine future shortage potential using the projected demand results, and identify potential improvements.
Evaluating Project Alternatives
Trihydro, in collaboration with BOPU and WWDC, used the model to identify, evaluate, and screen potential alternatives. Projects were screened to determine the top three alternatives that provide the most benefits with the least impact (e.g., economic, environmental, or otherwise). The top three options based on the characteristics, benefits, and impacts of the 52 identified alternatives include:
- Connecting New North Crow water to the potable treatment facility
- Crystal and Granite outlet rehabilitation and bypass pipeline
- Undertaking efficiency improvement for the Little Snake collection
Benefits of these alternatives include additional yield and supply, risk reduction, independence from the Colorado River Compact Curtailment, and proximity to Cheyenne.
Our team undertook conceptual design, cost estimation, geotechnical investigation, environmental analysis, and economic analysis for each alternative. With assistance from RJH Consultants, Inc., the condition of the outlet works at the dams of Crystal and Granite Reservoirs was also evaluated. Based on the project results, continued development of each selected alternative is warranted, and the BOPU is performing additional evaluation.
